Experiments with assimilation of ZTD GPS data

Abstract

Preliminary assimilation experiments have been performed at INM to find the impact of GPS Zenith Total Delay data with the HIRLAM 3DVar system. The two alternative background constraint formulations available in HIRLAM, namely analytical and statistical, have been tested. They have been done with emphasis in the diagnostic of the performance of the assimilation cycle using this new type of observations, as in the verification of the model forecasts. These experiments have shown an impact of the assimilation of GPS data and the background constraint approach, both on precipitation and model humidity .