The electron densities from EISCAT observations show obviously the wellknown winter anomaly in solar maximum and a semiannual variation in solar minimum.

The northerly component of the winter monsoon anomaly makes the anomalous cyclone over the western Pacific not exist and the East Asian summer monsoon becomes stronger.

The interannual cycle of SOTA in the tropical Pacific is driven by zonal wind anomaly over the equator ial western Pacific which is caused mainly by anomalous East-Asian winter monsoon.