Major changes have been introduced in the description of the
soil-atmosphere-vegetation interactions in the global NWP model
ARPEGE. An updated version of the so-called ISBA scheme, with a
parametrization of soil water freezing, is now used to
describe exchanges over land surface. Besides, a new soil
moisture analysis has been introduced, based on the 2m temperature and
relative humidity forecast errors through an optimal interpolation scheme.
All these modifications have become operational on 1998/03/16, simultaneously
in the global variable resolution NWP model (ARPEGE-25km over France)
and in the Limited Area Model (ALADIN).
Two experiments -with and without the parametrization soil water freezing-
of one-year long assimilation (upper air and soil moisture),
covering 1997, have been performed with a lower model resolution
(T79, without streching).
The impact of the soil water freezing will be presented.
The annual cycle of soil temperature and soil moisture are
preserved and no drift has been noticed.
These experiments have also been used to produce a first approximation
of the climatological fields (soil moisture and soil temperature)
required by the operational model.