The activity of cold air and interannual variation of low level jet are important cause of interannual variation of the rainfall in april . interannual variation of subtropic high is the main cause of interannual variation of the rainfall in may over north china . there is significant negative correlation between interdecadal variation of the rainfall in april and that of sst in the areas of equatorial indian ocean and tropic middle - east pacifi 华北4月降水与热带中东太平洋、赤道印度洋海温年代际变化呈明显的负相关:华北5月降水与热带中东太平洋、赤道印度洋海温年代际变化存在明显的正相关:热带海温的年代际异常引起的副热带高压的年代际异常可能是影响华北4 、 5月降水异常的重要原因。
