CAMS Reanalysis data documentation

Introduction

Here we document the CAMS reanalysis dataset, which, eventually, will cover the period January 2003 to near real time (NRT), though the first tranche of data, released in November 2017, only covers the year 2003. It is planned to release the first 5 years of the CAMS reanalysis by April 2018 and the rest by the end of 2018. The CAMS reanalysis is the latest global reanalysis data set of atmospheric composition (AC) produced by the Copernicus Atmosphere Monitoring Service, consisting of 3-dimensional time-consistent AC fields, including aerosols, chemical species and greenhouse gases. The data set builds on the experience gained during the production of the earlier MACC reanalysis and CAMS interim reanalysis.

The CAMS reanalysis was produced using 4DVar data assimilation in CY42R1 of ECMWF’s Integrated Forecast System (IFS), with 60 hybrid sigma/pressure (model) levels in the vertical, with the top level at 0.1 hPa. Atmospheric data are available on these levels and they are also interpolated to 25 pressure, 10 potential temperature and 1 potential vorticity level(s). "Surface or single level" data are also available.

Generally, the data are available at a sub-daily and monthly frequency and consist of analyses and 48h forecasts, initialised daily from analyses at 0 UTC.

The data are archived in the ECMWF data archive (MARS) and can be retrieved using the ECMWF Public Dataset service via the WebAPI (Member State users can access the data using MARS directly, in the usual manner). In the future, the data will be available from the CAMS data server.

The IFS model and data assimilation system

The 4DVar data assimilation uses 12 hour windows from 09 UTC to 21 UTC and 21 UTC to 09 UTC (the following day).

The IFS model documentation for various model cycles can be found on https://www.ecmwf.int/en/forecasts/documentation-and-support/changes-ecmwf-model/ifs-documentation. The model used in the CAMS reanalysis includes several updates to the aerosol and chemistry modules on top of the standard CY42R1 release.

Aerosol model

• The aerosol model contains new aerosol optical properties (see Bozzo et al. 2017: "Implementation of a CAMS-based aerosol climatology in IFS" ECMWF Technical memo).
• For Organic Matter (OM), there is significantly less extinction per mass.
• Aerosol optical properties at 10 micron wavelength
• Bugfix of dust and sea-salt sedimentation
• Decrease of the fraction of sea-salt aerosol subjected to in-cloud scavenging from 0.7 to 0.2 (to compensate the low bias brought by the activation of sedimentation)
• SO2 dry deposition velocities from SUMO (same as SO2 in chemistry)
• Secondary Organic Aerosol (SOA) production scaled on non biomass burning CO emissions
• SO2 to SO4 conversion complexified: a temperature dependency was added; conversion increased by 50% where relative humidity > 98% and T> 273.15 K
• SO2 to SO4 conversion e-folding time was decreased from 8 to 4 days at the equator and from 3 to 0.5 days at the pole
• SO4 dry deposition velocity was ncreased over the oceans
• Use of mass fixer for aerosol species
• Scaling of biomass-burning Black Carbon (BC) emissions using the ratio of BC AOD (CAMS interim reanalysis) / BC AOD (CAMS interim control run). Not done for OM because of the change in optical properties.
• 80% of SO2 emissions are released in the two lowest model levels (as an update of tendencies) rather than at surface (fluxes)
• Use of an external file to define the altitude of ~1500 volcanoes. Where there is a volcano, SO2 emissions are released 3 model levels higher than the altitude of the volcano.

Chemistry mechanism

The chemical mechanism of the IFS is an extended version of the Carbon Bond 2005 (CB05) chemical mechanism as implemented in CTM Transport Model 5 (TM5). In the CAMS reanalysis the model as documented in Flemming et al. (2015) and Flemming et al. (2017) is used with the following updates:

• Update of heterogeneous rate coefficients for N2O5 and HO2 based on clouds and aerosol
• Modification of photolysis rates by aerosol
• Dynamic tropopause definition based on T profile for coupling to stratosphere and tropospheric mass diagnostics
• Monthly mean VOC emissions calculated by the MEGAN model using MERRA reanalysed meteorology (Sindelarova et al., 2014) for all VOCs and for whole period 2003-2015 period.
• Bugfixes, in particular for diurnal cycle of dry deposition whose correction has decreased ozone dry deposition (about 15-20%)     
• CHEM_VER=15

Greenhouse Gases

The model configuration for greenhouse gases is based on the specification of the following components documented in the listed papers below:

• Emissions for CO2 are documented in Agusti-Panareda et al. (2014), Massart et al. (2016).
• Bias correction for CO2 ecosystem fluxes based on the Biogenic Flux Adjustement Scheme is documented by Agusti-Panareda et al. (2016)
• Emissions and loss rate for CH4 is documented in Massart et al. (2014)
• Mass fixer configuration for CO2 and CH4 is documented by Agusti-Panareda et al. (2017)

Emission datasets

The emissions datasets used to produce the CAMS reanalysis are listed in Table 1. They include the MACCity anthropogenic emission, GFAS fire emissions, MEGAN biogenic emissions and several GHG emission datasets.

