Gianpaolo Balsamo
Météo France
The study concerns the analysis of soil moisture for the operational
mesoscale model of Meteo-France ALADIN. A simplified variational
technique (2D-Var) has been implemented to analyse soil moisture by
assimilating screen-level observations of temperature and relative
humidity. The linearized versions of the observation operator are
obtained through finite differences from extra integrations of the
numerical model with perturbed initial soil moisture states. Two
fundamental assumptions of the methods (linearity of the observation
operator and horizontal decoupling between grid points) are evaluated.
The validation of the method is done with real observations using
different time windows: a sequential assimilation cycle of 6-h allows a
comparison with the operational optimal interpolation technique, while a
24-h window is considered to extend the temporal consistency of the
assimilated observations in the analysis. Results from the 2D-Var
analyses show realistic soil moisture retrievals when compared to an
independent soil moisture estimation produced by an hydrological
off-line system. The benefits of the 2D-Var analysis are also shown by
an improvement of the forecast of screen-level variables.