Further Studies of a Prefrontal Convective Rainband During TAMEX IOP 13: Part I:Reflectivity History and Cell Evolution

Abstract

Radar measurements obtained from both conventional and Doppler radars were used to study the life cycle of a prefrontal convective rainband during TAMEX IOP 13 on 25 June 1987. The conventional radar data were available at 20-min intervals, while Doppler data were available at 7-min intervals. Additionally, surface observations at 30-min intervals taken from nine stations over the west coast and the Taiwan Strait were also used for analysis to determine the approximate positions of the Mei-Yu front and the leading edge of the rainband (gust front).

Results show that a prefrontal convective rain band formed in the vicinity of the Mei-Yu front when the system was located far north of the island. As the rainband moved slowly down the central west coast, it began to move away from the front as gust fronts were formed by cells at the leading edge of the system.

The convective cells generated low-level cold outflows in the warm sector to the southeast of the front. Part of these cold outflows moved toward the southeast, interacting with the strong moisture-rich southwest monsoon flow to form a gust front. At the same time, the southwestern portion of the front, located 50-60 km west of the coast, continued to lift moist air, generating a new cell along the front. This new cell then traveled to the east at a more rapid speed following the prevailing westerly flow at low levels. It eventually merged with the main (old) cell, thereby prolonging the lifetime of the rainband. The analysis in this study, as a whole, further supports the conceptual model of this rainband reported in the study by Lin et al. (1992) using two volumes of dual-Doppler data obtained from CP-4 and TOGA (Tropical Ocean and Global Atmosphere).

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