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Contributors:A. Velazquez Blazquez (Royal Meteorological Institute of Belgium (RMIB)), N. Clerbaux (Royal Meteorological Institute of Belgium (RMIB)), EA. Baudrez Velazquez Blazquez (Royal Meteorological Institute of Belgium (RMIB)), S. Dewitte (Royal Meteorological Institute of Belgium (RMIB)), S. Nevens (Royal Meteorological Institute of Belgium (RMIB))
Issued by: RMIB/Clerbaux
Date: 0428/1211/20202023
Ref: C3SC3S2_D312bD312a_Lot1.2.12.5.1-v2v1.0_202003202303_ATBD_ECVEarthRadiationBudget_v1.1
Official reference number service contract: 2018/ C3S_312bD312b_Lot1_DWD/SC1.1.5.1-v2.0_202003_ATBD_ECVEarthRadiationBudget_v1.1
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History of modifications
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1Note: In the contract, this deliverable was originally ATBD - Earth Radiation Budget CERES TCDR v2.0 + ICDR v2.x (OLR, RSF) |
List of datasets covered by this document
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List of datasets covered by this document
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2Note: In the contract, this deliverable was originally Dataset - Earth Radiation Budget CERES TCDR v2.0 (OLR, RSF)
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Acronyms
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Acronym
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Definition
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ACRIM
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Active Cavity Radiometer Irradiance Monitor
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ATBD
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Algorithm Theoretical Basis Document
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ATLAS
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Atmospheric Laboratory for Applications and Science
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C3S
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Copernicus Climate Change Service
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CDR
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Climate Data Record
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CDS
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Climate Data Store
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CF
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Climate and Forecast
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DIARAD
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Differential Absolute RADiometer
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ECMWF
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European Centre for Mediumrange Weather Forecasts
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ECV
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Essential Climate Variable
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ERB
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Earth Radiation Budget
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ERBE
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Earth Radiation Budget Experiment
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ERBS
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Earth Radiation Budget Satellite
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EURECA
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European Retrievable Carrier
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FY
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Feng Yung
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GCOS
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Global Climate Observing System
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ICDR
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Interim Climate Data Record
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ISP
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Solar Constant Gauge
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ISS
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International Space Station
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LASP/TRF
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Laboratory for Atmospheric and Space Physics / Total Solar irradiance (TSI) Radiometer Facility
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NASA
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National Aeronautics and Space Administration
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NIST
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National Institute of Standards and Technology
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NOAA
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National Oceanic and Atmospheric Administration
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NPL
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National Physical Laboratory
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PMO
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Physikalisches und Meteorologisches Observatorium
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PREMOS
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Precision Monitor Sensor
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RMIB
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Royal Meteorological Institute of Belgium
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SATIRE
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Spectral And Total Irradiance REconstructions
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SIM
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Solar Irradiance Monitor
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SMM
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Solar Maximum Mission
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SOHO
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Solar and Heliospheric Observatory
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SOLCON
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Solar Constant
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SORCE
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Solar Radiation and Climate Experiment
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SOVA
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Solar Variability
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SOVIM
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Solar Variability Irradiance Monitor
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TCDR
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Thematic Climate Data Record
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TCFM
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Temperature Control Flux Monitor
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TCTE
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Total solar irradiance Calibration Transfer Experiment
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TIM
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Total Irradiance Monitor
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TOA
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Top Of Atmosphere
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TSI
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Total Solar irradiance
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TSIS
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Total and Spectral Solar Irradiance Sensor
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UARS
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Upper Atmosphere Research Satellite
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VIRGO
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Variability of solar IRradiance and Gravity Oscillations
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WRC
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World Radiation Center
Scope of the document
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Executive summary
The Total Solar Irradiance (TSI) quantifies the amount of solar energy that is received by the Earth.
TSI is defined as the amount of solar power that reaches the Earth’s top of the atmosphere per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance.
The TSI is a fundamental variable governing the climate system, and is recognized as ECV by the Global Climate Observing System (GCOS). Within the Copernicus Climate Change Service (C3S), a long composite Climate Data Record (CDR) is constructed from measurements of the TSI measured by an ensemble of space instruments. The measurements of the individual instruments are first put on a common absolute scale, and their quality is assessed by intercomparison. Then, the composite time series is the average of all available measurements, on a daily basis.
This ATBD fully describes and justifies the successive steps implemented in the data processing and most of the information here contained has been reproduced from the two reference papers [D1] and [D2].
1. Introduction
The first Total Solar Irradiance (TSI) measurement from space was made with the Temperature Control Flux Monitor (TCFM) on Mariner 6 and 7 by Plamondon (1969). Continuous measurement of the TSI started with the Earth Radiation Budget (ERB) instrument on Nimbus 7 by Hickey et al. (1980). Continuous monitoring with an ageing corrected TSI instrument started with the Active Cavity Radiometer Irradiance Monitor (ACRIM) 1 instrument on the Solar Maximum Mission (SMM) by Willson et al. (1980). A summary of TSI space instruments is given in Table 1.
The instruments used for the TSI measurement are electrical substitution cavity radiometers. Their core detector consists of a blackened cavity in which nearly all incident radiation flowing through a precision aperture is absorbed. The thermal effect of the absorbed optical power is measured by comparison with the thermal effect of known electrical power.
A TSI radiometer ages by exposure to solar UV radiation. For ageing correction, a backup channel is used, for which the total solar UV exposure is kept low such that the ageing of the backup channel is negligible.
Relative variations of the TSI in phase with the 11-year solar cycle of the order of 1 W/m² are now well established, as summarized by Dewitte & Nevens (2016) [D1]. Apart from these true TSI variations, differences in the absolute level above 1 W/m² are measured by different instruments indicating limitations of the absolute accuracy.
As the Sun is nearly a point source, TSI radiometers use a view-limiting mechanism to eliminate the entrance of all except direct solar radiation into the cavity. Classical radiometers place a large view-limiting aperture in front of a small precision aperture. In this geometry, scattering and diffraction around the edges of the view-limiting aperture increase the amount of solar power flowing through the precision aperture. When this effect is underestimated it may lead to a too-high measurement of the TSI.
The Total Irradiance Monitoring (TIM) radiometers use an alternative geometry where the small precision aperture is put in front of the larger view-limiting aperture. In this geometry, scattering and diffraction around the edges of the precision aperture decrease the amount of solar power flowing through the view limiting aperture. When this effect is underestimated it may lead to a too-low measurement of the TSI.
Table 2 summarizes the equivalent TSI at a solar minimum measured by three independent instruments: TIM on the Solar Radiation and Climate Experiment (SORCE) in 2003, the Differential Absolute Radiometer (DIARAD) as part of the Solar Variability Irradiance Monitor (SOVIM) in 2008 and TIM on the Total Solar Irradiance Transfer Experiment (TCTE) in 2013. We consider TIM/TCTE as more reliable than TIM/SORCE, since TIM/TCTE went through additional pre-flight characterizations as compared to TIM/SORCE. A TSI level at a solar minimum of 1362 +/- 0.9 W/m² can be derived from the combination of DIARAD/SOVIM and TIM/TCTE [D2].
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Instrument 3
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Platform(s)
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Used
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Operation period(s)
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References
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TCFM
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Mariner-6 & 7
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No
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1969
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Plamondon (1969)
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ERB
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Nimbus 6
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No
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1975
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Hickey et al (1976)
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Nimbus 7
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Yes
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1978
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Hickey et al (1980)
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ACRIM 1
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SMM
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Yes
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1980-1989
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Willson et al. (1980)
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Solcon 1
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Spacelab 1
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No
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1983
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Crommelynck et al (1987)
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ERBE
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ERBS
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Yes
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1984-2003
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ERBE(1986)
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NOAA-9
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Yes
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1985-1989
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ERBE(1986)
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ACRIM 2
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UARS
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Yes
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1991-2001
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Willson(1994)
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Solcon 2
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Atlas 1
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No
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1992
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Crommelynck et al (1994)
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Sova 1
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Eureca
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Yes
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1992-1993
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Crommelynck et al (1994)
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Sova 2
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Eureca
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Yes
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1992-1993
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Romero et al. (1994)
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ISP-2
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Meteor-3 7
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No
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1994
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Sklyarov et al. (1996)
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DIARAD/VIRGO
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SOHO
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Yes
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1996-present
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Dewitte et al. (2004)
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PMO06V-A/VIRGO
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SOHO
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Yes
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1996-present
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Froehlich et al. (1997)
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ACRIM 3
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ACRIMSAT
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Yes
