Comparison of large-scale dynamical variability in the extratropical stratosphere among the JRA-55 family data sets: impacts of assimilation of observational data in JRA-55 reanalysis data
This study compares large-scale dynamical variability in the extratropical stratosphere, such as major stratospheric sudden warmings (MSSWs), among the Japanese 55-year Reanalysis (JRA-55) family data sets. The JRA-55 family consists of three products: a standard product (STDD) of the JRA-55 rea...
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-09-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/17/11193/2017/acp-17-11193-2017.pdf |
Summary: | This study compares large-scale dynamical variability in
the extratropical stratosphere, such as major stratospheric sudden warmings
(MSSWs), among the Japanese 55-year Reanalysis (JRA-55) family data sets.
The JRA-55 family consists of three products: a standard product (STDD) of
the JRA-55 reanalysis data and two sub-products of JRA-55C (CONV) and
JRA-55AMIP (AMIP). CONV assimilates only conventional surface and upper-air
observations without assimilation of satellite observations, whereas
AMIP runs the same numerical weather prediction model without assimilation
of observational data. A comparison of the occurrence of MSSWs in Northern
Hemisphere (NH) winter shows that, compared to STDD, CONV delays several MSSWs by 1 to
4 days and also misses a few MSSWs. CONV also misses the Southern Hemisphere
(SH) MSSW in September 2002. AMIP shows significantly fewer MSSWs in Northern Hemisphere winter and
especially lacks MSSWs of the high aspect ratio of the polar vortex in which the
vortex is highly stretched or split. A further examination of daily
geopotential height differences between STDD and CONV reveals occasional
peaks in both hemispheres that are separated from MSSWs. The delayed and
missed MSSW cases have smaller height differences in magnitude than such
peaks. The height differences for those MSSWs include large contributions
from the zonal component, which reflects underestimations in the weakening of
the zonal mean polar night jet in CONV. We also explore strong planetary
wave forcings and associated polar vortex weakenings for STDD and AMIP. We
find a lower frequency of strong wave forcings and weaker vortex responses
to such wave forcings in AMIP, consistent with the lower MSSW frequency. |
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ISSN: | 1680-7316 1680-7324 |