Table 1: Emission datasets used in the CAMS reanalysis

Data organisation

The data can be accessed using the MARS keywords class=mc and expver=eac4 (or ‘dataset’ : “eac4” for the ECMWF Public Dataset service via the WebAPI). Subdivisions of the data are labelled using stream, type and levtype.

Stream:

• oper: sub-daily
• mnth: synoptic monthly means
• moda:monthly means of daily means

Type:

• an: analyses
• fc: forecasts

Levtype:

• sfc: surface or single level
• pl: pressure levels
• pt: potential temperature levels
• pv: potential vorticity level
• ml: model levels

Spatial grid

The CAMS reanalysis data have a resolution of 80km. The data are available either as spectral coefficients with a triangular truncation of T255 or on a reduced Gaussian grid with a resolution of N128. These grids are so called "linear grids", sometimes referred to as TL255.

Temporal frequency

For sub-daily data for the CAMS reanalysis (stream=oper) the analyses (type=an) are available 3-hourly. The daily forecast, run from 0 UTC, has 3-hourly steps from 0 to 48 hours for the 3D model level and pressure level fields, and hourly steps from 0 to 48 hours for the surface fields.

Monthly means

Several parameters are also available as synoptic monthly means, for each particular time and forecast step (stream=mnth) and as monthly means of daily means, for the month as a whole (stream=moda).

Monthly means for analyses and instantaneous forecasts are created from data with a valid time in the month, between 00 and 23 UTC, which excludes the time 00 UTC on the first day of the following month. Monthly means for accumulations and mean rates are created from data with a forecast period falling within the month. For example, monthly means of daily means for accumulations and mean rates are created from contiguous data with forecast periods spanning from 00 UTC on the first day of the month to 00 UTC on the first day of the following month.

Data format

Model level fields are in GRIB2 format. All other fields are in GRIB1, unless otherwise indicated.

Level listings

Pressure levels: 1000/950/925/900/850/800/700/600/500/400/300/250/200/150/100/70/50/30/20/10/7/5/3/2/1

Potential temperature levels: 300/315/320/330/350/370/395/475/600/850

Potential vorticity level: 2000

Model levels: 1/to/60, which are described at https://www.ecmwf.int/en/forecasts/documentation-and-support/60-model-levels.

Parameter listings (This still needs to be worked on)

Tables 2-? below describe the surface and single level parameters (levtype=sfc), ....

Table 2: Monthly means of total column fields (Stream=moda/mnth).

Table 3: Monthly means of pressure level fields (Stream=moda/mnth) and fields on lowest model level (i.e. fields on model level 60).

Satellite Data

The atmospheric composition satellite retrievals used as input into the CAMS reanalysis are listed below. The following abbreviations are used in Table 1. TC: Total column, TRC: Tropospheric column, PROF: profiles, PC: Partial columns, ColAv: Column average mixing ratio, QR= quality flag given by data providers, SOE: Solar elevation, MODORO: Model orography, PRESS_RL= pressure at bottom of layer, LAT: Latitude.

Table 1: Satellite retrievals of atmospheric composition that were assimilated in the CAMS reanalysis

Control run (perhaps remove this for now)

In parallel to the CAMS reanalysis a control run without data assimilation was run that covers the same period as the CAMS reanalysis. This control run uses the same model configuration as the CAMS reanalysis and is made up of 24h long cycling forecasts from 0 UTC. The meteorological initial fields at 0UTC were always taken from the CAMS reanalysis. Comparing the CAMS reanalysis with the control run allows us to identify the impact of the data assimilation.

The control run is available from MARS or WebAPI using expver=gqk3, stream=oper, type=fc.

Guidelines

The following advice is intended to help users understand particular features of the CAMS reanalysis data:

• Users who want to use meteorological data only are advised to use the ERA5 meteorological reanalysis.

Known issues

At the time of writing (2017-10) we are aware of these issues with the CAMS reanalysis:

This list will be updated as we become aware of further issues in the CAMS reanalysis.

How to cite the CAMS Reanalysis

Please acknowledge the use of the CAMS reanalysis as stated in the Copernicus C3S/CAMS License agreement:

• "Where the Licensee communicates to the public or distributes or publishes CAMS Information, the Licensee shall inform the recipients of the source of that information by using the following or any similar notice:

  'Generated using Copernicus Atmosphere Monitoring Service Information [Year]'.

• Where the Licensee makes or contributes to a publication or distribution containing adapted or modified CAMS Information, the Licensee shall provide the following or any similar notice:

  'Contains modified Copernicus Atmosphere Monitoring Service Information [Year]';

Any such publication or distribution shall state that "neither the European Commission nor ECMWF is responsible for any use that may be made of the information it contains."

References

CAMS reanalysis references will be available from the ECMWF e-Library.

Related articles

• Page:
  CAMS: Global atmospheric composition forecast data documentation
• Page:
  CAMS Regional: European air quality reanalyses data documentation
• Page:
  CAMS global biomass burning emissions based on fire radiative power (GFAS): data documentation
• Page:
  CAMS solar radiation time-series: data documentation
• Page:
  CAMS User Support Journey