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2000-2014
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Willson et al. (2003)
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TIM
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SORCE
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Yes
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2003-present
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Kopp et al. (2005)
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DIARAD/SOVIM
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ISS
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Yes
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2008
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Mekaoui et al. (2010)
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SIM
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FY 3A
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No
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2008-2015
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Fang et al. (2014)
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SOVA
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Picard
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Yes
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2010-2014
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Dewitte et al. (2013a)
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Premos
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Picard
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Yes
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2010-2014
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Schmutz et al. (2012)
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SIM
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FY 3B
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No
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2011-present
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Fang et al. (2014)
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TIM
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TCTE
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Yes
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2013-present
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Kopp et al. (2016)
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SIM
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FY 3C
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No
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2013-present
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Wang et al. (2017)
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TIM
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TSIS-1
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Yes
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2018- present
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Kopp, G. (2020),
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Acronyms
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List of tables
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Table 1: Total Solar Irradiance space instruments (acronyms definitions in footnote). The instruments used in the C3S v3.0 and v3.1 daily TSI composite are highlighted in bold. Table 2 : Scaling factors and precision estimates (see Section 3.2) for the 12 input TSI timeseries. Table 3: Instrument precision estimated as root mean square (RMS) difference with SATIRE-S. Table 4: General characteristics of the C3S daily TSI composite CDR. Table 5: Total Solar Irradiance parameter. |
List of figures
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Figure 1: SATIRE-S daily TSI values (grey) and 121-days running mean (horizontal line at 1360.75 W/m² to illustrate the change in solar minima). Figure 2: NRLTSI2 daily values (grey) and 121-days running mean (horizontal line at 1360.45 W/m² to illustrate the stability of the solar minima). Only data onward of 1976 are shown. Figure 3: Timeseries of SATIRE-S (red) and NRLTSI2 (black) TSI reconstruction models after 121-days running mean. The daily NRLTSI2 values are shown in grey. Horizontal line at 1360.75 W/m² illustrates the change in solar minima. Figure 4: (rescaled) ERB timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 5: (rescaled) ACRIM1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 6: ERBS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 7: (rescaled) ACRIM2 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 8: (rescaled) DIARAD timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 9: PMO06 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 10: (rescaled) ACRIM3 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Some outliers are in red. Figure 11: (rescaled) TIM/SORCE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 12: (rescaled) SOVA/Picard timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 13: (rescaled) PREMOS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 14: (rescaled) TIM/TCTE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 15: (rescaled) TIM/TSIS-1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 16: Timeseries of individual TSI measurements after selection and harmonization. A 121-day running mean is used to remove the short-term solar noise. The 1361 W/m² horizontal line is shown to illustrate the stability between the solar minima. Figure 17: Illustration of the gap filling process. The black curve is an original TSI record with many data gaps (in this example the TIM/TCTE in 2014). The green curve is the SATIRE-S model. The red curve shows how the gaps can be filled by mixing the incomplete record with the (complete) SATIRE-S record. Figure 18: C3S composite daily TSI values (grey) and 121-day running mean (red). The NRLTSI2 model, with an offset of 0.31 W/m² to match the curves, is shown in black. |
General definitions
| Term | Definition | ||||
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Earth Radiation Budget (ERB) | The difference between the incoming radiant energy to the Earth (directly dependent on the TSI) and the outgoing radiant energy due to reflection and thermal emission. | ||||
Electrical substitution cavity radiometer | Radiant energy measurement principle in which the radiant energy absorbed in a cavity is equilibrated with electrical power dissipated in a second non-illuminated equivalent cavity. | ||||
Magnetogram | Image of the Sun showing the strength and the polarity of its magnetic fields. The image is taken by an instrument called magnetograph. | ||||
Scattering and diffraction | Change of light direction due to interaction with matter. The diffraction is a spreading of light without changing in the average direction, while scattering is the deflection of the light with a clear change of direction. | ||||
Astronomical Unit (A.U.) | Unit of length equal to the mean distance between the center of the Earth and the center of the Sun. | ||||
Irradiance | Flux of radiant energy per unit area. The irradiance is usually expressed in W/m² unit. | ||||
Solar cycles | The solar cycles are nearly periodic 11-year changes in the Sun's activity. | ||||
Solar minima, quiet Sun | The 11-year solar cycle is characterized by periods of least solar activity called solar minima or quiet Sun. During these periods the average TSI is also minimum. | ||||
Bright facula | A solar facula is a bright spot in the photosphere. This part of the Sun disk has higher TSI than its surrounding area. | ||||
Dark sunspot | Opposite to a facula, a sunspot is a part of the Sun disk that appears darker, i.e. with a lower TSI, than its surrounding area. The sunspots can be decomposed in two main regions: the central umbra (with the lowest TSI) and the surrounding penumbra (with higher TSI than in the central umbra). The sunspots are often organized in network. | ||||
Bias
| The bias (b) is the average value of the difference of the data (xi ) with respect to a reference dataset (ri ), where N is the number of data points:
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Climate Data Store (CDS) | The front-end and delivery mechanism for data made available through C3S. | ||||
Climate Data Record (CDR) | Sufficiently long, accurate and stable time series of a climate variable to be useful to address climate variability and change. | ||||
Interim Climate Data Record (ICDR) | An interim CDR is an extension of a CDR that meets some timeliness requirements needed in some applications, e.g. for use in the "State of the Climate" reports. These preliminary data might not be fully validated and may need to be reprocessed before inclusion in the finale CDR. |
Scope of the document
This document is the Algorithm Theoretical Basis Document (ATBD) for the generation of the version 3 of the Climate Data record (CDR) and Interim Climate Data Record (ICDR) v3.1 of daily Total Solar Irradiance (TSI) for the Copernicus Climate Change Service (C3S).
The aim of this ATBD is to provide a full description of the algorithms used to generate the CDR of daily TSI products, including the scientific justification for the algorithms selected to derive the product, an outline of the proposed approach and a listing of the assumptions and limitations of the algorithm.
Executive summary
The Total Solar Irradiance (TSI) quantifies the amount of solar energy that is received by the Earth. It is defined as the amount of solar power that reaches the Earth’s top of the atmosphere per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance. It is the most fundamental variable governing the climate system on Earth, and is recognized as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). Within the Copernicus Climate Change Service (C3S), a long composite Climate Data Record (CDR) is constructed from timeseries of daily TSI measured by an ensemble of space instruments. Currently 12 instruments are used in the composite.
The method can be summarized as follows:
• First, the 12 individual timeseries are quality checked by comparison with 2 models of the daily TSI (namely SATIRE-S and NRLTSI2 models).
• Second, the measurements of the individual instruments are put on a common absolute scale using optimized radiometric correction factors.
• Lastly, the composite is created as an average of the available measurements, on a daily basis.
The method is an adaptation of (Dewitte and Nevens, 2016) [ D1 ]. This ATBD fully describes and justifies the successive steps implemented in the data processing.
The document is presented as follows. Section 1 introduces the measurement principles and the main satellite missions that have been collecting TSI observations. Section 2 contains a detailed description of each of the 12 instruments’ records used to create the composite product. This section also presents important ancillary data such as the models and composites used for evaluation. Section 3 fully describes the algorithm used to create the composite. Finally, Section 4 briefly describes the output format for the TSI composite.
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The first Total Solar Irradiance (TSI) measurements from space were made with the Temperature Control Flux Monitor (TCFM) instrument on Mariner 6 and 7 (Plamondon, 1969). Continuous measurement of the TSI started with the Earth Radiation Budget (ERB) instrument on Nimbus 7 (Hickey et al., 1980). Continuous monitoring with an ageing corrected TSI instrument started with the Active Cavity Radiometer Irradiance Monitor (ACRIM1) instrument on the Solar Maximum Mission (SMM) (Willson et al., 1980). Since these early missions, TSI measurements have been continued with several space instruments listed in Table 1.
The instruments used for the TSI measurement are electrical substitution cavity radiometers. Their core detector consists of a blackened cavity in which nearly all incident radiation flowing through a precision aperture is absorbed. The thermal effect of the absorbed optical power is measured by comparison with the thermal effect of known electrical power. When operated in space, any TSI radiometer ages by exposure to solar UV radiation. For ageing correction, a backup radiometer is usually used, for which the UV exposure is kept low such that its ageing is negligible.
As the Sun is nearly a point source, TSI radiometers use a view-limiting mechanism to eliminate the entrance of all except direct solar radiation into the cavity. Early TSI radiometers place a large view-limiting aperture in front of a small precision aperture. In this geometry, scattering and diffraction around the edges of the view-limiting aperture increase the amount of solar power flowing through the second precision aperture. When this effect is not estimated or underestimated, it may lead to an overestimation of the TSI value as in the Earth Radiation Budget Experiment (ERBE) or in the Differential Absolute RADiometer (DIARAD).
New instruments, like the Total Irradiance Monitoring (TIM) radiometers, use an alternative geometry where the small precision aperture is put in front of the larger view-limiting aperture. In this geometry, scattering and diffraction around the edges of the precision aperture decrease the amount of solar power flowing through the view limiting aperture. When this effect is underestimated it may lead to an underestimation of the TSI.
Relative variations of the TSI in phase with the 11-year solar cycle of the order of 1 W/m² are now well established, as summarized by Dewitte & Nevens (2016) [D1] and Dewitte & Clerbaux (2017) [D2]. Apart from these true TSI variations, differences in the absolute level well above 1 W/m² are observed between the different instruments indicating limitations of the absolute accuracy. For this reason, multiplicative correction factors are determined to scale all the timeseries to a same radiometric level. These factors are determined by optimizing the consistency over the overlap periods that exist between the different instruments. Still, a reference level must be defined and this is done in this work in such a way that the average of the correction factors for the 5 most accurately calibrated instruments is set to 1.0. These 5 instruments are: Physikalisches und Meteorologisches Observatorium 06 (PMO06), Precision Monitor Sensor (PREMOS), and the TIM instruments on the Solar Radiation and Climate Experiment (TIM/SORCE), on the Total solar irradiance Calibration Transfer Experiment (TIM/TCTE), and on the International Space Station (TIM/TSIS1).
Table 1: Total Solar Irradiance space instruments (acronyms definitions in footnote). The instruments used in the C3S v3.0 and v3.1 daily TSI composite are highlighted in bold.Anchor table1 table1
Instrument 1 | Platform(s) | Used | Operation period(s) | References |
TCFM | Mariner-6 & 7 | No | 1969 | Plamondon (1969) |
ERB | Nimbus 6 | No | 1975 | Hickey et al (1976) |
Nimbus 7 | Yes | 1978 - 1993 | Hickey et al (1980) | |
ACRIM 1 | SMM | Yes | 1980-1989 | Willson et al. (1980) |
Solcon 1 | Spacelab 1 | No | 1983 | Crommelynck et al (1987) |
ERBE | ERBS | Yes | 1984-2003 | ERBE (1986) |
NOAA-9 | Yes | 1985-1989 | ||
ACRIM 2 | UARS | Yes | 1991-2001 | Willson (1994) |
Solcon 2 | Atlas 1 | No | 1992 | Crommelynck et al (1994) |
Sova 1 | Eureca | No | 1992-1993 | |
Sova 2 | Eureca | No | 1992-1993 | Romero et al. (1994) |
ISP-2 | Meteor-3 No 7 | No | 1994 | Sklyarov et al. (1996) |
DIARAD/VIRGO | SOHO | Yes | 1996-present | Dewitte et al. (2004) |
PMO06V-A/VIRGO | SOHO | Yes | 1996-present | Froehlich et al. (1997) |
ACRIM 3 | ACRIMSAT | Yes | 2000-2014 | Willson et al. (2003) |
TIM | SORCE | Yes | 2003-2020 | Kopp et al. (2005) |
DIARAD/SOVIM | ISS | No | 2008 | Mekaoui et al. (2010) |
SIM | FY 3A | No | 2008-2015 | Fang et al. (2014) |
SOVA | Picard | Yes | 2010-2014 | Dewitte et al. (2013a) |
PREMOS | Picard | Yes | 2010-2014 | Schmutz et al. (2012) |
SIM | FY 3B | No | 2011-present | Fang et al. (2014) |
TIM | TCTE | Yes | 2013-2019 | Kopp et al. (2016) |
SIM | FY 3C | No | 2013-present | Wang et al. (2017) |
TIM | TSIS-1 | Yes | 2018- present | Kopp, G. (2020), |
CLARA | NorSat | No | 2018- present | Walter et al. (2017) |
DARA | PROBA-3 | No | To be launched |
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This section describes the various daily TSI records used as input to create the C3S composite. In subsection 2.1, we start with the presentation of two different reconstruction models for the TSI: the Spectral And Total Irradiance REconstructions (SATIRE-S) and the Naval Research Laboratory’s solar variability models for Total Solar Irradiance, version 2 (NRLTSI2). These models are used for the quality check of the input satellite records. Then, subsection 2.2 presents and discusses the 12 input satellite records.
