中国地区CMEM观测算子微波亮温模拟

Microwave Brightness Temperature Simulated by CMEM Observation Operator in China

针对数值气象预报及陆面模拟分析系统中的同化模块,本文以ERA-Interim再分析资料中的地表状态变量数据为依据,采用社区微波发射模型(community microwave emission model,CMEM)为观测算子,模拟水平和垂直极化方向的大气层顶亮温,并采用高级微波扫描辐射计-地球观测系统(advanced microwave scanning radiometer-earth observing system,AMSR-E)亮温观测,对模拟结果进行验证和精度评定,分析亮温模拟与亮温观测存在偏差的原因。研究结果表明,CMEM模拟垂直极化方向的微波亮温比水平极化模拟效果好,更接近AMSR-E观测数据;CMEM模拟的微波亮温在中国西北和西南地区的模拟效果较好,模拟与观测的相关系数达0.8左右,而中国南方地区亮温模拟效果较差,说明CMEM观测算子对裸地或者植被稀疏的地区模拟效果好,对有植被覆盖密集的地区亮温模拟效果较差。该研究为CMEM在中国地区的应用提供了理论依据。

The assimilation module is a core part in the numerical meteorological forecasting and analysis system of the land surface simulation.In this paper,we use surface state variable from ERA-Interim reanalysis data and CMEM(Community Microwave Emission Model)observation operator to simulate horizontal and vertical polarizations of brightness temperature at top of the atmosphere.Then the simulation result and accuracy are verified and analyzed by the AMSR-E(Advanced Microwave Scanning Radiometer for EOS Aqua)observations.The result shows that vertically polarized simulation is closer to AMSR-E observation and better than horizontally polarized simulation.CMEM has a superior simulation performance in northwestern and southwestern regions of China as the correlation coefficients between the simulation and AMSR-E observations are larger than 0.8.By contrast,CMEM has a poor performance in southern areas of China.These results illustrate that CMEM observation operator has better simulation effect in bare or sparse vegetation area than in dense vegetation area.Our results reveal that special attention should be paid to the vegetated areas in China when assimilating or simulating brightness temperature at the top of the atmosphere.Moreover,we recommend to use vertically polarized brightness temperature in direct assimilation system with the aim to improve the accuracy of soil moisture in the topmost of soil layer.This study provides a theoretical basis for the application of CMEM in China.