ERA5 Gaussian Grid
Introduction
ERA5 is a climate reanalysis dataset developed through the Copernicus Climate Change Service (C3S) and processed/delivered by ECMWF. The dataset is intended to replace the ERA-Interim dataset from ECMWF shortly after the ERA5 dataset is complete. 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 comparison to ERA-Interim and MERRA2 is also included in this note. here.
Resolution, Coverage and Evaluation
Resolution:
The 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 an area of approximately 300 km from the coastline.
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.
Release Plan
The release of the remaining parts of ERA5 is following the schedule from C3S and ECMWF (see the image to the right). The first batch of data covers the period of 2010-2016. It was released during summer 2017. In December 2017 ECMWF started monthly updates of ERA5 so that a new month is added every month with a 2-3 month delay. The data from 1979-2009 is planned to completed end 2018. The period dating back to 1950 will be available in 2019. 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 |
ERA5 and EMD-WRF Mesoscale Services
EMD has incorporated the ERA5 data in to its EMD-WRF on-demand setup. Read more here: <here>. A thorough validation of ERA5 in EMD-WRF has been conducted and included in this technical note: <EMD-WRF On-Demand>.
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
Acknowledgements and Credits
- ERA5 is being developed through the Copernicus Climate Change Service (C3S).
- Data processing and distribution for ERA5 is carried out by ECMWF.