Proceedings - C-SRNWP Project

3) Averaged emissivities + dynamically adjusted skin temperature from one channel for each
instrument
We show below results from the dynamical approach (1). Figure 4 shows the comparison of
innovation values for a number of AMSU-A microwave channels, using the standard or the
new surface emissivity maps. It is clear that the innovations have been reduced drastically for
assimilation experiments using the new maps, most notably for low-level sensitive channels.
Very little impact is seen for the mid- and high level channels. Identical results have been
obtained for AMSU-B and SSM/I channels over land. The reduced innovations (and biases)
allow to start assimilating additional low-level channels for impact studies. This work is
ongoing. First results indicate a significant impact on the distribution of humidity and
precipitations, especially in the Tropical areas for Arpège tests. Further tests also in the LAM
model are expected.
Figure 4: statistics of innovations for 6 AMSU-A channels, using the standard surface
emissivity conditions (black) or the new maps (blue).
3.2. Tests of 3D-VAR assimilation over North Africa
The Moroccan Aladin team has undertaken an extensive testing of the 3D-VAR assimilation
over a wide North-African domain. Yet, the absence of major components of the satellite
radiance data for the time being prevents an operational usage of 3D-VAR. progressively, the
installation of satellite data databases, conversions and monitoring will allow a testing of the
complete observation assimilation system. Figure 5 shows biases of 2m temperatures for both
the dynamical adaptation (Arpège-triggered spin-up model) and the 3D-VAR assimilation
systems over North-Africa. Despite the fairly small amount of observational information (a
number of surface stations, aircraft data and a few radiosondes), the assimilation system
already competes reasonably well with the spin-up model.
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