台风暴雨过程中位势散度波作用密度分析和预报应用研究

The analysis of the potential-divergence wave activity density and its application to typhoon precipitation

在位涡的基础上,考虑散度效应,把水平风矢量旋转90°后的旋度在广义位温梯度方向上的投影定义为位势散度,并把其二阶扰动量定义为位势散度波作用密度,该波作用密度代表扰动热量的扰动输送,与位势稳定度的发展演变有关.登陆台风Morakot(2009)的诊断分析表明,在台风登陆台湾岛,进入台湾海峡和登陆大陆三个阶段,波作用密度高值区与大陆和台湾降水区相重叠,扰动热量的扰动输送显著;在前两个阶段,大陆和台湾降水区波作用密度逐渐增大,扰动热量的扰动输送逐步增强;在台风登陆福建霞浦市后,大陆地区波作用密度减小,扰动热量的扰动输送减弱.在影响波作用密度局地变化的诸多物理因素中,扰动非地转风位涡项是主要强迫项.统计分析表明,波作用密度与观测降水有一定的相关性,据此发展了位势散度波作用密度降水预报方程,其本质是数值模式预报资料的动力延伸释用,预报应用表明,利用24h模式预报场计算的波作用密度降水能够较好地再现观测降水的落区,对台风Morakot引发的暴雨有一定的预报技巧.

Based on the potential vorticity, combining the divergence wind vector spinned 90 degrees on the general potential temperature potential divergence, and its second order disturbance quantity was potentla advection potential effect, the projection of the gradient was defined as the the wave activity density of divergence. The wave activity density of potential divergence represents the disturbance transportation of the disturbance heating, which is related with the evolution of stability. The analysis of the landfall typhoon ＂Morakot＂ shows that the high value ofthe wave activity density overlapped the precipitation region during the three stages of the location on Taiwan, Taiwan Strait, and the mainland of typhoon ＂Morakot＂. In the first two stages, the wave activity density and the disturbance transportation of the disturbance heating in rain region enhanced, while after the landfall, they decreased. In all physical effect on the local variation of the wave activity density, the potential vorticity of disturbance ageostrophic wind was the main forcing term. Long-term statistics shows that the wave activity density and the observation precipitation have close relationship, so the potential divergence wave activity density torrential rain forecast equation was deduced, which is the dynamical extension of the numerical model prediction data. The prediction application of it shows that the wave activity density precipitation calculated by the 24hr-model prediction field matched well with the observation, which was favourable to the rainfall prediction caused by Morakot.