A Study on the Severe Precipitation Induced by the Meiyu Front in Taiwan

Along the coast of northwestern Taiwan, when the Meiyu front passed, there were occasional rapids caused by the terrain, and after convergence with the prevailing wind field, it caused severe precipitation. In 1987, some studies conducted by Taiwan mesoscale experiment (TAMEX) found that low-level jet (about 1 km high) under certain conditions, known as barrier jet, strongly affected the heavy rainfall in northern Taiwan. On the morning of June 2, according to the results of the study in the Meiyu frontal contact north Taiwan, in just 12 hours later to Keelung and north coast down to the super heavy rain of reason, may be related to frontal subject in northern Taiwan snowy mountains, the enhancement of barrier jets occurring near the surface height is related to the increase in barrier jets during the movement of the frontal body. The results of this study show that when the Meiyu front moves southeast, the enhancement of the convective system on the front may cause by a larger inclination angle with its front, with appropriate movement speed, through the southwest airflow in front of the Meiyu front, especially a barrier of about 1 km in height. The warm and humid air introduced by the jet is related. Strong convection will develop in a forced convergence zone off the northwestern part of Taiwan, and the convergence zone is mainly caused by a combination of sub-synoptic forcing such as low-level wind shear convergence, barrier jets, and convective feedback of non-adiabatic terms. In addition, due to the existence of the barrier jet and the frontal wind shear zone, cyclonic circulation around the jet area was generated. With the instability of the temperature gradient and the enhancement of the abnormal zone of the positive potential vorticity, it is speculated that it should be the cause of the severe precipitation in this case. Because the biggest difference between the first and the second strong precipitation may come from the complicated topographic effect and limited space, this research focuses on the reasons for the development of the first severe weather development and heavy precipitation.