The TSI exhibits large day-to-day variations. The downward spikes in the daily mean values are due to the passage of dark sunspots, temporarily decreasing the TSI values. This is called the sunspot deficit effect. For this reason, it is often interesting to show the 121-day running mean curve. This curve is obtained by replacing the daily TSI value by the average of the daily TSI from 60 days before until 60 days after (thus 121 days in total). The 121-day running mean shows the general increase of the TSI with solar activity due to the increase of long-living bright faculae during high solar activity periods. This is called the facular excess effect.
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It is possible to estimate the TSI as a regression against proxies coming from Sun observations such as the Sunspot number. Currently, the most used regression model is: the version 2 of the Naval Research Laboratory’s (NRL) solar variability models for Total Solar Irradiance (NRLTSI2, Coddington et al., 2015, 2016). This dataset is the official daily TSI record of the NOAA CDR program. A semi-empirical approach is also possible, as in the SATIRE-S model (Yeo et al., 2014a and 2014b). Specifically, SATIRE-S derives the distribution of the magnetic features on the solar surface from full-disc solar magnetograms and continuum images, whereby the brightness of these various features is computed using a radiative transfer code from the corresponding semi-empirical solar model atmospheres. In that sense, the TSI variability in SATIRE-S is actually independent of TSI measurements. There are different uses of the SATIRE-S and NRLTSI2 models in this ATBD:
• They are used for the quality check of the 12 individual timeseries (Section 2.2), in particular to check the record’s temporal stability and, for some records, define observation periods to be excluded from the composite (usually at beginning or end of mission). The models can also help in detecting outliers in early instruments timeseries.
• The SATIRE-S model is used to interpolate short gaps (up to a maximum of 50 consecutive days) that exist in some of the individual timeseries. The gap filling method is described in Section 3.3.
• The SATIRE-S TSI model is finally ingested directly at the very beginning of the CDR, from 01.01.1979 to 06.11.1981. Indeed, before 07.11.1981 the ACRIM1 and the ERB/NIMBUS-7 observations appear significantly overestimated in comparison with the models. Keeping these first months in the C3S record is important for some users or services such as the Satellite Application Facility on Climate Monitoring (CM SAF) that provides products starting on 01.01.1979.
• The NRLTSI2 record is explicitly not used when constructing the C3S v3.0 and v3.1 daily TSI composites, so it can be used as independent source for the validation (see methodology and results in PQAD [D3] and PQAR [D5] documents).
2.1.1 SATIRE-S
The SATIRE-S (Spectral And Total Irradiance Reconstructions, Yeo et al, 2014a and 2014b) is a reconstruction of the TSI over the 1974-present-day period using full-disc magnetograms and continuum images of the Sun. It uses the data from the National Solar Observatory Photospheric magnetogram (NSO KP) (1974-1999), SOHO/ Michelson Doppler Imager (MDI) (1999-2009) and Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) (since 2010). These observations allow for the estimation of the fractional coverage of: quiet Sun, sunspot umbrae, sunspot penumbrae, faculae and network. A regression between these indices and the TSI is then derived and used in the reconstruction. The SATIRE-S data starts on 23rd August 1974 and provides data until 8th July 2023 (at time of writing). New data are regularly added to the timeseries.
SATIRE-S | ||||||||
Full name: Spectral And Total Irradiance Reconstructions | ||||||||
Organization: Max-Planck-Institut für Sonnensystemforschung (MPI for Solar System Research) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
23.08.1974 – 08.07.2023 | 01.01.1979 – 06.11.1980 | Set to 1.00015 | ||||||
Data availability | C3S Data availability (filled) | C3S estimated noise level | ||||||
100% | 100% (100%) | Set to 0.5 W/m² | ||||||
Figure 1: SATIRE-S daily TSI values (grey) and 121-days running mean (horizontal line at 1360.75 W/m² to illustrate the change in solar minima). | ||||||||
DATA SOURCE: http://www2.mps.mpg.de/projects/sun-climate/data_body.html | ||||||||
References: Yeo et al. (2014a), Yeo et al. (2014b). | ||||||||
Notes:
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2.1.2 NRLTSI2
NRLTSI2 is the version 2 of the Naval Research Laboratory’s (NRL) solar variability models for Total Solar Irradiance (TSI). This CDR was created at the Space Science Division of the Naval Research Laboratory (NRL) in collaboration with the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado. The NRLTSI2 CDR is published as part of the NOAA CDR Program and is documented by Coddington et al. (2015, 2016). In this model, the daily TSI is estimated from the observation of the bright faculae and the dark sunspots on the solar disk. A linear regression between these proxies of solar activity and the TIM/SORCE TSI was established and used in the reconstruction. The model assumes a quiet Sun TSI of 1360.45 W/m² (Kopp and Lean, 2011) as estimated from the TIM/SORCE measurement at solar minimum. The reconstruction starts on 1st January 1882 and provides data until 31st December 2022 (at time of writing). New data are regularly added to the timeseries, on a quarterly basis.
NRLTSI2 | ||||||||
Full name: Naval Research Laboratory Total Solar Irradiance version 2 | ||||||||
Organization: U.S. Naval Research Laboratory | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
01.01.1882 – 31.12.2022 | Not used in the composite | (not applicable) | ||||||
Data availability | C3S Data availability (filled) | C3S estimated noise level | ||||||
100% | 100% (100%) | (not applicable) | ||||||
Figure 2: NRLTSI2 daily values (grey) and 121-days running mean (horizontal line at 1360.45 W/m² to illustrate the stability of the solar minima). Only data onward of 1976 are shown. | ||||||||
DATA SOURCE: | ||||||||
References: Coddington et al. (2015), Coddington et al. (2016). | ||||||||
Notes:
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2.1.3 SATIRE-S / NRLTSI2 intercomparison
Figure 3 shows the SATIRE-S and NRLTSI2 timeseries over the 1975 – 2022 time period. The 2 models show very close agreement over solar cycle 23 (1996 – 2008) but otherwise exhibit significant differences, especially in the level of the solar minima in 1986, 1996 and 2019.
Anchor figure3 figure3
Figure 3: Timeseries of SATIRE-S (red) and NRLTSI2 (black) TSI reconstruction models after 121-days running mean. The daily NRLTSI2 values are shown in grey. Horizontal line at 1360.75 W/m² illustrates the change in solar minima.
Anchor section2-2 section2-2
2.2 TSI timeseries
| section2-2 | |
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Summaries of the 12 instruments used for the C3S daily TSI composite are shown in following tables. Each table specifies the full name, organization responsible of the data/instrument, period of time in which the TSI data is available and period of time used in the C3S composite. The percentages of data availabilities are provided for the original record, as well as after gap filling. The C3S adjustment factor and noise level are also provided (see Sections 3.1 and 3.2). An illustration of the original data is shown, the source of the original data is provided and notes specific to each instrument are listed, including identified “outliers” for some input timeseries.
Note about the graphs in Figure 4 to Figure 15 : the graphs show the timeseries of the satellite record (in green the daily and orange the 121-days running mean) after rescaling to the C3S record (in black). The NRLTSI2 data is also shown (in brown) after a rescaling on the same overlap period. The parts of the satellite record which are discarded in the C3S composite are in red (daily) and blue (121-days running mean).
