ERA5 Gaussian Grid
Introduction
ERA5 is a climate reanalysis dataset developed through the Copernicus Climate Change Service (C3S) with the raw-data processed and delivered by ECMWF. The dataset is the successor to the popular ERA-Interim dataset - which is now discontinued by end-of year 2019. The ERA5 dataset has several improvements compared to ERA-Interim:
- Newer modelling system
- More observations used in the assimilation
- Higher spatial horizontal resolution (around 31 km compared to 79 km)
- Higher spatial vertical resolution
More information is available in the windPRO Online Data release note from August 2017. A first comparison to ERA-Interim and MERRA2 is also included in this note - see here.
ERA5 and EMD-WRF Mesoscale Services
EMD has incorporated the ERA5 data in to its EMD-WRF on-demand setup and its pre-run datasets. Read more here: <here>. A thorough validation of ERA5 in a EMD-WRF modelling context has been conducted and included in two technical notes covering EMD-WRF On-Demand services and EMD-WRF Europe+ pre-run mesoscale dataset.
Resolution, Coverage and Evaluation
Resolution:
The native model grid is a reduced gaussian grid (T620) which has a lateral resolution of 0.28125° (around 31 km). It holds hourly values. Coverage is global for land-areas and coastal regions. In windPRO, offshore coverage is expected to cover a distance of approximately 300 km from the coastline.
First ERA5 Data Evaluation:
The hourly wind speeds from ERA5 and MERRA2 data have been compared to measured wind speeds from 108 tall meteorological masts around the globe. The masts have sensor heights ranging from about 60m to 140m. Correlations have been calculated for all sites - and ERA5 data shows a significant improvement over MERRA2 – the average correlation is increased by 0.07 and the variation is also lower. Further information in the release note, here.
Additional Data Evaluations:
In connection evaluations of the accuracy of the EMD-WRF mesoscale data products, the raw MERRA2 and raw ERA5 reanalysis data has also been included in the reporting: The results is found in two evaluation reports - one on the EMD-WRF On-Demand product and on on our EMD-WRF Europe+ dataset. ERA5 performance is consistent and high when benchmarking against local meteorological towers. Please consult the reports here for more details:
Release Schedule and Available Years
The release of then ERA5 data has been made in batches following a schedule from C3S and ECMWF. The first batch of data covered the period of 2010-2016. It was released during summer 2017. In December 2017 ECMWF started monthly updates of ERA5 so that oneward data from a new month is added every month with a 2-3 month delay. In its archives - windPRO holds data back to 1988 (i.e. more than 30 years of data). EMD will release ERA5 in windPRO as soon as it is available, but be aware that data is released (from ECMWF) with a delay of about three months. You can always find the ECMWF release plan here: <https://climate.copernicus.eu/products/climate-reanalysis>
Known Issues
2018-12-06:
Issue: Copernicus support notified users that ERA5 data downloaded throught the climate data store (CDS) was affected by an error in the u- and v components of the pressure level winds (https://confluence.ecmwf.int/pages/viewpage.action?pageId=127305868)
Solution: ERA5 data in windPRO are not influenced by this problem: We are (currently) procuring data directly from ECMWF (and not the CDS) - and also distributing physical heights of 10m and 100m.
Data Parameters
EMD extracts a focused subset of climate-parameters from the ERA5 datasets - this subset focuses on wind-energy modelling. When the data have been processed at EMD, then the following parameters are available from within the online-data services within windPRO.
| Parameter | Unit | Description |
|---|---|---|
| time | UTC time stamp | |
| wSpeed.10 | m/s | Wind speed @ 10m |
| wDir.10 | deg | Wind direction @ 10m |
| wSpeed.10n | m/s | Neutral wind speed @ 10m |
| wDir.10n | deg | Neutral wind direction @ 10m |
| wSpeed.100 | m/s | Wind speed @ 100m |
| wDir.100 | deg | Wind direction @ 100m |
| temperature.2 | deg.celcius | Temperature @ 2m |
| dewPointTemp.2 | deg.celcius | Dew point temperature @ 2m |
| rh.2 | % | Relative humidity @ 2m |
| psfc | pa | Surface pressure |
| msl | pa | Mean sea-level pressure |
| sst | deg.celcius | Sea surface temperature |
| blh | m | Boundary layer height |
| tcc | % | Total cloud cover |
| fsr | m | Forecast surface roughness |
| tclw | kg/m2 | Total column liquid water |
| tciw | kg/m2 | Total column ice water |
| charnock | ~ | Charnock |
| heatFlux | w/m2 | Instantaneous surface sensible heat flux |
| lowCc | % | Low cloud cover |
| medCc | % | Medium cloud cover |
| hiCc | % | High cloud cover |
| eastTss | N m**-2 | Instantaneous eastward turbulent surface stress |
| northTss | N m**-2 | Instantaneous northward turbulent surface stress |
| zust | m/s | Friction velocity |
| cbh | m | Cloud base height |
| uvbAcc | w/m2 | Downward UV radiation at the surface |
| sshfAcc | w/m2 | Surface sensible heat flux |
| ssrdAcc | w/m2 | Surface solar radiation downwards |
| ssrAcc | w/m2 | Surface net solar radiation |
| ssrcAcc | w/m2 | Surface net solar radiation, clear sky |
| tisrAcc | w/m2 | TOA incident solar radiation |
| fdirAcc | w/m2 | Total sky direct solar radiation at surface |
| cdirAcc | w/m2 | Clear-sky direct solar radiation at surface |
| ssrdcAcc | w/m2 | Surface solar radiation downward clear-sky |
Attribution
If data from this dataset is used within any private or public disseminations, then EMD and its data providers must be acknowledged.
Source: ERA5 (Native Grid). Distribution through EMD and windPRO - EMD International A/S, 2020. This dataset uses ERA5 which is being developed through the Copernicus Climate Change Service (C3S). Data processing and distribution for ERA5 is carried out by ECMWF.
External Links
- ECMWF - What is ERA5 - https://software.ecmwf.int/wiki/display/CKB/What+is+ERA5
- ERA5 Data Documentation at ECMWF - https://software.ecmwf.int/wiki/display/CKB/ERA5+data+documentation
- Copernicus Climate Change Service - ERA5 Page - https://climate.copernicus.eu/products/climate-reanalysis