| dc.description.abstract | Heavy rainfall events during early summer rainy season over Taiwan is an important issue because it usually causes severe disasters. During 17-20 May 2019, the synoptic wearher patterns are favorable for convections developing and a mei-yu front which is stranded in the southern part of the East China Sea moves south and passes through Taiwan. There are three heavy rainfall events with daily accumulative rainfall exceeding 200 mm, which occurred in northwestern Taiwan on 17 May, central mountainous area on 18 May and northern Taiwan on 20 May respectively. This study focuses on the formation and development mechanisms of these three heavy rainfall events and the interaction between low-level jets (LLJs) and convection systems. In addition, the role of terrain effects will also be discussed in this study.
On 17 May, the barrier jet over northwestern Taiwan converges with the westerly wind in front of the mei-yu front over northern Taiwan Strait, as a result, the mesoscale convective system (MCS) develops over the ocean. With the synoptic system-related low-level jet (SLLJ) exists around 700 hPa, the MCS extends to the northwestern area of Taiwan, causing the heavy rainfall event over Taoyuan and Hsinchu coast areas. On 18 May, the prevailing wind combining with upslop wind is lifted by central mountains range (CMR), resulting in heavy rainfall over the mountainous area during daytime. On 20 May, as the front moves closely to Taiwan, the barrier jet converges with the northwesterly wind and convections are present over Taipei and causing considerable precipitation.
Several sensitivity experiments of terrain effect are performed. With the model terrain removed (NT run) and increased (1.5H run), the rainfall distribution and the amount of the accumulated rainfall are evidently distinct. On 17 and 20 May, the barrier jet over northwestern area of Taiwan is disappeared in NT run and stronger in 1.5H run. On 18 May, the orographic lifting effect by CMR is disappeared in NT run and the orographic blocking effect of CMR is obvious in 1.5H run. The accumulative rainfall on 17 May is weaker in NT run and slightly shifts northernly in 1.5H run; it decreases and shifts to eastern Taiwan in NT run and shifts to western coast in 1.5H run on 18 May; rainfall over northern Taiwan is not present in NT run and decreases in 1.5H run on 20 May.
In summary, the barrier jet plays an important role for heavy rainfall events over northern Taiwan on 17 and 20 May cases and the SLLJ influences the movement of the MCS on 17 May case. 18 May case shows the localized diunal circulation is important for the precipitation over mountainous area. During 17-20 May, a boundary layer jet (BLJ) along South China coast over South China Sea is present, playing an important role on moisture transport. In addition, as the upstream wind for Taiwan, the intensity of the barrier jet might depend on it. Consequently, it can be researched in future probably. | en_US |