2.2.1 ERB on NIMBUS7
ERB on Nimbus 7 | ||||||||
Full name: Earth Radiation Budget on NIMBUS7 | ||||||||
Organization: NASA / NOAA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.11.1978 – 13/12/1993 | 01.01.1981 – 31.12.1989 | 0.992447 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
83.24% | 89.45% (100% ) | 0.318 W/m² | ||||||
Figure 4: (rescaled) ERB timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
References: Hickey et al. (1980) | ||||||||
Notes:
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2.2.2 ACRIM1 on SMM
ACRIM1 on SMM | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on Solar Maximum Mission | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.02.1980 – 14.07.1989 | 07.11.1980 – 14.07.1989 | 0.995568 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
90.14 % | 90.00% (97.96%) | 0.270 W/m² | ||||||
Figure 5: (rescaled) ACRIM1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 2 : http://acrim.com/RESULTS/data/acrim1/acrim1_hdr.rtf | ||||||||
References : Willson et al. (1981) | ||||||||
Notes:
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2.2.3 ERBS
ERBS | ||||||||
Full name: Earth Radiation Budget Satellite solar monitor | ||||||||
Organization: NOAA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
17.12.1984 – 23.04.2003 | 02.07.1987 - 06.02.2001 | 0.997149 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
98.46% | 97.93% ( 100%) | 0.270 W/m² | ||||||
Figure 6: ERBS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 3 : An application, such as FileZilla, WinSCP or Wget, might be needed to open FTP sites.: ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_IRRADIANCE/ERBS2003.TXT | ||||||||
References: ERBE (1986) | ||||||||
Notes:
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2.2.4 ACRIM2
ACRIM2 | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on Upper Atmosphere Research Satellite | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
04.10.1991 – 05.05.2001 | 04.10.1991 – 05.05.2001 | 0.997821 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
93.35% | 93.35% (100%) | 0.215 W/m² | ||||||
Figure 7: (rescaled) ACRIM2 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 4 : http://acrim.com/RESULTS/data/acrim2/dayu2deg_ts_0110041651_hdr.txt | ||||||||
References: Willson (1994) | ||||||||
Notes:
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2.2.5 DIARAD / VIRGO on SOHO
DIARAD / VIRGO on SOHO | ||||||||
Full name: Differential Absolute Radiometer on Variability of Irradiance and Gravity Oscillations | ||||||||
Organization: RMIB | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
18.01.1996 - present | 01.01.1997 – present | 0.996449 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
93.95% | 93.78% (98.33%) | 0.121 W/m² | ||||||
Figure 8: (rescaled) DIARAD timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 5 : http://remotesensing.oma.be/meteo/view/en/3385923-diarad.level2.web.html | ||||||||
References: Dewitte et al. (2004) | ||||||||
Notes:
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2.2.6 PMO06 on VIRGO
PMO06 on VIRGO | ||||||||
Full name: Physikalich Meteorologisches Observatorium version 06 | ||||||||
Organization: Physikalich-Meteorologisches Observatorium Davos and World Radiation Center | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
21.02.1996 – 13.05.2022 | 01.01.1997 – 13.05.2022 | 1.000181 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
97.87% | 97.83% (98.88%) | 0.173 W/m² | ||||||
Figure 9: PMO06 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 6 : ftp://ftp.pmodwrc.ch/pub/data/irradiance/virgo/TSI/VIRGO_TSI_Daily_V8_20230728.zip | ||||||||
References: Froehlich et al. 1997 | ||||||||
Notes:
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2.2.7 ACRIM3
ACRIM3 | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on ACRIMSAT | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
05.04.2000-05.03.2013 | 05.04.2000-05.03.2013 | 1.000078 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
97.44% | 97.44% (100%) | 0.126 W/m² | ||||||
Figure 10: (rescaled) ACRIM3 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Some outliers are in red. | ||||||||
DATA SOURCE 7 : http://acrim.com/RESULTS/data/acrim3/daya2sddeg_ts4_Nov_2013_hdr.txt | ||||||||
References: Willson et al. (2003) | ||||||||
Notes:
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2.2.8 TIM on SORCE
TIM on SORCE | ||||||||
Full name: Total Irradiance Monitor (TIM) on SOlar Radiation and Climate Experiment (SORCE) | ||||||||
Organization: Laboratory for Atmospheric and Space Physics (LASP) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
25.02.2003 – 25.02.2020 | (All) | 1.000256 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
94.72% | 94.72% (96.62%) | 0.089 W/m² | ||||||
Figure 11: (rescaled) TIM/SORCE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/sorce/tsi_data/daily/sorce_tsi_L3_c24h_latest.txt | ||||||||
References : Kopp et al. (2005) | ||||||||
Notes:
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2.2.9 SOVA on Picard
SOVA on Picard | ||||||||
Full name: SOlar VAriability Experiment on Picard | ||||||||
Organization: RMIB | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
27.08.2010 – 03.11.2013 | 27.08.2010 – 03.11.2013 | 0.999345 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
80.43% | 80.43% (100%) | 0.145 W/m² | ||||||
Figure 12: (rescaled) SOVA/Picard timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://idoc-picard.ias.u-psud.fr:8182/sitools/upload/sovap-data.dat | ||||||||
Reference : Dewitte et al. (2013a) | ||||||||
Notes:
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2.2.10 PREMOS on Picard
PREMOS on Picard | ||||||||
Full name: Precision Monitor Sensor on Picard | ||||||||
Organization: Physikalich-Meteorologisches Observatorium Davos and World Radiation Center | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
27.07.2010 – 20.08.2013 | 27.07.2010 – 20.08.2013 | 1.000256 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
90.19% | 90.19% ( 100%) | 0.086 W/m² | ||||||
Figure 13: (rescaled) PREMOS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: (daily and hourly data, see note here after) | ||||||||
References : Schmutz et al. (2012) | ||||||||
Notes:
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2.2.11 TIM on TCTE
TIM on TCTE | ||||||||
Full name: Total Irradiance Monitoring on Total Solar Irradiance Calibration Transfer Experiment | ||||||||
Organization: Laboratory for Atmospheric and Space Physics (LASP) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.12.2013 – 15.05.2019 | 16.12.2013 – 15.05.2019 | 0.999771 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
83.46% | 83.46% (93.98%) | 0.092 W/m² | ||||||
Figure 14: (rescaled) TIM/TCTE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/sorce/tsi_data/daily/sorce_tsi_L3_c24h_latest.txt | ||||||||
References : Kopp et al. (2016), (TCTE 2014) | ||||||||
Notes and references:
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2.2.12 TIM on TSIS-1
TIM on TSIS-1 | ||||||||
Full name: Total Irradiance Monitor on TSIS | ||||||||
Organization: Laboratory for Atmospheric and Space Physics | ||||||||
Period covered | C3S period selected | adjustment factor | ||||||
11.01.2018 – present | 11.01.2018 – present | 0.999535 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
86.30% | 86.30% (100%) | 0.076 W/m² | ||||||
Figure 15: (rescaled) TIM/TSIS-1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/tsis/tsi_data/tsis_tsi_L3_c24h_latest.txt (version 4 is used) | ||||||||
References : Kopp (2020) | ||||||||
Notes:
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The difference in absolute scale between TSI instruments is larger than the intrinsic TSI variability. Therefore, a harmonization to remove the differences is needed. Such a harmonization has been adopted in all the previous TSI composite attempts e.g. by Dewitte and Nevens (2016)[D1], Dudok de Wit et al. (2017), Montillet et al. (2022).
In this work, single correction factors are determined for each of the 12 instruments. The 12 factors
| Mathinline |
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(α_i) |
are determined by minimizing the root mean squared difference between the corrected daily TSI for each pair of overlapping instruments, namely
| Mathdisplay |
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ε =\sqrt{\frac{\sum_{i=1}^{12}\sum_{j=1}^{i-1}\sum_{d=1.1.1979}^{31.12.2020} δ_i(d) δ_j(d)(α_i F_i (d) - α_j F_j (d) )^2 }{ \sum_{i=1}^{12}\sum_{j=1}^{i-1}\sum_{d=1.1.1979}^{31.12.2020} δ_i (d) δ_j (d) }} (Eq. 1) |
where the summations are done on all the pairs of instruments
| Mathinline |
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(i,j) |
and on all the days d in the CDR record (v3.0 CDR period : from 01.01.1979 to 31.12.2020). The delta function
| Mathinline |
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δ_i(d) |
has a value of 1 if the instrument i provides a TSI observation for the day
| Mathinline |
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F_i (d) |
, and a value of 0 otherwise 8 .
There is a total of 34 overlapping periods (average length of 1873.3 days) between the 12 input records, which is sufficient to determine the 12 unknowns
| Mathinline |
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(α_i) |
. During the minimization process, a constraint must be added to avoid that all the correction factors tend to
| Mathinline |
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ε→0 |
(as in this case the residual error
would also tends to
| Mathinline |
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α_i → 0 |
). This constraint is that the average correction factors for the TIM instruments on SORCE (i=8), TCTE (i=11) and TSIS-1 (i=12), PMO06 on VIRGO (i=6) and PREMOS on PICARD (i=10) is equal to 1, namely:
| Mathdisplay |
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\frac{α_6 + α_8 + α_{10} + α_{11} + α_{12} }{5}=1 (Eq. 2) |
The minimization is performed using a least mean square software 9 . Table 2 summarizes the obtained scaling factors
| Mathinline |
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α_i |
. The last column gives an estimate of the instruments’ precision as explained in the next section. As shown in the table, a scaling factor is also determined for SATIRE-S that is used in early months of the CDR (1979 and a large part of 1980).
Table 2 : Scaling factors and precision estimates (see Section 3.2) for the 12 input TSI timeseries.Anchor table2 table2
| Instruments | Scaling factor
(unitless) | Precision
(W/m²) | ||||||
| 1 | ERB/NIMBUS7 | 0.992447 | 318 | ||||||
| 2 | ACRIM1 | 0.995568 | 270 | ||||||
| 3 | ERBS | 0.997149 | (0.039) 0.270 | ||||||
| 4 | ACRIM2 | 0.997821 | 215 | ||||||
| 5 | DIARAD/VIRGO | 0.996449 | 121 | ||||||
| 6 | PMO06/VIRGO | 1.000181 | 173 | ||||||
| 7 | ACRIM3 | 1.000078 | 126 | ||||||
| 8 | TIM/SORCE | 1.000256 | 89 | ||||||
| 9 | SOVA/PICARD | 0.999345 | 145 | ||||||
| 10 | PREMOS/PICARD | 1.000256 | 86 | ||||||
| 11 | TIM/TCTE | 0.999771 | 92 | ||||||
| 12 | TIM/TSIS-1 | 0.999535 | 76 | ||||||
| S | SATIRE-S in 1979-1980 | 1.000150 | - |
Figure 16 shows the resulting scaled TSI records for the individual instruments. For clarity we use a 121-days running mean to remove the short term solar noise, and to highlight the instrumental differences. After scaling, the instruments agree in general quite well, except at the very beginning of the record and for 2018 onward. Figure 16 also shows that the ERBS instrument is critical to fill the so-called ACRIM gap (15.07.1989 – 03.10.1991), it is the only TSI instrument that was monitoring the TSI during this period.
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Figure 16: Timeseries of individual TSI measurements after selection and harmonization. A 121-day running mean is used to remove the short-term solar noise. The 1361 W/m² horizontal line is shown to illustrate the stability between the solar minima.
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the one of PMO06, the longest time serie) is set to 1 in a first step and the least square is performed to determine the remaining 11 free unknowns
. In a second step, all the 12 factors
(including the one that was first set to 1.0) are rescaled with a same multiplicative factor to comply with the constraint of Eq.(2). |
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The precision of the instruments is estimated by the root mean square difference with SATIRE-S, after removing the 365-days running mean for both the instrument and for the SATIRE-S. This RMS difference is given in the column ‘all’ in Table 3. This value is however dependent on the TSI variability when the instrument was operated, as illustrated by the columns ‘max’ and ‘min’ that report the same RMS difference, but respectively over the periods of high (low) solar activity. The high solar activity periods are defined as: 01.01.1984 to 31.12.1987, 01.01.1995 to 31.12.1998, 01.01.2006 to 31.12.2009, and 01.01.2017 to 31.12.2020. The periods of low solar activity are the complement.
As some instruments (PREMOS and SOVAP) have not observed during low activity periods, it is decided to use the ‘RMS max’ column as an estimation of the instrument precision. For the ERBS timeseries, the estimated precision is not realistic (due to the use of SATIRE-S in the gap filling). It is then decided to use the ACRIM1 precision as estimate for the ERBS record, as both missions used the same radiometric cavity.
