1. CNR-IMAA,Tito Scalo,Italy
2. Ecole Polytechnique,IPSL, CNRS,Palaiseau Cedex,France
3. Federal Office of Meteorology and Climatology,MeteoSwiss,Payerne,Switzerland
4. University of Cologne, Institute for Geophysics and Meteorology,Cologne,Germany
5. European Space Agency,ESTEC,Noordwijk,The Netherlands