A preliminary survey of large-scale disturbances over the tropical Pacific región

Abstract

A preliminary study is made of some dynamical characteristics of large-scale disturbances appeared in the Marshall Islands area during June and July of 1958. The average period of the waves in the lower tropospheric easterlies is about four days and that of the high-Ievel migratory vortices is about six days. The vertical distributions of vorlicity and vertical motion associated with the distubances are estimated directly from the upper wind observations. Existence of large-scale vertical motion with the disturbance and its controlling effect of the upper air temperature and the shower activity are discussed. An attempt is also made to distinguish the developing and non developing disturbances at their early stage. An indication of warming of the middle trophosheric air together with weak absolute vorticity aloft is shown to be an almost necessary and sufficient condition for the development of a wave disturbance into a typhoon.