| dc.description.abstract | Taiwan is located in Southeast of Asia, prevailing southwest monsoon wind, and developing sea breeze usually affect local weather during daytime. Both factors interact with terrain providing a favorable condition to develop afternoon convection. However, due to lack of intensive observation stations and long-term data, related studies on the afternoon convection and local circulation are limited. In this study, WRF and observation data of TASSE were used to simulate and analyze the key factors resulted in the development of the afternoon convection occurred on July 1, 2017.
According to the composite reflectivity images on July 1, 2017, convective system began to develop in the windward of the Central Mountain Range and Snow Mountain Range, and gradually moved and spread northward. It brought rainfall to the north of Taiwan, and the maximum hourly accumulated rainfall exceeded 100 mm, caused flooding in many roads of towns. This paper found that under the influence of weak synoptic environment, the south component of wind brought warm moist air to Taiwan, provided the conditions of the atmospheric instability. The analysis of TASSE observation data showed that the height of the development of the sea breeze was higher,
also had obvious convectively unstable layer. After comparing observations with simulation results showed that convective systems organized at 13 LST in the mountains. Meanwhile, the model result showed that topographic affected surrounding flow and interacted with the development of the sea breeze, there is obvious
convergence wind flow in Taipei basin and northern mountain. We can see the wind field on the windward interacts with terrain and cause uplifting through the cross section analysis of the convective system position. From the analysis of this case, the key factors responsible for the generation of the system is the development of sea breeze and topographic effects.
Based on the sensitivity tests of terrain and surface heat flux, we found that the environmental flow can directly affect the onshore wind field when there is no
terrain blocking, and make the position of convective system closer to the coast. Meanwhile, because of the lack of the terrain, the precipitation intensity is much smaller. After the surface heat flux being removed, the thermal circulation is weakened. Thus, the sea and land breeze is difficult to develop, most of the convective system is resulted from the interaction between the environmental wind field and the terrain, leading to
the rain area only concentrated in the windward side of the mountain. Through the sensitivity test of the model, we could understand the importance of these two factors
for afternoon heat convection. | en_US |