On the depiction of upper-level precursors of the 1999 December storms from TOVS observations
Fourrié, N. ; Claud, C. ; Chédin, A.
Année de publication
2003
At the end of December 1999, two extremely severe storms only one day
apart affected western Europe and caused considerable damage. A variable
derived from satellite observations, the so-called temperature of the
lower stratosphere (TLS), is used in this study for detecting and
tracking the upper-level components of these storms. TLS is computed
from a regression over five Television and Infrared Observation
Satellite (TIROS-N) Operational Vertical Sounder (TOVS, aboard NOAA
satellites) channels, with coefficients calculated from a climatological
dataset [thermodynamical initial-guess retrieval (TIGR)], and provides
information on the temperature near the tropopause. The objective of
this paper is to assess the ability of TLS, in situations such as these
two exceptional storms, to track and depict upper-tropospheric
precursors of surface lows. After a brief synoptic description of the
meteorological situation, TLS fields as well as the Action de Recherche
Petite Échelle Grand Échelle (ARPEGE) model fields (mean sea level
pressure, temperature, wind velocity, and geopotential height of the
dynamical tropopause) are discussed concurrently for the period 2327
December. Although the upper-level thermal fields are consistent
overall, differences appear, especially during the incipient stage of
the second storm. The forecast, which was poor in the operational
context, is modified when a configuration close to the TLS one is
adopted. Qualitative comparisons of TLS with Microwave Sounding Unit
(MSU) channel-3 limb-corrected brightness temperatures and with the
water vapor imagery are also shown. One advantage of TLS over these two
other fields is the earlier detection of the upper-level precursor of
the second storm. Because TLS computation is easy and fast, the
suitability of TLS as a possible forecasting aid over midoceanic regions
is promoted.</div>
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