Table 3: Instrument precision estimated as root mean square (RMS) difference with SATIRE-S. The columns 'max' and 'min' correspond respectively to periods of high and low solar activity. The column ‘all’ does not involve any selection based on solar activity.Anchor table3 table3
| Instruments | RMS max | RMS all | RMS min | ||
|---|---|---|---|---|---|---|
1 | ERB/NIMBUS7 | 0.318 | 0.270 | 0.263 | ||
2 | ACRIM1 | 0.270 | 0.184 | 0.128 | ||
3 | ERBS | (0.039) 0.270 | (0.037) 0.184 | (0.035) 0.128 | ||
4 | ACRIM2 | 0.215 | 0.187 | 0.139 | ||
5 | DIARAD/VIRGO | 0.121 | 0.103 | 0.064 | ||
6 | PMO06/VIRGO | 0.173 | 0.142 | 0.079 | ||
7 | ACRIM3 | 0.126 | 0.111 | 0.064 | ||
8 | TIM/SORCE | 0.089 | 0.071 | 0.035 | ||
9 | SOVA/PICARD | 0.145 | 0.145 | - | ||
10 | PREMOS/PICARD | 0.086 | 0.086 | - | ||
11 | TIM/TCTE | 0.092 | 0.073 | 0.039 | ||
12 | TIM/TSIS-1 | 0.076 | 0.057 | 0.031 |
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Many of the input records have gaps in the daily TSI values. It is the case with the ERB (Nimbus7) and ERBS (ERBE) measurements at the beginning of the composite and also of the TSIS-1 instrument at the end of the composite. In the C3S v3.0 and v3.1 daily TSI composite, a gap filling mechanism is implemented as a preprocessing of the original timeseries. A gap is filled provided it extends over less than 50 days.
The gap filling exploits the SATIRE-S reconstruction which is tuned to the observations made just before and just after the gap. In practice, the ratio between the observed TSI and the SATIRE-S reconstruction is evaluated for the last day before the data gap and for the first day following the gap. This ratio is then temporally interpolated for each day within the data gap. The TSI for this day is obtained from the SATIRE-S reconstruction corrected with this interpolated ratio. The gap filling process is illustrated in Figure 17.
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Figure 17: Illustration of the gap filling process. The black curve is an original TSI record with many data gaps (in this example the TIM/TCTE in 2014). The green curve is the SATIRE-S model. The red curve shows how the gaps can be filled by mixing the incomplete record with the (complete) SATIRE-S record.
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From the individual time series, the composite daily TSI value
| Mathinline |
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F(d) |
F(d) for the day d is constructed as the mean of the available TSI values
| Mathinline |
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F_i(d) |
weighted by the inverse of the estimated accuracy level
| Mathinline |
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\varepsilon_i |
and homogenized using the factor
| Mathinline |
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α_i |
:
| Mathdisplay |
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F(d)=\frac{\sum_{i=1}^{12} δ_i (d) \alpha_i F_i (d) \frac{1}{\mathrm{\varepsilon}_{2}^{i}} }{ \sum_{i=1}^{12} δ_i (d) \frac{1}{\mathrm{\varepsilon}_{2}^{i}} } (Eq. 3) |
where the summations are made over the 12 input instruments i.
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The method has been applied on the data described in Section 2.2. Figure 18 shows the resulting TSI composite. The grey curve is the daily value while the red curve shows the 121-days running mean. For evaluation, the 121-days running mean of the (independent) NRLTSI2 record is also shown with an offset of 0.31 W/m² to scale them to the same level.
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|---|---|---|---|---|
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Figure 18: C3S composite daily TSI values (grey) and 121-day running mean (red). The NRLTSI2 model, with an offset of 0.31 W/m² to match the curves, is shown in black.
This preliminary C3S composite of daily TSI agrees very well with the corresponding NOAA/NCEI CDR (NRLTSI2), when applying an offset of 0.31 W/m² to the latter. Close agreements are observed as well for the level of the solar minima as for the periods of high solar activity. The CDR stability and accuracy is fully addressed in the PQAD [D3] and PQAR [D5] documents.
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|---|---|---|---|---|
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Thermal effect in DIARAD/VIRGO: Since 2010, there is an annual cycle apparent in the DIARAD/VIRGO record. This is likely a thermal effect that could be better corrected using the backup cavity (contact has been taken with the DIARAD science team). In the meantime, an empirical correction has been implemented to limit this effect.
Failure of the DIARAD/VIRGO backup cavity: The aging monitoring cavity failed on 9 Oct 2017 and since then the aging is extrapolated, assuming a constant aging rate. Although “at risk”, the data is kept as it stays as long as it stays in agreement with NRLTSI2. This is justified by the small number of space instruments in the ICDR period (2021 onward).
ACRIM3 apparent aging: The ACRIM3 record shows an apparent aging with respect to the SATIRE-S and NRLTSI2 models (see Figure 10). The impact of this apparent aging on the C3S composite could be investigated.
Overlaps periods: 34 overlap periods exist between pairs of instruments. These periods are used to determine the scaling factors. A comprehensive analysis of these overlaps would be interesting to consolidate this work and possibly estimate the precision and accuracy of the instruments based on these overlaps.
Running mean software: A better handling of the missing data in the running mean software would be welcome. This will not directly impact the C3S composite timeseries but will improve the quality check of the input records.
Gap filling strategy: When there is a data gap, the data for the last day (just before the gap) and the next day (when the acquisition resumes) should be considered “at risk”, in particular because these daily TSI values may be based on only a part of the 24h. The current gap filling strategy (Section 3.3) uses the TSI from these last and next days to scale the SATIRE-S model to fill the data gap. There is therefore a high sensitivity on these “at risk” TSI observations.
SOVAP and PREMOS records on Picard satellite: These are very short records. The interest to keep them in the composite could be assessed.
TIM/TCTE in 2019: From 02.02.2019 (resumption after TIM/TCTE gap) to 15.05.2019 (end of mission) there is a decrease of the TSI that is not supported by the models and the other available observations. Investigations should be carried out to determine if these 100 days should be kept in the C3S composite.
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The output format is fully described in the Product User Guide and Specifications document [D4] for this data record. Here, only the main characteristics are provided.
Table 4: General characteristics of the C3S daily TSI composite CDR.Anchor table4 table4
General characteristics of the CDR | |
Temporal resolution | daily mean |
Time period | CDR v3.0: 1st January 1979 to 31st of December 2020 ICDR: 1st January 2021 onward v3.1: 1st January 2021 – 30th September 2023 |
Format | ASCII |
Filenames | C3S_RMIB_daily_TSI_composite_TCDR_v3.0.txt C3S_RMIB_daily_TSI_composite_ICDR_v3.1.txt |
The Total Solar Irradiance is the spectrally integrated total amount of radiant energy coming from the Sun per square meter of surface, perpendicular to the sunlight, at 1 astronomical unit.
Table 5: Total Solar Irradiance parameter.Anchor table5 table5
Total Solar Irradiance | |
long_name | Total Solar Irradiance, daily Means |
standard_name | Total Solar Irradiance |
CF_name | solar_irradiance |
units | W/m². |
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Chapman, G. A., Cookson, A. M., and Dobias, J. J. (1996): Variations in total solar irradiance during solar cycle 22, J. Geophys. Res., 101(A6), 13541– 13548, https://www.doi.org/10.1029/96JA00683.
Coddington, O., Lean J.L., Lindholm D., Pilewskie P., Snow M., and NOAA CDR Program (2015): NOAA Climate Data Record (CDR) of Total Solar Irradiance (TSI), NRLTSI Version 2. https://doi.org/10.7289/V55B00C1
Coddington, O., Lean, J.L., Pilewskie, P., Snow, M. and Lindholm, D. (2016): A solar irradiance climate data record, Bulletin of the American Meteorological Society, 97(7), pp.1265-1282. https://doi.org/10.1175/BAMS-D-14-00265.1
Crommelynck, D., Brusa, R., Domingo, V (1987): Results of the solar constant experiment onboard Spacelab-1, Solar Physics, 107, 1–9. https://www.doi.org/10.1007/BF00155336
Crommelynck, D., Domingo, V., Fichot, A., & Lee, R. (1994): Total Solar Irradiance Observations from the EURECA and ATLAS Experiments, International Astronomical Union Colloquium, 143, 63-69. https://www.doi.org/10.1017/S0252921100024544
Dewitte, S., Crommelynck, D., and Joukoff, A. (2004): Total solar irradiance observations from DIARAD/VIRGO, J. Geophys. Res., 109, A02102, https://www.doi.org/10.1029/2002JA009694
Dewitte, S., Janssen, E. and Mekaoui, S., (2013a): Science results from the SOVA-Picard total solar irradiance instrument, In AIP Conference Proceedings (Vol. 1531, No. 1, pp. 688-691) https://www.doi.org/10.1063/1.4804863
Dewitte S. (2013b): The Contribution of the DIARAD Type Radiometer to the Revision of the Solar Constant Technical Note. Available at ftp://gerb.oma.be/steven/RMIB_TSI_composite/ diaradnewsolarconstant.pdf
Dewitte, S. and Nevens, S., (2016): The total solar irradiance climate data record. The Astrophysical Journal, 830(1), p.25. https://www.doi.org/10.3847/0004-637X/830/1/25
Dewitte, S. and Clerbaux, N., (2017): Measurement of the earth radiation budget at the top of the atmosphere - a review. Remote Sensing, 9(11), p.1143. https://doi.org/10.3390/rs9111143
Dudok de Wit, T., Kopp, G., Fröhlich, C., & Schöll, M. (2017): Methodology to create a new total solar irradiance record: Making a composite out of multiple data records. Geophysical Research Letters, 44(3), 1196-1203. https://doi.org/10.1002/2016GL071866
ERBE Science Team (1986): First data from the Earth Radiation Budget Experiment. Bulletin of the American Meteorological Society, 67, 818--824. https://doi.org/10.1175/1520-0477(1986)067<0818:FDFTER>2.0.CO;2
Fang, W., Wang, H., Li, H., Wang, Y. (2014): Total Solar Irradiance Monitor for Chinese FY-3A and FY-3B Satellites: Instrument Design. Solar Physics, 289, 4711–4726. https://doi.org/10.1007/s11207-014-0595-6
Froehlich, C. (2003): Long-Term Behaviour of Space Radiometers, Metrologia,40, 60-65. https://doi.org/10.1088/0026-1394/40/1/314
Froehlich, C., Crommelynck, D.A., Wehrli, C. et al. (1997): In-Flight Performance of the Virgo Solar Irradiance Instruments on Soho. Solar Physics, 175, 267–286. https://www.doi.org/10.1023/A:1004929108864
Hickey, J.R. et al. (1976): Extra-Terrestrial Solar Irradiance Measurements from the Nimbus 6 Satellite, Proc. Joint Conference on Sharing the Sun, Winnipeg, Manitoba, Canada.
