7B.4 A Quality Control Based on the Local Spectral Width of COSMIC Radio Occultation for Data Assimilation

Liu, Hui, Y.-H. Kuo, S. Sokolovskiy, S.-P. Ho, Z. Zeng, L.-F. Hsiao, and B.C. Ruston, University Corporation for Atmospheric Research/Constellation Observing System for Meteorology, Ionosphere, and Climate

In this study, we first examine potential bias of COSMIC radio occultation (RO) refractivity with respect to radiosonde and ECMWF analysis in the situation of strong non-spherical symmetric fluctuations in the lower tropical troposphere. The local spectral width (LSW) of wave-optics transformed RO signals is derived to characterize the uncertainty of RO due to the fluctuations. We examine COSMIC refractivity from the period of 2008-2014 and find that COSMIC refractivity has large negative biases (up to -6%) in the situation of high LSW with respect to both radiosonde observations and global ECMWF analysis. The COSMIC refractivity having the high LSW and large biases accounts about 20% of total RO data. We show that a standard quality control based on the departure of RO data from a model background is less effective in eliminating the biases. We propose a quality control which disregards the COSMIC refractivity having the high LSW to eliminate the large biases. Preliminary assimilation experiments with the Weather Research and Forecasting (WRF) model show that this LSW-based quality control reduces noticeably a dry bias in the WRF analysis and forecast in the lower tropical troposphere.