ERA5 Gaussian Grid

Winds @ 100m

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:

1. Newer modelling system
2. More observations used in the assimilation
3. Higher spatial horizontal resolution (around 31 km compared to 79 km)
4. 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.

Resolution, Coverage and Evaluation

Correlation improvement, ERA5-MERRA2

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:

1. EMD-WRF On-Demand Validation Report and
2. EMD-WRF Europe+ Validation Report

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.

Table: Overview of the windPRO subset of ERA5 parameters.

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.