Hickey, J.R., Stowe L.L., Jacobowitz H., Pellegrino P., Machhoff R.H., House F., Vonder Haar, T.H. (1980): Initial solar irradiance determinations from Nimbus 7 cavity radiometer measurements, Science, 208, 281--283. https://www.doi.org/10.1126/science.208.4441.281
Kopp, G., Lawrence, G. & Rottman, G. (2005): The Total Irradiance Monitor (TIM): Science Results. Solar Physics, 230, 129–139. https://www.doi.org/10.1007/s11207-005-7433-9
Kopp, G. and Lean, J.L., (2011): A new, lower value of total solar irradiance: Evidence and climate significance. Geophysical Research Letters, 38(1). https://doi.org/10.1029/2010GL045777
Kopp, G. (2016): Magnitudes and timescales of total solar irradiance variability. J. Space Weather Space Clim, 6, A30. https://doi.org/10.1051/swsc/2016025
Kopp, G. (2020): TSIS TIM Level 3 Total Solar Irradiance 24-hour Means, version 03, Greenbelt, MD, USA: NASA Goddard Earth Science Data and Information Services Center (GES DISC), https://doi.org/10.5067/TSIS/TIM/DATA306
Lee, R. B., Gibson, M. A., Wilson, R. S., and Thomas, S. (1995): Long-term total solar irradiance variability during sunspot cycle 22, J. Geophys. Res., 100(A2), 1667 – 1675, https://doi.org/10.1029/94JA02897
Mekaoui, S., Dewitte, S. (2008): Total Solar Irradiance Measurement and Modelling during Cycle 23. Solar Physics, 247, 203–216. https://doi.org/10.1007/s11207-007-9070-y
Mekaoui, S., Dewitte, S., Conscience, C. and Chevalier, A. (2010) : Total solar irradiance absolute level from DIARAD/SOVIM on the International Space Station. Advances in Space Research, 45(11), pp.1393-1406. https://doi.org/10.1016/j.asr.2010.02.014
Montillet, J. P., Finsterle, W., Kermarrec, G., Sikonja, R., Haberreiter, M., Schmutz, W., & Dudok de Wit, T. (2022): Data Fusion of Total Solar Irradiance Composite Time Series Using 41 Years of Satellite Measurements. Journal of Geophysical Research: Atmospheres, 127(13), e2021JD036146. https://doi.org/10.1002/essoar.10508721.2
Mount Wilson Observatory (2013): The 150-foot Solar Tower Current Selected Data (Mt. Wilson, CA: Mount Wilson Institute), http://obs.astro.ucla.edu/150_data.html
Plamondon, (1969): TCFM solar observations on Mariner 6, JPL Space Program Summary, 3, 162.
Powell, M.J.D. (1964): "An efficient method for finding the minimum of a function of several variables without calculating derivatives". Computer Journal. 7 (2): 155–162. https://doi.org/10.1093/comjnl/7.2.155
Romero, J., Wehrli, C. & Fröhlich, C. (1994): Solar total irradiance variability from SOVA 2 on board EURECA. Solar Physics, 152, 23–29, https://doi.org/10.1007/BF01473178
Schmutz W., Fehlmann A., Finsterle W., Kopp G., Thuillier G. (2012): Total solar irradiance measurements with PREMOS/Picard, AIP Conf. Proc, 1531, 624. https://doi.org/10.1063/1.4804847
Sklyarov, Y.; Brichkov, Y.; Vorobev, V.; Kotuma, A. (1996): The satellite borne instrument Solar-Constant Gauge. Astron. Lett., 22, 318–320.
TCTE (2014): Total Solar Irradiance Calibration Transfer Experiment (Boulder, CO: Univ. of Colorado), http://lasp.colorado.edu/home/tcte/data
Walter, B., Levesque P.L., Kopp G., Andersen B., Beck I., Finsterle W., Gyo M., Heuerman K., Koller S., Mingard N., Oliva A.R., Pfiffner D., Soder R., Spescha M., Suter M.,Schmutz, W. (2017): The CLARA/NORSAT-1 solar absolute radiometer: instrument design, characterization and calibration. Metrologia, 54(5), 674. https://doi.org/10.1088/1681-7575/aa7a63
...
Instruments
...
Year Launched
...
TSI Level Solar
*Minimum (W/m²)*
...
TIM/SORCE
...
2003
...
1360.5
...
DIARAD/SOVIM
...
2008
...
1362.9
...
TIM/TCTE
...
2013
...
~1361.24
...
Mean DS TT
...
1362.0 +/- 0.9
...
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...
2. Input and auxiliary data
Summary of the instruments and data used to create the C3S daily TSI composite are shown in tables hereafter. In each table the full name, organization responsible of the data/instrument, period of time in which the TSI data is available and period of time used in the TSI composite are specified. The adjustment factors used to adjust the different absolute levels of all instruments are also provided. In addition, an illustration of the original data is shown and finally the source of the original data is provided.
...
SATIRE-S
...
Full name: Spectral And Total Irradiance Reconstructions
...
Organization: Max-Planck-Institut für Sonnensystemforschung
...
Period covered
...
C3S period selected
...
Adjustment factor
...
01/01/1974 – 20/09/2020
...
Before 16/02/1980
...
1.001370
...
...
...
ERB on Nimbus 7
...
Full name: Earth Radiation Budget on NIMBUS7
...
Organization: NASA / NOAA
...
Period covered
...
C3S period selected
...
Adjustment factor
...
16/11/1978 – 13/12/1993
...
01/01/1981 – 30/12/1989
...
0.993833
...
...
DATA SOURCE: https://opendap.larc.nasa.gov/opendap/NIMBUS-7/ERB_Ch10C_TSI_NAT/nimbus7_tsi_19781116_19931213
...
ACRIM1 on SMM
...
Full name: Active Cavity Radiometry Irradiance Monitor on Solar Maximum Mission
...
Organization: NASA
...
Period covered
...
C3S period selected
...
Adjustment factor
...
16/02/1980 – 14/07/1989
...
all
...
0.996863
...
...
DATA SOURCE: Archive RMIB (data available on request)
...
ERBS
...
Full name: Earth Radiation Budget Satellite solar monitor
...
Organization: NOAA
...
Period covered
...
C3S period selected
...
Adjustment factor
...
25/10/1984 – 06/08/2003
...
after 02/07/1987
...
0.998496
...
...
...
ERBS bi-weekly data has been processed at RMIB as in Mekaoui and Dewitte (2008)
...
ACRIM2 on UARS
...
Full name: Active Cavity Radiometry Irradiance Monitor on Upper Atmosphere Research Satellite
...
Organization: NASA
...
Period covered
...
C3S period selected
...
Adjustment factor
...
04/10/1991 – 05/05/2001
...
all
...
0.999220
...
...
...
DIARAD on VIRGO
...
Full name: Differential Absolute Radiometer on Variability of Irradiance and Gravity Oscillations
...
Organization: RMIB
...
Period covered
...
C3S period selected
...
Adjustment factor
...
18/01/1996 – present
...
01/01/1997 – present
...
0.997873
...
...
...
PMO06 on VIRGO
...
Full name: Physikalich Meteorologisches Observatorium version 06
...
Organization: Physikalich Meteorologisches Observatorium Davos and World Radiation Center
...
Period covered
...
C3S period selected
...
Adjustment factor
...
22/02/1996 – 03/08/2019
...
01/01/1997 – 31/12/2017
...
0.998241
...
...
ACRIM3 on ACRIMSAT
...
Full name: Active Cavity Radiometry Irradiance Monitor on ACRIMSAT
...
Organization: NASA
...
Period covered
...
C3S period selected
...
Adjustment factor
...
05/04/2000 – 05/03/2013
...
02/07/2002 – 05/03/2013
...
1.001572
...
...
...
TIM SORCE
...
Full name: Total Irradiance Monitor SOlar Radiation and Climate Experiment (SORCE)
...
Organization: Laboratory for Atmospheric and Space Physics
...
Period covered
...
C3S period selected
...
Adjustment factor
...
25/02/2003 – 25/02/2020
...
all
...
1.001850
...
...
...
DIARAD/SOVIM
...
Full name: Solar Variability Irradiance Monitor
...
Organization: RMIB
...
Period covered
...
C3S period selected
...
Adjustment factor
...
05/04/2008 – 03/10/2008
...
all
...
1.0
...
...
...
PREMOS
...
Full name: Precision Monitor Sensor on Picard
...
Organization: Physikalich Meteorologisches Observatorium Davos and World Radiation Center
...
Period covered
...
C3S period selected
...
Adjustment factor
...
27/07/2010 – 19/08/2013
...
all
...
1.001719
...
...
DATA SOURCE: Archive RMIB (data available on request)
...
Sova - Picard
...
Full name: SOlar VAriability Experiment on Picard
...
Organization: RMIB
...
Period covered
...
C3S period selected
...
Adjustment factor
...
19/11/2010 – 01/01/2013
...
all
...
1.001152
...
...
DATA SOURCE: Archive RMIB (data available on request)
...
TIM on TCTE
...
Full name: Total Irradiance Monitoring on Total Solar Irradiance Calibration Transfer Experiment
...
Organization: Laboratory for Atmospheric and Space Physics
...
Period covered
...
C3S period selected
...
Adjustment factor
...
16/12/2013 – 15/05/2019
...
After 2015
...
1.001267
...
...
...
TIM TSIS
...
Full name: Total Irradiance Monitor on TSIS
...
Organization: Laboratory for Atmospheric and Space Physics
...
Period covered
...
C3S period selected
...
Adjustment factor
...
2018/01/11 – 2020-09-20
...
all
...
1.001084
...
...
3. Algorithms
3.1 Individual instrument timeseries
The difference in absolute scale between TSI instruments is larger than the intrinsic TSI variability.
Therefore a harmonization to remove the scale differences is needed. To this end, the methodology of Mekaoui & Dewitte (2008) has been followed. For a given instrument i with timeseries TSIi (t), it is defined an absolute scale adjustment factor ai and an adjusted timeseries ai TSIi(t). To determine the adjustment factor ai, the instrument i is compared to a reference instrument ref over a chosen reference time period. Over this time period the average adjusted TSI value <ai TSIi(t)> is made equal to the reference value <aref TSIref(t)>, from which the adjustment for the instrument I is derived:
| Mathdisplay |
|---|
a_{i} = a_{ref} \frac{<TSI_{ref}(t)>}{<TSI_{i}(t)>} |
The scale harmonized TSI time series is then constructed using a cascade of references as follows:
- As initial reference absolute value , with by definition aref = 1, we take the average of the left and right channels of the DIARAD/SOVIM instrument (Mekaoui et al, 2010) after the revision of the so-called non equivalence between electrical and optical power as in Dewitte et al (2013b). DIARAD/SOVIM has been active during 6 months on the International Space Station (ISS) in 2008. In total six DIARAD-type radiometers have flown in space; of these, DIARAD/SOVIM is the most accurate because it has the smallest thermal nonuniformity and the best shutter design. The DIARAD-type radiometer has been kept as an independent absolute radiometer, not calibrated against other radiometers, but only compared to other radiometers for validation. The DIARAD-type radiometer has been validated by comparison with the independent LASP/TRF cryogenic radiometer, with an excellent agreement within 3 ppm concerning optical power measurement (Dewitte, 2013b). In the same measurement campaign the scattering and diffraction correction of the DIARAD-type radiometer has been validated by measuring the radiometer response to an annular illumination centered on the DIARAD view limiting aperture, with an agreement with the nominal correction within 159 ppm (Dewitte 2013b). The DIARAD/SOVIM precision apertures have been calibrated by the national metrology laboratories NPL and NIST, with an accuracy of 200 ppm.
