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Malardel, S., N. Wedi, W. Deconinck, M. Diamantakis, C. Kuhnlein, G.
Mozdzynski, M. Hamrud, and P. Smolarkiewicz, 2015: A new grid for
the IFS. Newsletter No. 146 - Winter 2015/16, ECMWF, 6 pp., URL:
https://www.ecmwf.int/sites/default/files/elibrary/2016/15041-newsletter-no-146-winter-201516.pdf.
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After many years of research and technical preparation, the
production of a new ECMWF climate reanalysis to replace ERA-Interim
is in progress. ERA5 is the fifth generation of ECMWF atmospheric
reanalyses of the global climate, which started with the FGGE
reanalyses produced in the 1980s, followed by ERA-15, ERA-40 and
most recently ERA-Interim. ERA5 will cover the period January 1950
to near real time, though the first segment of data to be released
will span the period 2010-2016.
ERA5 is produced using high-resolution forecasts (HRES) at 31
kilometer resolution (one fourth the spatial resolution of the
operational model) and a 62 kilometer resolution ten member 4D-Var
ensemble of data assimilation (EDA) in CY41r2 of ECMWF's Integrated
Forecast System (IFS) with 137 hybrid sigma-pressure (model) levels
in the vertical, up to a top level of 0.01 hPa. Atmospheric data on
these levels are interpolated to 37 pressure levels (the same levels
as in ERA-Interim). Surface or single level data are also available,
containing 2D parameters such as precipitation, 2 meter temperature,
top of atmosphere radiation and vertical integrals over the entire
atmosphere. The IFS is coupled to a soil model, the parameters of
which are also designated as surface parameters, and an ocean wave
model. Generally, the data is available at an hourly frequency and
consists of analyses and short (18 hour) forecasts, initialized
twice daily from analyses at 06 and 18 UTC. Most analyses parameters
are also available from the forecasts. There are a number of
forecast parameters, e.g. mean rates and accumulations, that are not
available from the analyses. Together, the hourly analysis and twice
daily forecast parameters form the basis of the monthly means (and
monthly diurnal means) found in this dataset.
Improvements to ERA5, compared to ERA-Interim, include use of
HadISST.2, reprocessed ECMWF climate data records (CDR), and
implementation of RTTOV11 radiative transfer. Variational bias
corrections have not only been applied to satellite radiances, but
also ozone retrievals, aircraft observations, surface pressure, and
radiosonde profiles.
NCAR's Data Support Section (DSS) is performing and supplying a grid
transformed version of ERA5, in which variables originally
represented as spectral coefficients or archived on a reduced
Gaussian grid are transformed to a regular 1280 longitude by 640
latitude N320 Gaussian grid. In addition, DSS is also computing
horizontal winds (u-component, v-component) from spectral vorticity
and divergence where these are available. Finally, the data is
reprocessed into single parameter time series.
Please note: As of November 2017, DSS is also producing a CF 1.6
compliant netCDF-4/HDF5 version of ERA5 for CISL RDA at NCAR. The
netCDF-4/HDF5 version is the de facto RDA ERA5 online data format.
The GRIB1 data format is only available via NCAR's High Performance
Storage System (HPSS). We encourage users to evaluate the
netCDF-4/HDF5 version for their work, and to use the currently
existing GRIB1 files as a reference and basis of comparison. To ease
this transition, there is a one-to-one correspondence between the
netCDF-4/HDF5 and GRIB1 files, with as much GRIB1 metadata as
possible incorporated into the attributes of the netCDF-4/HDF5
counterpart.
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