Atmospheric Chemistry and Physics, vol. 13, issue 22 (2013) pp. 11209-11219
There has been growing interest in the vertical structure of the recent
Arctic warming. We investigated temperatures at the surface, 925, 700,
500 and 300 hPa levels in the Arctic (north of 70 degrees N) using
observations and four reanalyses: ERA-Interim, CFSR, MERRA and NCEP II.
For the period 1979-2011, the layers at 500 hPa and below show a warming
trend in all seasons in all the chosen reanalyses and observations.
Restricting the analysis to the 1998-2011 period, however, all the
reanalyses show a cooling trend in the Arctic-mean 500 hPa temperature
in autumn, and this also applies to both observations and the reanalyses
when restricting the analysis to the locations with available IGRA
radiosoundings. During this period, the surface observations mainly
representing land areas surrounding the Arctic Ocean reveal no
summertime trend, in contrast with the reanalyses whether restricted to
the locations of the available surface observations or not.
In evaluating the reanalyses with observations, we find that the
reanalyses agree better with each other at the available IGRA sounding
locations than for the Arctic average, perhaps because the sounding
observations were assimilated into reanalyses. Conversely, using the
reanalysis data only from locations matching available surface (air)
temperature observations does not improve the agreement between the
reanalyses. At 925 hPa, CFSR deviates from the other three reanalyses,
especially in summer after 2000, and it also deviates more from the IGRA
radiosoundings than the other reanalyses do. The CFSR error in summer
T-925 is due mainly to underestimations in the Canadian-Atlantic sector
between 120 degrees W and 0 degrees. The other reanalyses also have
negative biases in this longitude band.
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