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Introduction
Here we document the ERA5-Land dataset, which, eventually, will cover the same period as ERA5, January 1950 to near real time (NRT). ERA5-Land data released so far covers the period from 1981 to 2-3 months before the present. The back-extension from 1950 will start production in late 2019 with the release planned for Q2-Q3 2020. In addition, the facility to deliver timely updates is being implemented and it will be made available shortly. ERA5-Land timely updates (hereafter called ERA5-LandT) will be synchronized with the timely updates of the ERA5 climate reanalysis (ERA5T).
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Currently, the data can only be downloaded on a regular latitude/longitude grid of 0.1°x0.1° via the CDS catalogue. In the near future the data will also be made available in the native grid.
Land Surface Model
H-TESSEL is the land surface model that is the basis of ERA5-Land. The H-TESSEL version used in the production of ERA5-Land corresponds to that of the IFS model documentation CY45R1.
Data organisation and access
The data are archived in the ECMWF data archive (MARS) and the data have been copied to the Climate Data Store (CDS). The data should be downloaded using the CDS catalogue or the CDS API, which can obtain data from the CDS copy or from MARS (Member State users can access the data using MARS directly, in the usual manner). Documentation on how to use the CDS API to download ERA5-Land data can be found here. The installation and downloading steps are similar to those of ERA5.
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CDS date time | MARS date time step | CDS date time | MARS date time step | |
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date 00 | date-1 0 24 | date 12 | date 0 12 | |
date 01 | date 0 1 | date 13 | date 0 13 | |
date 02 | date 0 2 | date 14 | date 0 14 | |
date 03 | date 0 3 | date 15 | date 0 15 | |
date 04 | date 0 4 | date 16 | date 0 16 | |
date 05 | date 0 5 | date 17 | date 0 17 | |
date 06 | date 0 6 | date 18 | date 0 18 | |
date 07 | date 0 7 | date 19 | date 0 19 | |
date 08 | date 0 8 | date 20 | date 0 20 | |
date 09 | date 0 9 | date 21 | date 0 21 | |
date 10 | date 0 10 | date 22 | date 0 22 | |
date 11 | date 0 11 | date 23 | date 0 23 |
Spatial grid
The ERA5-Land HRES dataset has been produced at a resolution of 9 km, (~0.08°) and in a (octahedral) reduced Gaussian grid (represented as TCo1279). Currently, the uncertainty of the fields is to be obtained from the ERA5 EDA dataset, which has a resolution of 62km (~0.56°).
The article "Model grid box and time step" might be useful.
Temporal frequency
For sub-daily data for the HRES (stream=oper) the parameters labelled as analyses (type=an) are available hourly. The once daily short forecasts, run from 00 UTC, also provide data hourly, with steps from 01 to 24. The uncertainty is currently provided by ERA5 EDA fields, which are available every 3 hours for the surface fields.
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Please, note that the convention for accumulations used in ERA5-Land differs with that for ERA5. The accumulations in the short forecasts of ERA5-Land (with hourly steps from 01 to 24) are treated the same as those in ERA-Interim or ERA-Interim/Land, i.e., they are accumulated from the beginning of the forecast to the end of the forecast step. For example, runoff at day=D, step=12 will provide runoff accumulated from day=D, time=0 to day=D, time=12. The maximum accumulation is over 24 hours, i.e., from day=D, time=0 to day=D+1,time=0 (step=24).
- HRES: accumulations are from 00 UTC to the hour ending at the forecast step
- For the CDS time, or validity time, of 00 UTC, the accumulations are over the 24 hours ending at 00 UTC i.e. the accumulation is during the previous day
- Synoptic monthly means (stream=mnth): accumulations have units of "variable_units per forecast_step hours"
- Monthly means of daily means (stream=moda): accumulations have units that include "per day", see section Monthly means
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In addition to the sub-daily data, all ERA5-Land parameters are also available as monthly means. Monthly means are available in two forms:
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- The hydrological parameters are in units of "m of water equivalent per forecast_step hours" and so they should be multiplied by 1000 to convert to kgm-2 per forecast_step hours or mm per forecast_step hours.
- The energy (turbulent and radiative) and momentum fluxes should be divided by 60 x 60 x fc_step to convert to the units of Wm-2 and Nm-2, respectively.
Data format
Surface fields in ERA5-Land are encoded either in GRIB1 or GRIB2 format. Tables 1 and 2 indicate the format for all parameters in ERA5-Land. Note that the retrieval of the data in NetCDF format is still possible via the CDS.
The article "What are GRIB files" might be helpful.
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Tables 1 and 2 below describe the surface parameters available in ERA5-Land (levtype=sfc). Information on all ECMWF parameters is available from the ECMWF parameter database.
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Accumulations are described in section 140385203. The accumulations in monthly means (stream=moda/mnth) are described in section monthly means
How to use lake-related fields
Independently whether a model grid point is over a lake or not, the IFS computes lake variables all over the globe, at each grid-box. This is to ease output field aggregation at diverse model resolutions and to have a warm start of the model with shorter spin-up time if lake cover is upgraded, i.e., it is still a decent lake initial condition if lake location are updated or a new lake is added operationally. Lake depths (input parameter for our lake parametrization) are specified for each grid-box either with in-situ values or with a default 25 m value; over ocean we use ocean bathymetry. Worth to mention that the later default values will be changed soon (extra information in this HESS reference). The computed lake variable values are not taken into account in the total grid-box flux calculations if lake is not present in the grid-box.
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The ECMWF model also contains an ice module, a snow module and a bottom sediments module. The present setup of the IFS is running with no bottom sediment and snow modules (snow accumulation over ice is not allowed and snow parameters are used only for albedo purposes). In the implementation in the IFS lake ice can be fractional within a grid-box with inland water (10 cm of ice means 100 % of a grid-box or tile is covered with ice; 0 cm of ice means 100 % of the grid-box is covered by water; in between a linear interpolation is applied) (Manrique-Sunen et al., 2013). At present, the water balance equation is not included for lakes and the lake depth and surface area are kept constant in time (IFS Documentation, 2017, chapter 8 and 11 ). Lake parametrization also requires the lake fraction CL, lake depth DL (preferably bathymetry), and lake initial conditions. DL is the most important external parameter that uses the lake parametrization.
Known issues
Three components of the total evapotranspiration have values swapped as follows:
- variable "Evaporation from bare soil" (mars parameter code 228101 (evabs)) has the values corresponding to the "Evaporation from vegetation transpiration" (mars parameter 228103 (evavt)),
- variable "Evaporation from open water surfaces excluding oceans (mars parameter code 228102 (evaow)) has the values corresponding to the "Evaporation from bare soil" (mars parameter code 228101 (evabs)),
- variable "Evaporation from vegetation transpiration" (mars parameter code 228103 (evavt)) has the values corresponding to the "Evaporation from open water surfaces excluding oceans" (mars parameter code 228102 (evaow)).
How to cite ERA5-Land
Please acknowledge the use of ERA5-Land as stated in the Copernicus C3S/CAMS License agreement:
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Dataset citable as: Copernicus Climate Change Service (C3S) (2019): C3S ERA5-Land reanalysis . Copernicus Climate Change Service, date of access. https://cds.climate.copernicus.eu/cdsapp#!/home
References
Further ERA5-Land references and related information are available from the ECMWF e-Library.
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