Recent developments on the assimilation of GNSS-RO bending angles in the Météo-France 4D-Var system
Presenter:
Dominique Raspaud
Météo-France/CNRS, DR/CNRM
Météo-France/CNRS, DR/CNRM
Talk
The GNSS-RO bending angles have been operationally assimilated in the Météo-France global model ARPEGE since 2007, firstly with the FORMOSAT-3/COSMIC constellation, CHAMP and GRACE. They are currently assimilated up to 50 km and the tangent point drift is taken into account.
The presentation will focus on recent developments regarding the use of observations and the observation operator.
With the recent availability of new GNSS-RO receivers on FY-3 and Metop-C polar orbiting satellites, a significant amount of observations has been added to the ARPEGE four-dimensional variational (4D-Var) data assimilation system. This increase represents up to 50 % additional GNSS-RO data with a positive impact in terms of objective forecast skill scores.
A version of the two-dimensional bending angle observation operator developed at ECMWF (Healy et al., 2007) has been adapted to the tilted and stretched grid of the global model ARPEGE in order to take into account horizontal gradients of refractivity. The first results of comparisons with the one-dimensional observation operator will be given in terms of background error statistics and forecast scores.
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