Comparison of atmospheric profiles between COSMIC radio occultation and radiosonde observations in the Qinghai-Tibetan Plateau

A comparison of atmospheric profiles between COSMIC radio occultation and radiosonde observations is performed to explore their discrepancies in the Qinghai-Tibet Plateau (QTP). The results show as follows. (1) The atmospheric profiles of COSMIC have a satisfactory correlation to those of radiosondes. Compared to radiosondes, the COSMIC temperature, pressure and water vapor pressure have a bias of -0.2 ℃, 1.7 hPa and 0 hPa, respectively, with a corresponding root-mean-square error (RMSE) of 1.8 ℃, 1.6 hPa and 0.4 hPa. The discrepancies are larger in lower than upper troposphere and decrease with altitude. (2) The precipitable water (PW) calculated from the wet atmospheric profiles of COSMIC also has a reasonable correlation to that of radiosondes. However, the COSMIC PW is smaller than that of radiosondes, with a bias of -5.0 mm and a RMSE of 5.7 mm. The discrepancy between them is obvious in lower troposphere. (3) The instability of radiosonde sounding in near surface layer and the limited ability of model used in the COSMIC retrieval method in the QTP are mainly responsible for the discrepancy of atmospheric profile in lower troposphere, and the underestimated COSMIC PW is due to the underestimated COSMIC refractivity.