Title: A modeling study of the severe afternoon thunderstorm event at Taipei on 14 June 2015: The roles of sea breeze, microphysics, and terrain
Lecturer: Prof. Mingren Yang ( National Taiwan University )
Date: Thursday, April 18, 2019 at 14:00 PM
Venue： Lecture Hall D103, School of Atmospheric Sciences
Abstract： On 14 June 2015, a severe afternoon thunderstorm event associated with cell merger developed within the Taipei basin, which produced intense rainfall (with rainfall rate of 131 mm/h) and urban-scale flooding. Cloud-resolving WRF simulations were performed to capture reasonably well the onset of see breeze, the development and evolution of convective cells, and several cell mergers within the afternoon thunderstorm system. The WRF model had four nested grids (with the finest grid size of 0.5 km) in the horizontal and 55 layers in the vertical to explicitly resolve the deep convective cells inside the thunderstorm. It is found that convection was initiated by sea breeze at foothill and by upslope wind from the valley at mountain peak, respectively. Convective available potential energy (CAPE) was increased by 800 to 3200 J/kg with abundant moisture transport by the sea breeze from 08 to 12 LST, fueling large thermodynamic instability for the development of afternoon thunderstorm. The strong convergence between sea breeze and cold-air outflow triggered further development of intense convection, resulting in heavy rainfall over Taipei city. Microphysics sensitivity experiments show that evaporative cooling played a major role in the propagation and intensification of cold-air cold outflow, while melting cooling played a minor role. The terrain-removal experiment indicates that the local topography of Mount Datun may produce the channel effect through Danshui River Valley, intensify sea-breeze circulation and transport more moisture, increase CAPE and result in stronger thunderstorm with heavier rainfall.