Experiments of GPS slant path data assimilation with an advanced MM5 4DVAR system

Abstract

In a previous study the authors developed and optimized tools for 4 -dimensional variational assimilation ( 4 DVAR) of Global Positioning System (GPS) ground-based Slant Total Delay (STD) data in the framework of the Mesoscale Model 5 (MM5) system. In this study, advantage is taken from the parallel implementation of 4DVAR and the availability of STD data processed at the Helmholtz Centre Potsdam, German Research Centre for Geosciences (GFZ), providing data for a large and continuously operating network of groundbased receivers in Germany. The results of two long-term assimilation experiments are presented. The first assimilation experiment, performed over a period of two weeks (1-14 August 2007), shows that the impact in STD observation space of an independent network of GPS receivers is positive. After the assimilation window the impact is decreasing with time, lasting in average for 12 h. The second assimilation experiment, performed over a period of one month (1-31 August 2007), indicates that the impact on the precipitation forecast is weak but positive.