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 rainband 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 anew 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).
Highlights
In the studies by Lin et al ( 1 992) and Lin et al ( 1 993), the structure of a subtrop ical prefrontal rainband in the Taiwan Area Mesoscale Experiment (TAMEX) IOP 1 3 \\'as investigated in detail using dual-Doppler data at 0653 and 0700 LST, 25 June 1 987
Organized convection was initiated and maintained by the frontal lifting of a 10\:\1-level jet (LLJ) in the boundary layer, and the main moisture supply came from the high-Be monsoon air at low levels
The data used in this study included the surface observations at 30-min intervals from 0200 to 2400 LST 25 June as well as radar observations obtained from the Kaohsiung (744) conventional radar, and the TOGA (770) Doppler radar
Summary
In the studies by Lin et al ( 1 992) and Lin et al ( 1 993), the structure of a subtrop ical prefrontal rainband in the Taiwan Area Mesoscale Experiment (TAMEX) IOP 1 3 \\'as investigated in detail using dual-Doppler data at 0653 and 0700 LST (local standard time), 25 June 1 987. It moved slowly along the central west coast toward the south-southeast at 2.5 m/s The maintenance of this long-lived rainband was caused by the factors of 1) frontal lifting; 2) a gust front arising from the convective downdraft ahead of the front; and 3) discrete developments in advance ot' the line. The reflectivity history of the rainband revealed by both the Kaohsiung and TOGA radars were used to demonstrate line motion, precipitation pattern, cell merger and other related features Such structural features make it possible for researchers to further understand the formation and maintenance of this long-lasting, heavy-rain-producing convective rainband during the TAMEX IOP 1 3
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