台风“麦莎”的强度对台风前部飑线发展过程影响的研究

对2005年8月5日16时(UTC,下同)至6日00时发生的一次台风前部飑线过程进行了数值模拟,分析表明:台前飑线在母体台风和副高之间的湿区生成。台风为这次台前飑线过程提供了有利的条件,包括强的低空急流输送充沛的水汽,强的不稳定环境产生大的对流有效位能以及强的地表辐合,使得初始的离散的对流单体组织发展形成台前飑线。成熟时期的台前飑线虽然比中纬度和热带飑线的变压强度小,但是具有更强的低层暖湿空气入流,中层的入流范围也更加宽广。敏感性试验结果表明:台风强度越强,其台前飑线的回波强度越强,移动速度更快,生命史也更长。强台风使得低空垂直风切变更大,有利于台前飑线的生成和发展,在台前飑线发展成熟后,低空垂直风切变强度减小,不利于台前飑线的维持,加之低空水汽输送的减少,使其逐渐趋向衰亡。

Impact of Typhoon Intensity on the Development of a Pre-Tropical Cyclone Squall Line

A severe pre-TC (Tropical Cyclone) squall line that preceded Typhoon Matsa (2005) was investigated using the non-hydrostatic "Weather Research and Forecast" model. The results showed that this pre-TC squall line formed in the moist transition zone between the parent TC and a subtropical high. It was found that Matsa may have contributed to convective development in the squall line by producing conditional instability and enhancing low-level moisture convergence, leading to the organization of the early discrete convection into a linear rainband. Although the pre-TC squall line caused fewer surface pressure perturbations at its mature stage than is typically observed at mid-latitudes, it exhibited stronger moisture convergence in the boundary layer and a larger area of inflow in the mid-troposphere. Sensitivity analyses showed that stronger TCs give pre-TC squall lines that are longer lived and faster moving, with more intense rainfall. The results showed that a stronger TC tends to produce more low-level vertical wind shear in the transition zone, which favors the organization of early discrete convection into a squall line. However, low level vertical wind shear in the vicinity of the pre-TC squall line decreases when the mature stage is entered. This, in addition to the likelihood of a reduced low-level moisture supply, appears to be one of the factors that is unfavorable for the pre-TC squall line being maintained.