应用一维变分法反演GPS掩星大气温湿廓线

GPS掩星观测的折射率是大气温度、湿度状态的函数, 应用一维变分方法 (1DVAR) 可以从折射率资料中同时反演出大气温、湿度廓线, 利用COSMIC 2011年中国区域掩星观测数据对这一方法进行了测试, 背景场采用ECMWF大气廓线, 反演结果与相匹配的探空观测有较好一致性. 重点研究了一维变分反演方法中非理想气体效应 (non-ideal effect) 对温度、湿度反演误差的影响, 不同月份的比较结果表明, 非理想气体效应对掩星反演大气廓线是一种系统性影响, 考虑这一效应可对温度反演改进0.1 K的偏差 (bias), 对比湿可改进约0.5%偏差. 掩星资料作为数值天气预报资料同化中少数无需偏差改正的卫星遥感资料, 非理想气体效应改正是无疑是非常重要的, 此外, 考虑这一效应对掩星资料的气候应用也有重要价值. 关键词： 一维变分 掩星 非理想气体效应

1DVAR retrieval method for GPS radio occultation measurements of atmospheric temperature and humidity profiles

GPS radio occultation observed refractivity is a function of atmospheric temperature and humidity. One-dimensional variational (1DVAR) analysis can be used to retrieve temperature and humidity profiles simultaneously from refractivity data. Profiles derived from 1DVAR method with COSMIC 2011 data occurred in China area are compared with the collocated radiosondes. The background data are ECMWF profiles and the retrieval results show good agreement with radiosondes. The effect of non-ideal gas compressibility on temperature and humidity retrieval errors is focused on in the 1DVAR analysis. Results compared with different months data show that non-ideal gas compressibility has a systematic effect on radio occultation retrieved atmospheric profiles. Including non-ideal gas effect correction the temperature bias to radiosondes is around 0.1 K, while the specific humidity bias is 0.5%. Because radio occultation data can be assimilated into operational numerical weather prediction system without bias correction, taking into consideration non-ideal gas effect is clearly very important. In addition, including this effect in radio occultation retrieval has important impact on climate applications.
Keywords： one-dimensional variation GPS occultation non-ideal gas effect