Assimilation of GNSS Radio Occultation Profiles into GCM Fields for Global Climate Analysis

This paper investigates the application of the 3D-Var methodology within a global climate monitoring framework. It studies the assimilation of GNSS radio occultation derived refractivity profiles into ECMWF analysis or short-term forecast fields as background. The system is tuned for high vertical and moderate horizontal resolution, best suited to the spatial characteristics of these satellite based measurements. The analyses are performed on a GCM-compliant Gaussian grid, comprising 60 model levels up to a height of ∼60 km and a horizontal resolution corresponding to a triangular spectral truncation T42 (i.e., T42L60). Within the system two different operational modes are implemented, the first updating a refractivity background, derived from ECMWF analysis fields, the second directly updating the ECMWF temperature, specific humidity and surface pressure fields. First results indicate a significant analysis increment, emphasising the ability of RO data to add independent information to ECMWF analysis fields.