- Next the DIARAD/VIRGO TSI measurements (Dewitte et al. 2004) are adjusted to the DIARAD/SOVIM ones during their period of overlap. The resulting DIARAD/VIRGO adjustment factor is aDV=0.997873.
- The PMO6/VIRGO TSI measurements (Froehlich et al. 1997) are adjusted to the DIARAD/VIRGO ones during their period of overlap. As in (Mekaoui & Dewitte, 2008) the "exposure independent ageing" from Froehlich (2003) for the backup instrument PMO6B is not applied, but the standard ageing correction of the continuously measuring PMO6A instrument by the backup PMO6B instrument is used. The resulting ageing corrected time series is called 'PMO6B/VIRGO'. The PMO6B/VIRGO adjustment factor is aPV=0.998241.
- The ACRIM2 measurements (Willson 1994) are adjusted to the DIARAD/VIRGO ones during their period of overlap excluding the first year of DIARAD/VIRGO operation. The ACRIM2 adjustment factor is aA2=0.999220.
- The ACRIM3 (Willson 2014) are adjusted to the DIARAD/VIRGO ones during their period of overlap excluding the first two years of ACRIM3 operation. The ACRIM3 adjustment factor is aA3=1.001572.
- The TIM/SORCE measurements (Kopp et al. 2003) are then adjusted to the DIARAD/VIRGO ones during their period of overlap. The TIM/SORCE adjustment factor is aTS=1.001850.
- The Sova-Picard measurements (Dewitte et al. 2012) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The adjustment factor is aSP=1.001152.
- The PREMOS/Picard measurements (Schmutz et al. 2012) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The Premos/Picard adjustment factor is aPRE=1.001719.
- The TIM/TCTE measurements (TCTE 2014) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The adjustment factor is aTT=1.001267.
- The ERBS measurements (ERBE 1986) are adjusted to the ACRIM 2 ones during their period of overlap. As the ERBS sampling period is 14 days, and as the ERBS measurements are relatively noisy, the "denoised" ERBS version from Mekaoui and Dewitte (2008) is used. The ERBS adjustment factor is aDV=0.998496.
- The ACRIM1 measurements (Willson et al. 1981) are adjusted to the ERBS ones during their period of overlap. The ACRIM1 adjustment factor is aA1=0.996863.
- Finally the ERB/Nimbus7 measurements (Hickey et al 1980) are adjusted to the ACRIM1 ones during their period of overlap. The ERB/Nimbus7 adjustment factor is aN7=0.993833.
Figure 1 shows the resulting scale harmonized TSI measurements from the individual TSI instruments. For clarity we use a 121 day running mean to remove the short term solar noise, and to highlight the instrumental differences.
...
Figure 1. Time series of individual TSI measurements after scale harmonization. A 121-day running mean is used to remove the short-term solar noise. ERB/Nimbus 7 (1981-1990). ACRIM1 (1980–1989), ACRIM2 (1991–2001), ACRIM3 (2002–2013). DIARAD/VIRGO (1997–2020), Sova-Picard (2010–2014)., PMO6/VIRGO (1997–2018), Premos (2010–2014). TIM/SORCE (2003–2020), TIM/TCTE (2015–2020), TIM/TSIS(2018-2020).
3.2 Construction of a composite time series
3.2.1 Apparent Drift of the TIM/SORCE Instrument
Close examination of Figure 1 shows that the TIM/SORCE TSI values start lower during solar cycle 24 and end higher during solar cycle 25 than any of the independent overlapping instruments (DIARAD/VIRGO, PMO6B/VIRGO, and ACRIM3). This is highlighted in Figure 2, where we plot the (adjusted) TIM/SORCE timeseries compared to the daily composite constructed using the C3S methodology (described in this ATBD document) but discarding TIM/SORCE as input instrument. There is a good agreement at beginning of the SORCE mission (when the adjustment factor is evaluated) but later there is a progressive divergence of the two timeseries.
...
Figure 2. Timeseries of adjusted TIM/SORCE TSI (daily in green and 121-days running mean in blue) compared to the TSI composite obtained discarding TIM/SORCE instrument (black and red curves).
Figure 3 shows the difference between TIM/SORCE and this independent composite. A relatively linear temporal drift is observed over the 1/1/2004 to 31/12/2013 time period, i.e. over 10 years. The green curve shows the linear drift of 0.03 W/m²/year between 2004 and 2014. To correct this temporal drift, it is proposed to reduce the TIM/SORCE TSI by -0.03W/m²/year after 2004. For 2014 onward, the drift is less obvious to model and it is proposed to keep the correction at a constant value of -0.3 W/m².
...
Figure 3. Difference between (adjusted) TIM/SORCE and the TSI composite obtained without considering TIM/SORCE. The black curve shows the daily difference and the red the 121-days running mean difference. The green line is the proposed modelling of the drift.
As an independent evaluation of this correction, a comparison with the SATIRE-S reconstruction is provided on Figure 4 and Figure 5. Figure 4 shows the original TIM/SORCE and SATIRE-S timeseries.
...
Figure 4. TIM/SORCE (original, not corrected not adjusted) and SATIRE-S timeseries. For each one, the daily values and the 121-days running mean are shown.
Figure 5 shows the difference without and with the -0.03W/m²/year aging correction. After correction (green and blue curves), the stability remains within 0.15 W/m² (see dashed lines at -0.03 W/m² and -0.18 W/m²).
...
Figure 5. Difference between TIM/SORCE and SATIRE-S timeseries (black: daily value, red: 121-days running mean). The green (daily) and blue (121-days running mean) curves show the difference after the aging correction of the TIM/SORCE TSI. The dashed lines illustrate the stability of the aging-corrected TIM/SORCE record.
3.2.2 Discarding of Early Drift and Late Shift Periods
Instrumental effects in individual TSI instruments can mask the true solar variation. Besides the apparent TIM/SORCE drift mentioned above, we identify the following instrumental effects by intercomparison of individual TSI instrument measurements as shown in Figure 1:
- During the first 2 years of ACRIM3 operation, the TSI values are higher than those of the older DIARAD/VIRGO and PMO6/VIRGO TSI instruments, while ACRIM3 agrees well with the other instruments later on. This is illustrated in Figure 6, which shows the VIRGO measurements and the ACRIM3 measurements during the first years of ACRIM3 operation. In general, it is more likely that an instrument drifts in the beginning of its lifetime than later on. The launch and first switch-on in space is a discontinuity to which the instrument has to adapt, and which may affect the instrument's reading. Thus, an early drift of ACRIM3 is possible. In contrast, it is very unlikely that both of the seasoned DIARAD/VIRGO and PMO6/VIRGO instruments start drifting several years after their launch at the same time and with the same magnitude coinciding with the ACRIM3 launch. It thus seems likely that ACRIM3 had an early instrumental drift during its first 2 years of operation, and we discard ACRIM3 data from this period for further use.
- During the first year of VIRGO operation, the TSI values of DIARAD/VIRGO and of PMO6/VIRGO are increasing, while the TSI values measured by the older ACRIM2 and ERBS instruments remain flat. This is illustrated in Figure 7, which shows the ERBS and ACRIM2 measurements together with the VIRGO measurements during the first years of VIRGO operation. Following a similar reasoning as above, it is more likely that the VIRGO radiometers have an early drift while they are fresh in space than it would be for the seasoned ACRIM2 and ERBS radiometers to start drifting at the same time and with the same magnitude. The early increase of the VIRGO radiometers is also discussed in Froehlich (2003). It thus seems likely that the VIRGO radiometers have an early instrumental drift during their first year of operation, and we discard VIRGO data from this period for further use. The removal of the early data does not influence the absolute value, since we use DIARAD/VIRGO only as a transfer radiometer calibrated by DIARAD/SOVIM, not as an absolute radiometer.
- At the end of its lifetime, during the so-called "ACRIM gap" period in between ACRIM1 and ACRIM2, the ERB/Nimbus 7 instrument had abrupt shifts (Lee et al. 1995; Chapman et al. 1996) when comparing it to commonly used TSI regression models that reproduce the TSI variation from sunspot and facula indices (see D4). Physically it seems hard to understand how the true TSI could vary in a discontinuous way, while instrumental discontinuities can never be excluded. Also, during the ACRIM gap, the ERBE TSI was compatible with commonly used TSI regression models (Lee et al. 1995), while the ERB/Nimbus 7 TSI was not. This is illustrated in Figure 8, which shows the ERB, ACRIM1, ERBS, and ACRIM2 TSI together with a TSI proxy model—which is described in D4—for the period 1988–1994. Thus, it seems likely that the ERB/Nimbus 7 suffered from instrumental degradation during the ACRIM gap, and therefore we discard the ERB/Nimbus 7 data after 1990.
- The ACRIM1 instrument was launched on the SMM spacecraft in 1980 February. From 1980 November to 1984 April the SMM attitude control was degraded, leading to the so-called "ACRIM1 spin period" (Willson 1994). In the version 2 of the dataset ACRIM1 data is used even during the spin period as no other reliable dataset is available for the year 1980. Data used is comparable to SATIRE-S dataset.
- The ERB/Nimbus 7 did not have the capability for independent aging monitoring and correction. We only consider it as reliable when it can be compared with an independent trusted instrument, namely, ACRIM1. For v2.0 of the C3S composite data from 1981 onwards is used.
- During the solar minimum from 1984 to 1987, the ERBS instrument was fresh in space and could be subject to early drifts. By precaution we discard the ERBS data for this period, and we only rely on the older ERB and ACRIM1 instruments.
