南半球冬季双西风急流及数值模拟

Double-Westerly Jet in the Austral Winter and Its Numerical Simulation

基于NCEP/NCAR再分析资料研究了南半球冬季双西风急流现象,指出它发生在600～100hPa的南太平洋上空,其中副热带急流中心位于27.5°S,且在200hPa层风速达到极大值;高纬度急流中心位于60°S,风速随高度增加而增加。在此基础上,利用IAP 9L AGCM(大气物理研究所9层大气环流模式)对双西风急流现象进行了数值模拟。结果表明,该模式很好地再现了双西风急流现象,并成功地模拟出副热带急流的位置、强度以及最大风速的垂直中心层次。对极区急流强度的模拟也比较接近实况,但位置偏南。但模式对40～50°S之间南太平洋风速极小值中心强度的模拟略低于再分析资料。此外,模式对平流层上层单急流位置的模拟与观测结果有较大差异。

The double westerly jet（DWJ） in the austral winter is studied by using the NCEP/NCAR reanalysis data. Results show that the DWJ splits into two branches over the South Pacific from 600 hPa to 100 hPa,with the subtropical branch at 27.5°S and the polar counterpart at 60°S. The maximal speed value level of the former is at 200 hPa while the speed of the latter tends to increase with height with the maximum speed at above 100 hPa. Based on the observation, a nine-level atmospheric general circulation model developed in Institute of Atmospheric Physics （IAP 9L AGCM） is employed to simulate the DWJ. In general, the model is successful in simulating the position, strength and vertical structure of the subtropical westerly jet and the simulated polar westerly jet below 200 hPa is also realistic. On the other hand, the model fails to simulate the single westerly jet in the lower stratosphere.