TRMM海表降水率同化在热带气旋Danas(2001)数值模拟中的应用研究

Four-dimensional variational data assimilation of TRMM data in numerical prediction of TC Danas(2001)

研究了TRMM/TMI海表降水率资料的四维变分同化在热带气旋(TC)数值模拟中的作用.使用中尺度气象模式MM5设计了若干数值试验模拟了TC Danas(2001)由热带低压初生到台风生成的发展过程.在满足MM5模式动力约束的前提下,将TRMM海表降水率资料直接同化进入较高分辨率(18 km)的模式初始场.结果表明,使用MM5模式的4D-VAR同化系统直接同化TRMM/TMI海表降水率资料是可行的.这种做法提高了TRMM资料的利用率,不仅在模式初始场中加入了更多实测信息,而且避免了两次同化(1DVAR+4DVAR)可能引起的误差.直接同化TRMM资料通过调整气压、温度、湿度等要素初始场,改善了模式对热带气旋结构(如暖心、涡度、散度)的描述和降水的模拟.在此基础上,同化不仅改进了对Danas强度的模拟,而且成功地模拟了热带气旋环境场的演变过程,因而改进了路径的模拟.

The impact of TRMM/TMI surface rainfall rate （SRR） 4DVAR on numerical simulation ot TC Danas （2001） is studied. Several numerical experiments are performed with mesoscale model MM5 to investigate the development of Danas from TC genesis to a typhoon. Under the dynamic constraint of MM5 model , the SRR data are assimilated directly in the initial meteorological field （18 kin）. The direct assimilation of SRR data with MM5 4DVAR is proved to be feasible, which not only incorporate as many observation data available as possible but also avoid the resultant error due to the twice cycles of assimilation （1DVAR＋4DVAR）. On the basis of adjusting the initial fields （SLP, temperature, humidity and so on）, the direct assimilation of TRMM SRR improves the description of TC structure （such as warm-core, vorticity and divergence） and the prediction of rainfall. As a result, the intensity and track of Danas are simulated successfully with TRMM SRR assimilation.