Ma. Filiberti et al., 4-DIMENSIONAL VARIATIONAL ASSIMILATION OF SSM I PRECIPITABLE WATER-CONTENT DATA/, Quarterly Journal of the Royal Meteorological Society, 124(549), 1998, pp. 1743-1770
Satellite microwave radiometers provide measurements of precipitable w
ater content (PWC) over the oceans, with a horizontal resolution of a
few tens of kilometres. These data represent the water vapour content
integrated over the atmospheric column. We assess the value of this so
urce of information for numerical weather prediction systems. We used
the European Centre for Medium-Range Weather Forecasts Integrated Fore
casting System with a four-dimensional variational method to assimilat
e the Special Sensor Microwave/Imager (SSM/I) PWC data over a 24-hour
period. Our experiments use an incremental variational method. Compari
son with observations is made using a multi-level global primitive-equ
ation T106 spectral model with physical parametrizations. Minimization
is performed using a T63 adiabatic dynamics model which includes only
simplified physics (horizontal diffusion, a simple surface drag and a
vertical diffusion scheme). Comparing the control and assimilation ex
periments with aircraft and other data shows that the use of PWC data
from SSM/I improves the analysis. We also obtain a slight improvement
in short-range forecasts of almost all parameters when SSM/I-PWC data
are used in the assimilation.