ATOVS辐射率资料的直接变分同化试验研究

THE EXPERIMENTS ON DIRECT ASSIMILATING ATOVS RADIANCE

文中采用增量三维变分 ( 3D Var)同化方法 ,对先进的微波探测装置 (AMSU A)探测的辐射亮温资料与常规探空资料在MM5中尺度数值预报模式中的直接同化和预报进行对比试验研究。结果表明 ,同化AMSU A辐射亮温资料对中高层温度分析场的影响最明显 ,对MM5模式的温度和水汽混合比预报有总体上的正效应 。

Two comparison experiments, i.e.NOAMSUA and AMSUA, were performed for simulating a very heavy rainstorm occurring in Wuhan City and the region to its east in 21-22 July 1998. In Exp. NOAMSUA, radiosonde observations were assimilated while in Exp. AMSUA radiosonde observations and brightness temperatures of NOAA-15 AMSU-A channels 4-14 were assimilated simultaneously. Then the assimilation analyses of the both comparison experiments were taken respectively as initial conditions of numerical prediction model for simulating that process. In this paper, an incremental three-dimensional variational (3D-Var)method was used as data assimilation method. The MM5 mesoscale model (version 3) acted as assimilation model and prediction model as well. The analysis increments of Exp. AMSUA were compared with that of Exp. NOAMSUA, so did the forecast results. The comparisons in terms of the analysis increments showed that direct assimilating the AMSU-A brightness temperatures adjusted the temperature background of the mid and upper troposphere more distinctly. The result is attributed to the temperature information of the mid and upper layers in Exp. AMSUA being enriched by the addition of the AMSU-A channels 4-14 measurements, which could only detect temperature above 700 hPa except channel 4 detecting surface atmospheric temperature. The simulation results showed that the forecasts of temperature and mixing ratio of water vapor were generally better in Exp. AMSUA than in Exp. NOAMSUA. It was also found that in each experiment, the simulation of the major influencing weather systems in the heavy rainstorm process, the low-level southwest vortex and the cold shear was preferable, and the predicted areas and grades of heavy rains somewhat fitted to the real time rainfalls. But all the precipitation forecasts of Exp. AMSUA seem not superior to that of Exp. NOAMSUA, which may also result from few information on humidity being contained in the AMSU-A measurements.