View source for ERA5 Gaussian Grid

[[Category:Online Data]][[Category:Wind Data]][[File:ERA5_WindsAt100m.png|thumb|right|300px|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:

# 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 -  [http://help.emd.dk/mediawiki/images/8/81/20170829_ERA5_WindPRO_ReleaseNote.pdf see here].

'''ERA5 and EMD-WRF Mesoscale Services'''<br>
EMD has incorporated the ERA5 data in to its EMD-WRF on-demand setup and its pre-run datasets - read more [https://www.emd.dk/windpro/mesoscale-data/ here]. A thorough validation of ERA5 in a EMD-WRF modelling context has been conducted and included in two technical notes covering [http://help.emd.dk/knowledgebase/content/TechNotes/TechnicalNote6_EMD-WRF_On-Demand_20180116.pdf EMD-WRF On-Demand] services and [http://help.emd.dk/knowledgebase/content/TechNotes/TechnicalNote7_EMDWRF_EUROPE_Validation.pdf EMD-WRF Europe+] pre-run mesoscale dataset.

'''ERA5T - Available in the "ERA5(T) Rectangular Grid" dataset'''<br>
During early december 2019, ECMWF released the ERA5T dataset. ERA5T is preliminary ERA5 data, but updated with a shorter 5 calender day delay. The ERA5T, is currently unavailable for the native, reduced gaussian grid. This is due to technical limitations at ECMWF and at the Copernicus Climate Data Store. In windPRO, a supplementary [[ERA5(T)_Rectangular_Grid|ERA5(T) Rectangular Grid]] dataset is created to provide the most recent and up-to-date ERA5 data - read more at our ERA5/5T wiki-page [http://help.emd.dk/mediawiki/index.php?title=ERA5/5T_(Rectangular_Grid) here].

== Dataset Description: Resolution, Coverage, Period and Update Schedule ==
* '''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. <br>
* '''Coverage:''' Coverage is global for land-areas and coastal regions. In windPRO, offshore coverage is covers a distance of approximately 300 km from any known coastline. <br>
* '''Period:''' The EMD databases holds data from 1988 until present day. <br>
* '''Update Schedule''': Monthly - from December 2017 ECMWF started monthly updates of ERA5 so that onward data from a new month is added every month with a 2-3 month delay. 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 [https://climate.copernicus.eu/products/climate-reanalysis here]. Preliminary data (ERA5T) is currently not available for the native/Gaussian grid data - if you need data that is near real-time - then please use the [[ERA5_(Geographic_Grid)|ERA5 (Geographical Grid)]] data instead.

== Validations ==
[[File:CorrelationGraph.png|right|300px|thumb|Correlation improvement, ERA5-MERRA2]]'''First ERA5 Data Evaluation:'''<br>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,  [http://help.emd.dk/mediawiki/images/8/81/20170829_ERA5_WindPRO_ReleaseNote.pdf here].<br>

'''Additional Data Evaluations:'''<br>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: 
# [http://help.emd.dk/knowledgebase/content/TechNotes/TechnicalNote6_EMD-WRF_On-Demand_20180116.pdf EMD-WRF On-Demand Validation Report] and 
# [http://help.emd.dk/knowledgebase/content/TechNotes/TechnicalNote7_EMDWRF_EUROPE_Validation.pdf EMD-WRF Europe+ Validation Report]

== Known Issues and Usage Notes ==
* '''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 - see error report : [https://confluence.ecmwf.int/pages/viewpage.action?pageId=127305868 here].
**'''Solution:''' ERA5 data in windPRO are not influenced by this problem: We are (currently, ultimo 2018) procuring data directly from ECMWF (and not the CDS) - and also distributing physical heights of 10m and 100m.<br>
*'''2020-01-08:'''
**'''Issue:''' ECMWF has released the ERA5T data (preliminary data) as a part of its Copernicus Climate Data Store (CDS) offerings, see [https://confluence.ecmwf.int/display/CUSF/Release+of+ERA5T here]. These data are preliminary, can be used to extend the ERA5 data - and are available on a daily basis with a 5-day delay from real time. The ERA5T data are currently available only on a 0.25 degree rectangular lat-lon grid, so not directly compatible with the native model (Gaussian) gridded data.
**'''Solution:''' If you need the ERA5T data - it is now (January 2020) - also possible to download ERA5 and ERA5T data in windPRO on the geographical grid. EMD will update/ammend this dataset - ERA5 (Gaussian Grid) - when the ERA5T data become available at the native grid resolution. EMD is in dialog with ECMWF towards this issue, and representatives from ECMWF have confirmed that the ERA5 data will be available for the gaussian grids also.

== 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.

<center>
{| class="wikitable"
|+ align="bottom"|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
|}
</center>

== Required Modules/Licenses ==
To access the ERA5 reanalysis data from within windPRO - the following licenses/modules are required in your windPRO setup:
* Basis
* METEO
When the license fee is paid, you then have access to the full dataset without further cost. Downloading of data is unrestricted for licenced users with an active service subscription, however, a "fair use" policy applies. Visit [http://www.emd.dk/windpro/online-ordering/ EMD online ordering] to purchase the needed licences.

== Attribution ==
If data from this dataset is used within any private or public disseminations, then EMD and its data providers must be acknowledged. 
<pre>
Source: 
ERA5 (Gaussian 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.
</pre>

== External Links ==

* ECMWF - What is ERA5 - [https://software.ecmwf.int/wiki/display/CKB/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 https://software.ecmwf.int/wiki/display/CKB/ERA5+data+documentation]
* Copernicus Climate Change Service - ERA5 Page - [https://climate.copernicus.eu/products/climate-reanalysis https://climate.copernicus.eu/products/climate-reanalysis]