利用常规观测资料、NCEP/NCAR的1°×1°再分析资料和WRF3.2模式的模拟结果分析了一次由台风"海鸥"与西风槽远距离相互作用产生的山东暴雨过程的水汽和干冷空气活动。结果表明:水汽辐合主要来自南边界的水汽流入,南边界水汽输入的增强主要是台风向北的水汽输送造成的,对流层低层的低涡使水汽在山东中西部地区集中。南北方向水汽辐合的大小与降水量有较好的对应关系。暴雨过程中有明显干冷空气活动,暴雨初期,对流层顶的干冷空气先行侵入降水区,引起高层西风加速和辐散加强,进而导致上升运动发展。暴雨发展期,对流层中层(500 hPa或600 hPa)干冷空气由西北向东南以偏西气流的方式侵入降水区,与暖湿空气以东西风的形式辐合上升。暴雨强盛期,对流层中层不仅有来自中纬度西北方向的干冷空气侵入,而且还有来自高纬的干冷空气侵入。干侵入始终具有高层超前于低层的特点,有利于位势不稳定的发展。干冷空气与暖湿空气活动的加强使山东地区中低层锋生加强,激发非地转垂直上升运动,是上升运动加强的机制之一。暴雨过程中对流性不稳定和条件性不稳定共存,干冷空气侵入使等相当位温面倾斜及强迫暖湿气流沿锋面倾斜上升,有利于条件性对称不稳定的发展。
A heavy rainfall event that occurred in Shandong Province on 17-19 July 2008 was caused by the interaction between typhoon Haiou and westerly trough. The water vapor and the activities of dry and cold air of this heavy rainfall event were studied by using routine observation, NCEP/NCAR 1°×1° reanalysis and simulated data from the WRF3.2 model. The results show that the water vapor convergence was mainly from the inflow of the southern boundary. The intensification of the inflow of the water vapor from southern boundary primarily contributed to the northward transportation of water vapor from the typhoon. The convergence of water vapor in the west and middle parts of Shandong Province resulted from the vortex in the lower troposphere. The convergence of water vapor in the south-north direction corresponded well with rainfall. Dry and cold air apparently intruded into rainfall area in the process of the rainfall. In the initial phase of the heavy rainfall, dry and cold air in the tropopause first intruded into the rainfall area and induced the acceleration of west wind in the high levels and the enhancement of divergence, which led to the development of upward motion. In the development phase of the heavy rainfall, dry and cold air in the middle troposphere (500 hPa or 600 hPa) intruded into rainfall area with westerly wind from northwest to southeast and met with warm and moist air, resulted in upward motion. In the heavy rainfall period, dry and cold air came not only from northwest in the mid-latitude but also from the high latitudes. Dry intrusion in the higher levels was always ahead of that in the lower levels, which is favorable to the development of potential instability. The activities of dry and cold air as well as warm and moist air intensified frontogenesis in the lower and middle levels in Shandong Province and ageostrophic ascending motion was triggered, which is one of the mechanisms of the intensification of the ascending motion. Convective instability and conditional symmetric instability existed in the heavy rainfall event. Dry intrusion can slant the equivalent potential temperature surface and force warm and moist air to move upward slantwise along front, which is beneficial to the development of conditional symmetric instability.
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