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| Titel |
Using MODIS land surface temperatures and the Crocus snow model to understand the warm bias of ERA-Interim reanalyses at the surface in Antarctica |
| VerfasserIn |
H. Fréville, E. Brun, G. Picard, N. Tatarinova, L. Arnaud, C. Lanconelli, C. Reijmer, M. van den Broeke |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 8, no. 4 ; Nr. 8, no. 4 (2014-07-31), S.1361-1373 |
| Datensatznummer |
250116253
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| Publikation (Nr.) |
 copernicus.org/tc-8-1361-2014.pdf |
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| Zusammenfassung |
| Moderate-Resolution Imaging spectroradiometer (MODIS) land surface
temperatures in Antarctica were processed in order to produce a gridded data
set at 25 km resolution, spanning the period 2000–2011 at an hourly
time step. The Aqua and Terra orbits and MODIS swath width, combined with
frequent clear-sky conditions, lead to very high availability of
quality-controlled observations: on average, hourly data are available
14 h per day at the grid points around the South Pole and more than 9 h over a
large area of the Antarctic Plateau. Processed MODIS land surface
temperatures, referred to hereinafter as MODIS Ts values, were compared with in
situ hourly measurements of surface temperature collected over the
entirety of the year 2009 by seven stations from the Baseline Surface Radiation Network (BSRN)
and automatic weather stations (AWSs). In spite of an occasional failure in
the detection of clouds, MODIS Ts values exhibit a good performance, with a
bias ranging from −1.8 to 0.1 °C and errors ranging from 2.2 to 4.8 °C root
mean square at the five stations located on the plateau. These results show that
MODIS Ts values can be used as a precise and accurate reference to test other
surface temperature data sets. Here, we evaluate the performance of surface
temperature in the European Centre for Medium-Range Weather Forecasts (ECMWF)
reanalysis known as ERA-Interim reanalysis. During conditions detected as
cloud free by MODIS, ERA-Interim shows a widespread warm bias in Antarctica
in every season, ranging from +3 to +6 °C on the plateau. This confirms a
recent study which showed that the largest discrepancies in 2 m air
temperature between ERA-Interim and the global temperature data set HadCRUT4
compiled by the Met Office Hadley Centre and the University of East Anglia's
Climatic Research Unit occur in Antarctica. A comparison with in situ surface
temperature shows that this bias is not strictly limited to clear-sky
conditions. A detailed comparison with stand-alone simulations by the Crocus
snowpack model, forced by ERA-Interim, and with the ERA-Interim/land
simulations, shows that the warm bias may be due primarily to an
overestimation of the surface turbulent fluxes in very stable conditions.
Numerical experiments with Crocus show that a small change in the
parameterization of the effects of stability on the surface exchange
coefficients can significantly impact the snow surface temperature. The
ERA-Interim warm bias appears to be likely due to an overestimation of the
surface exchange coefficients under very stable conditions. |
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