GFDL_RegCM对21世纪西北太平洋热带气旋活动的情景预估

首先评估了GFDL模式对西北太平洋热带气旋(TC)环境热力及动力因子的模拟性能,再利用夏威夷大学国际太平洋研究中心高分辨率区域气候模式( IPRC-RegCM),进行降尺度研究西北太平洋TC活动特征,在此基础上预估21世纪全球变暖背景下(A1B)西北太平洋TC活动的主要特点.结果显示,在西北太平洋TC活动区,GFDL控制试验的海平面温度(SST)比ERSST偏低.与NCEP/NCAR再分析资料相比,GFDL模拟的1980-1999年大尺度环流平均场表现为:副高脊线平均位置近乎一致,西伸脊点偏东,强度偏弱,面积偏小；季风槽槽线的范围偏小,强度偏弱；水平风垂直切变值在南海及菲律宾群岛海域偏小,而在160°E～170°W的20°N以南偏强.与NCEP/NCAR强迫的模拟结果相比,GFDL强迫得到的TC源地频数在南海偏少,菲律宾群岛以东海域偏多,两者的季节及年际变化特征相似.路径频数在南海北部和我国华南沿岸显著偏多.AlB情景下,西北太平洋TC生成数目将增加一倍,生成源地偏北且同时向东部洋而扩展,路径频数增多主要发生在20°N以北的中东部洋面上,移经西北太平洋西部的TC频数减少,由此影响我国的TC将减少.TC频数的季节分布发生较大变化,最多的月份在10月.TC平均强度增强,最大强度在10月增加最多,这与10月SST的增加和环境风切变的减小均为最大值有密切的关系.

SCENARIOS OF 21ST CENTURY TROPICAL CYCLONE ACTIVITY OVER WESTERN NORTH PACIFIC AS PROJECTED BY GFDL_REGCM

Large-scale environmental conditions simulated by GFDL_CM2_1 (GFDL) were evaluated. The conditions are associated with the western North Pacific (WNP) tropical cyclones (TC) activity. TC activity and its scenarios for the 21st century over WNP were studied in downscaling from the output of GFDL_CM2_1 in 20C3M and A1B simulation by University of Hawaii International Pacific Research Center high-resolution regional climate model. Results showed that the sea surface temperature (SST) is lower than that of NOAA over eastern regions of active TC, and the subtropical high and monsoon trough are weak with the former moving to the east. The wind shear is small over South China Sea (SCS) and near the Philippines, while it intensifies south of 20 °N between 160 °E and 170°W. Seasonal and interannual changes of TC genesis frequency forced by 20C3M are in agreement with those by U.S. National Centers for Envioronmentl Prediction/National Center for Atmospheric Research (NCEP/NCAR). However, these changes decrease over SCS and increase in the Philippine Sea. The simulated occurrence is much more than the result forced by NCEP/NCAR for northern SCS and the South China coast. In the A1B scenario, the total number of TC in WNP will increase by about 100% and the genesis positions will move northward and eastward. As a result, the increase of TC occurrence will be mainly in eastern WNP and north of 20 °N. Less TC will pass through western WNP so that the TC frequency that influences China will decrease. However, the average intensity will increase. There is a large seasonal change in TC activity with the maximum of both frequency and intensity occurring in October, which is closely associated with the maximal increase of SST and the decrease of vertical wind shear in that month.