COSMIC掩星资料反演青藏高原大气廓线与探空观测的对比分析

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

利用青藏高原地区COSMIC掩星资料反演的大气湿廓线Wet Prf数据和8个站点的探空数据,分析了COSMIC反演大气廓线和可降水量与探空观测的偏差,并考查了偏差随高度的变化特征。结果显示:(1)COSMIC反演的温度、压强和水汽压廓线与探空观测具有很好的正相关;与探空观测相比,COSMIC的温度、压强和水汽压的偏差为-0.2℃、1.7 h Pa和0 h Pa,均方差为1.8℃、1.6 h Pa和0.4 h Pa;COSMIC反演大气廓线与探空观测的偏差基本上在大气低层较大,然后随高度增加而减小。(2)COSMIC反演的可降水量与探空观测正相关较好;COSMIC反演的可降水量低于探空观测,两者的偏差为-5.0 mm,均方差为5.7 mm;两者的负偏差在大气低层最明显。(3)探空观测在近地层的不稳定性和COSMIC反演方法中背景模式在青藏高原地区描述大气状态的能力有限,是造成COSMIC反演大气廓线和探空观测的偏差在近地层较大的主要原因;COSMIC观测的折射率偏小导致其反演的可降水量偏低。

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 h Pa and 0 h Pa, respectively, with a corresponding root-mean-square error（RMSE） of 1.8 ℃, 1.6 h Pa and 0.4 h Pa. 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.