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Figure 6. 121-day running mean TSI values of DIARAD/VIRGO, PMO6B/VIRGO, and ACRIM3 for the period 2000–2006. Figure reproduced from D1.
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Figure 7. 121-day running mean TSI values of ERBS, ACRIM2, DIARAD/VIRGO, and PMO6B/VIRGO for the period 1995–2000 . Figure reproduced from D1.
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Figure 8. 121-day running mean TSI values of ERB, ACRIM1, ERBS, and ACRIM2 measurements and Mount Wilson magnetogram based regression model for the period 1995–2000. Figure reproduced from D1
Figure 9 shows the retained "quality-controlled" TSI instrument time series. These quality-controlled time series are consistent within +/−0.25 W m−2 over the entire period from 1979 to 2020, while in the original time series from Figure 1 deviations of up to 0.7 W m−2 exist.
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Figure 9. Time series of individual TSI measurements after drift correction TIM/SORCE and removal of early drift and late shift period for ERB, and removal of early drift periods for ERBS, DIARAD/VIRGO, PMO06-B/VIRGO, and ACRIM3. ERB/Nimbus 7 (1981-1990). ACRIM1 (1980–1989), ACRIM2 (1991–2001), ACRIM3 (2002–2013). DIARAD/VIRGO (1997–2020), Sova-Picard (2010–2014)., PMO6/VIRGO (1997–2018), Premos (2010–2014). TIM/SORCE (2003–2020), TIM/TCTE (2015–2020), TIM/TSIS(2018-2020).
3.2.3 Gap filling
For some of the TSI instruments, the timeseries presents frequent missing daily values over some periods. It is the case of the ERB measurements at the beginning of the composite and also of the TSIS instrument at the end of the composite. In version 2.x of the C3S daily TSI composite, a gap filling mechanism is implemented as preprocessing of the original timeseries. Gaps are filled provided they extend over less than 50 days.
The gap filling exploits the SATIRE-S reconstruction which is tuned to the observations made just before and just after the gap. In practice, the ratio between the observed TSI and the SATIRE-S reconstruction is evaluated for the last day before the data gap and for the first day following the gap. This ratio is then temporally interpolated for any day within the data gap and the TSI for this day is obtained from the SATIRE-S reconstruction corrected with this interpolated ratio.
3.2.4 Composite
From the individual time series of Figure 9, on a daily basis the composite TSI value is calculated as the mean of all available TSI values. The resulting composite is then scaled using an overall factor (
| Mathinline |
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a = 0.5 \ast \left(1+ \frac{1}{a_{TT}} \right) = 0.9993367 |
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Figure 10 shows the resulting TSI measurements; the red curve shows the daily mean values, while the green curve shows the 121-day running mean values.
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Figure 10. Composite TSI values. Red curve: daily mean TSI measurements. Green curve: 121-day running mean TSI measurements. Blue curve: 121-day running mean TSI Mount Wilson regression model.
The downward spikes in the daily mean values are due to the passage of dark sunspots, temporarily decreasing the TSI values. This is the sunspot deficit effect.
The general increase of the TSI with solar activity highlighted by the 121-day running mean values is due to the increase of long-living bright faculae during high solar activity. This is the facular excess effect.
4. Output data
The output format is fully described in the Product User Guide and Specifications document [D3] for this data record. Here, only the main characteristics are provided, as well as an illustration for each field.
4.1 General characteristics of the CDR
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General characteristics of the CDR
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Temporal resolution
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daily mean
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Time period
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TCDR: 1st January 1979 to 31st of December 2018
ICDR: 1st January 1979 to present day
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Format
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ASCII
4.2 Total Solar Irradiance
The Total Solar Irradiance is the spectrally integrated total amount of radiant energy coming from the Sun per square meter of surface, perpendicular to the sunlight, at 1 astronomical unit.
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Total Solar Irradiance
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long_name
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Total Solar Irradiance, daily Means
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standard_name
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Total Solar Irradiance
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CF_name
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solar_irradiance
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units
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W/m².
An illustration of incoming total solar irradiance is provided in Figure 11.
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Figure 11. Total Solar Irradiance composite from RMIB
References
Chapman, G. A., Cookson, A. M., and Dobias, J. J. (1996). Variations in total solar irradiance during solar cycle 22, J. Geophys. Res., 101(A6), 13541– 13548, doi:10.1029/96JA00683.
Crommelynck, D., Domingo, V., Fichot, A., & Lee, R. (1994). Total Solar Irradiance Observations from the EURECA and ATLAS Experiments. International Astronomical Union Colloquium, 143, 63-69. doi:10.1017/S0252921100024544
Crommelynck, D.; Brusa, R.; Domingo, V (1987). Results of the solar constant experiment onboard Spacelab-1. Solar Phys, 107, 1–9.
Dewitte S. (2013b). The Contribution of the DIARAD Type Radiometer to the Revision of the Solar Constant Technical Note.
Available at ftp://gerb.oma.be/steven/RMIB_TSI_composite/
diaradnewsolarconstant.pdf
Dewitte, S., Crommelynck, D., and Joukoff, A. (2004). Total solar irradiance observations from DIARAD/VIRGO, J. Geophys. Res., 109, A02102, doi:10.1029/2002JA009694.
Dewitte, S., Janssen, E. and Mekaoui, S., (2013a). May. Science results from the Sova-Picard total solar irradiance instrument. In AIP Conference Proceedings (Vol. 1531, No. 1, pp. 688-691). AIP. doi:10.1063/1.4804863
ERBE Science Team (1986). First data from the Earth Radiation Budget Experiment.BAMS, 67, 818--824.
Fang, W.; Wang, H.; Li, H.; Wang, Y. Total Solar Irradiance Monitor for Chinese FY-3A and FY-3B Satellites: Instrument Design (2014). Solar Phys, 289, 4711–4726.
Froehlich, C. (2003). Long-Term Behaviour of Space Radiometers, Metrologia,40, 60-65.
Froehlich, C., Crommelynck, D.A., Wehrli, C. et al. (1997). In-Flight Performance of the Virgo Solar Irradiance Instruments on Soho. Sol Phys 175, 267–286. doi:10.1023/A:1004929108864
Hickey, J. R. et al. (1976). Extra-Terrestrial Solar Irradiance Measurements from the Nimbus 6 Satellite, Proc. Joint Conference on Sharing the Sun, Winnipeg, Manitoba, Canada.
Hickey, J.R., L.L. Stowe, H. Jacobowitz, P. Pellegrino, R.H. Machhoff, F. House, T.H. Vonder Haar (1980). Initial solar irradiance determinations from nimbus 7 cavity radiometer measurements, Science, 208, 281--283.
Kopp, G. (2020), TSIS TIM Level 3 Total Solar Irradiance 24-hour Means, version 03, Accessed 01.10.2020 at doi:10.5067/TSIS/TIM/DATA306
Kopp, G. Solar Variability Magnitudes and Timescales (2016). J. Space Weather Space Clim, 6, A30
Kopp, G., Lawrence, G. & Rottman, G. (2005). The Total Irradiance Monitor (TIM): Science Results. Sol Phys 230, 129–139. doi:10.1007/s11207-005-7433-9
Lee, R. B., Gibson, M. A., Wilson, R. S., and Thomas, S. (1995). Long‐term total solar irradiance variability during sunspot cycle 22, J. Geophys. Res., 100(A2), 1667– 1675, doi:10.1029/94JA02897
Mekaoui, S., Dewitte, S. (2008). Total Solar Irradiance Measurement and Modelling during Cycle 23. Sol Phys 247, 203–216. doi:10.1007/s11207-007-9070-y
Mekaoui, S., Dewitte, S., Conscience, C. and Chevalier, A. (2010). Total solar irradiance absolute level from DIARAD/SOVIM on the International Space Station. Advances in Space Research, 45(11), pp.1393-1406.
Mount Wilson Observatory (2013). The 150-foot Solar Tower Current Selected Data (Mt. Wilson, CA: Mount Wilson Institute), http://obs.astro.ucla.edu/150_data.html+
Greenbelt, MD, USA: NASA Goddard Earth Science Data and Information Services Center (GES DISC),
Plamondon, (1969): TCFM solar observations on Mariner 6, JPL Space Program Summary, 3, 162.
Romero, J., Wehrli, C. & Fröhlich, C. (1994). Solar total irradiance variability from SOVA 2 on board EURECA. Sol Phys 152, 23–29 doi:10.1007/BF01473178
Schmutz W., Fehlmann A., Finsterle W., Kopp G., Thuillier G. (2012). Total solar irradiance measurements with PREMOS/Picard, AIP Conf. Proc, 1531, 624. doi: 10.1063/1.4804847
Sklyarov, Y.; Brichkov, Y.; Vorobev, V.; Kotuma, A. (1996). The satellite borne instrument Solar-Constant Gauge. Astron. Lett., 22, 318–320
...
Wang, H.; Wang, Y.; Ye, X.; Yang, D.; Wang, K.; Li, H.; Fang, W. (2017): Instrument Description: The Total Solar Irradiance Monitor on the FY-3C Satellite, an Instrument with a Pointing System
...
. Solar
...
Physics, 289, 8. https://doi.org/10.1007/s11207-016-1026-7
Willson, R.C., Gulkis S., Janssen M., Hudson H.S., Chapman G.A. (1980): Observations of Solar Irradiance Variability, Science, 211, 700 - 702. https://doi.org/10.1126/science.211.4483.700
Willson, R. (1994)
...
: Irradiance Observations of SMM, Spacelab 1, UARS, and ATLAS Experiments. International Astronomical Union Colloquium, 143, 54-
...
62. https://doi.org/10.1017/S0252921100024532
Willson, R.; Mordvinov, A. (2003) : Secular total solar irradiance trend during solar cycles 21–23
...
. Geophysical Research Letters, 30, 1199. https://doi.org/10.1029/2002GL016038
Willson, R.C. (2014)
...
: ACRIM3 and the Total Solar Irradiance database
...
. Astrophys Space Sci 352, 341–352. https://doi.org/10.1007/s10509-014-1961-4
Yeo K.L., Krivova N.A., Solanki S.K., Glassmeier K.H. (2014a): Reconstruction of total and spectral solar irradiance from 1974 to 2013 based on KPVT, SoHO/MDI and SDO/HMI observations, Astron. Astrophys., 570, A85. https://doi.org/10.1051/0004-6361/201423628
Yeo K.L., Krivova N.A., Solanki S.K. (2014b): Solar cycle variation in solar irradiance, Space Sci. Rev., https://doi.org/10.1007/s11214-014-0061-7
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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