On the 30-50 day Tropospheric Oscillation During the 1978-79 Northern Winter

Abstract

Tropospheric oscillation in the period range of 30-50 days during the 1978/79 winter season was studied using statistical and synoptic approaches. The analysis confirms earlier investigations that this low frequency mode is a broad frequency band phenomenon which involves primarily the zonal wind oscillation. It is very prominent over the Tropical belt of the Indian and Pacific Ocean, in particular, over the convective zones of the winter monsoon. The oscillation differs from its counterpart of the Indian summer monsoon, notably in the absence of divergent meridional propagation over the ascending regions of the winter monsoon circulation. However, prominent poleward phase propagations were observed over the eastern Pacific Ocean; this propagating mode seems to form over the near equatorial region, but is strongly barotropic away from the Equator. It appears that the synoptic scale motions over the Tronical Pacific Ocean are modulated by this low freauencv mode.