9421060 Chen In this project, the synoptic-scale, mesoscale and local processes favorable for the development of heavy precipitation during TAMEX will be studied based on the results form numerical models and the data collected during the Taiwan Area Mesoscale Experiment (TAMEX). As the Mei-Yu front approached the island of Taiwan, the prefrontal southwest monsoon flow (or the low-level jet) brought in the warm, moist unstable air from the south. In addition to the low-level lifting (orographic and frontal), the presence of upper-level forcings (the upper-level divergence related to diffluent airflow or the frontogenetical forcing associated with a jet-front system) is required for the development of widespread rainstorms in the subtropics. In this study, we will diagnose a LLJ based on the model generated high resolution data. In particular, the link between the cyclongenesis and the development of LLJ will be further investigated. In addition, we will study the coupling between the upper-level and low-level circulations leading to the development of widespread precipitation. The synoptic-scale circulations regulate whether or not widespread precipitation will occur, whereas mesoscale circulations, local circulations and orographic effects govern the details of precisely when and where the convection will occur. We will study the prefrontal mesoscale airflow over the Taiwan area based on radar, aircraft and conventional data as well as a nested grid model. In particular, we will focus on the airflow on the windward side as the upper-level trough/low-level jet approached. In the prefrontal southwesterly flow, the deflected southerly jet along the coast and results in a localized convergence zone favorable for the development of deep convection. As the front moved over the northern Taiwan, the deflected southerly flow may merge with the undeflected southwesterly flow in the Taiwan Strait off the northwestern coast and results in a localized convergence zone favorable for the development of deep convection. As the front moved over the northern Taiwan, the deflected southerly flow may converge with the postfrontal northeasterlies and results in an enhanced frontal convergence zone along the coast. To assess the effects of thermally driven circulations caused by the diurnal heating cycle on precipitation, we will study the rainfall characteristics during the diurnal cycle at different parts of the island. In addition, we will conduct a case study of local circulations over the island under the prefrontal southwest monsoon flow based on the data collected during IOP #11.
