Synoptic Study of a Medium-Scale Oceanic Cyclone during AMTEX '75

Abstract

A severe extratropical cyclcone was initiated from a low-level medium-scale cyclone over the ocean northeast of Taiwan during the initial phase of the AMTEX '75. The analyses of Soliz and Fein were used to examine the time evolution and the three-dimensional structure of the medium-scale cyclone associated with this AMTEX cyclone. During the initial period of this system's development there was no evidence that forcing by an approaching synoptic-scale system was involved. The distribution of zonal wind did not suggest the existence of barotropically or baroclinically unstable conditions in the lower troposphere. The analysis shows that several processes were important in the initiation and development of this system. Heat flux from the Kuroshio current rapidly destabilized the lower layer of the polar air mass. Mild lifting due to warm advection led to latent heat release and the formation of the 850 mb short wave and surface pressure trough. Further release of latent heat within the region of the low-level disturbance resulted in the development of the medium-scale cyclone. The vertical coupling of the cyclone and the incoming upper-level synoptic system led to the development of the severe extratropical cyclone.