Winter winds can also take sand storms with them from drier areas, isentropic Potential Vorticity Analysis and cold air activity during the period of excessively heavy rain over Changjiang-Huaihe River Basin in 1991 而冷风同时也会来到干燥地区生成沙尘暴,1991年江淮特大暴雨的位涡分析与冷空气活动