10:45 〜 12:15
[AAS03-P07] Numerical Simulation of Severe Precipitation in the Taipei Basin on June 4, 2021
キーワード：Meiyu front, local circulation, cold pool, severe precipitation
On June 4, 2021, the area in Taiwan was affected by the Meiyu front and the outer circulation of the mild typhoon CHOI-WAN. A strong convective system appeared in Taipei City during the afternoon and was accompanied by heavy rainfall. The hourly rainfall was as high as 209 mm, setting a record for the highest hourly rainfall in Taipei City in the past 20 years. In this study, the WRF model was applied to simulate the three-layer nested grid (the highest spatial resolution was 500 m). The results showed that the thermal and dynamic mechanisms of the ambient atmosphere and the establishment of local circulation had a significant impact on the rainfall intensity and extent of the Taipei Basin. In addition, simulations and observations showed that the typhoon's outer circulation brought southwest airflow with abundant moisture, and the southwest wind strengthened the convergence with the northward wind from the frontal system near the northern seas of Taiwan, unstable conditions to the environmental field were built.
The urban heat island effects over the Taipei Basin make the near-surface convection more unstable, thereby increasing the chance of deep convection development. Tamsui River Valleys and Keelung River Valleys which are located in the northwest and northeast of the Taipei Basin transported the moisture by sea breeze to the Taipei Basin. The graduated moisture air is easily lifted by the terrain to produce convective rainfall even when it is transmitted to the mountainous area in the southeast of the basin. Besides, the sea breeze collided with the outflow of the cold pool caused by the precipitation at the bottom of the mountain, and then the strong moisture flux generated on the boundary of the lower layer converged, and the upwelling of the lower layer jointly induced severe precipitation; Later, due to the outflow of cold air, the sea breeze entered the basin turns from the northerly wind to the southerly wind, which further spread the severe precipitation to the Taipei Basin, and caused the heavy rainfall.
The urban heat island effects over the Taipei Basin make the near-surface convection more unstable, thereby increasing the chance of deep convection development. Tamsui River Valleys and Keelung River Valleys which are located in the northwest and northeast of the Taipei Basin transported the moisture by sea breeze to the Taipei Basin. The graduated moisture air is easily lifted by the terrain to produce convective rainfall even when it is transmitted to the mountainous area in the southeast of the basin. Besides, the sea breeze collided with the outflow of the cold pool caused by the precipitation at the bottom of the mountain, and then the strong moisture flux generated on the boundary of the lower layer converged, and the upwelling of the lower layer jointly induced severe precipitation; Later, due to the outflow of cold air, the sea breeze entered the basin turns from the northerly wind to the southerly wind, which further spread the severe precipitation to the Taipei Basin, and caused the heavy rainfall.