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The Japan Meteorological Agency (JMA) conducted JRA-55, the second
Japanese global atmospheric reanalysis project. It covers 55 years,
extending back to 1958, coinciding with the establishment of the
global radiosonde observing system. Compared to its predecessor,
JRA-25, JRA-55 is based on a new data assimilation and prediction
system (DA) that improves many deficiencies found in the first
Japanese reanalysis. These improvements have come about by
implementing higher spatial resolution (TL319L60), a new radiation
scheme, four-dimensional variational data assimilation (4D-Var) with
Variational Bias Correction (VarBC) for satellite radiances, and
introduction of greenhouse gases with time varying concentrations.
The entire JRA-55 production was completed in 2013, and thereafter
will be continued on a real time basis.
Specific early results of quality assessment of JRA-55 indicate that
a large temperature bias in the lower stratosphere has been
significantly reduced compared to JRA-25 through a combination of
the new radiation scheme and application of VarBC (which also
reduces unrealistic temperature variations). In addition, a dry land
surface anomaly in the Amazon basin has been mitigated, and overall
forecast scores are much improved over JRA-25.
Most of the observational data employed in JRA-55 are those used in
JRA-25. Additionally, newly reprocessed METEOSAT and GMS data were
supplied by EUMETSAT and MSC/JMA respectively. Snow depth data over
the United States, Russia and Mongolia were supplied by UCAR, RIHMI
and IMH respectively.
The Data Support Section (DSS) at NCAR has processed the 1.25 degree
version of JRA-55 with the RDA (Research Data Archive) archiving and
metadata system. The model resolution data has also been acquired,
archived and processed as well, including transformation of the
TL319L60 grid to a regular latitude-longitude Gaussian grid (320
latitudes by 640 longitudes, nominally 0.5625 degree). All RDA
JRA-55 data is available for internet download, including complete
subsetting and data format conversion services.