The Impact of Vertical Resolution in the Assimilation of GPS Radio Occultation Data

Abstract The sensitivity of GPS radio occultation (GPSRO) bending angle assimilation to vertical resolution was studied within a global three-dimensional variational data assimilation (3DVAR) system. The sensitivity experiments were performed using different vertical resolutions of GPSRO data at 2 km, 1 km, 500 m, and 200 m. The assimilation of the higher vertical resolution GPSRO data showed better consistency in the analysis–forecast cycle in terms of the differences between GPSRO bending angle data and 6-h forecasts (O-F). This resulted in an improved analysis of the temperature, geopotential height, and wind in the mid-/upper-level troposphere by the hydrostatic response and the related model dynamics. It should be noted that the highest vertical resolution of the GPSRO data (200 m in this study) improved the forecasting skill level in terms of the root-mean-square error (against the European Centre for Medium-Range Weather Forecasts analysis) and the anomaly correlation of the geopotential height forecasting at 500 and 200 hPa in both the Northern and Southern Hemispheres. The benefits of assimilating higher vertical resolution GPSRO data were more pronounced in the upper-level troposphere, which was in agreement with previous studies using real GPSRO observations.