华北强飑线生成环境与地形作用的数值试验研究

A Numereical Experiment of Topographic Effect on Genesis of the Squall Line in North China

应用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（ 简称ＬＡＳＧ）η坐标有限区域数值预报模式，简称为ＬＡＳＧ－ ＲＥＭ，对１９８３ 年６ 月２７ 日一次华北强飑线生成与地形作用进行了数值试验研究。首先运行的对照试验，获得了以往分析得到的有关飑线的现象。模拟１ 小时后，飑线发生前，对流层高层有较强的冷平流侵入华北地区。３ 小时后，在燕山及其南侧背风坡地区，对流层中、低层出现明显的锋生现象，这对飑线的生成和发展起了重要的作用。模拟至６ 小时，近地面层在日变化增温的时段内，开始出现降温现象，这时实况的飑线开始形成，这降温现象是与飑线后方的中尺度湿绝热下沉运动有关。８ 小时后，对流层高层在继续维持西北气流冷平流的条件下，由降温转变为明显升温，并产生一个α中尺度的温度脊，这是由飑线上强的深对流过程引起的热量向上输送造成的。这也是飑线发生发展后，中尺度系统对大尺度背景场的反馈的结果。紧接着近地面层出现最强的降温。这与中尺度湿绝热下沉运动的发展和小尺度的下击暴流有关。这一过程与过去分析结果相一致。其次，在对照试验成功的基础上，对地形作了敏感性试验，试验结果表明：在西北流型条件下，高层有较强的冷空气侵入。

The numerical experiment of topographic effect on genesis of squall line on 27 June 1983 in North China is investigated by the LASG η coordinate limited-area mesoscale model (LASG-REM). First, the model is run for the control experiment, which captured main observed features of the squall line as we analyzed previously. After one hour, there is a stronger cold advection in the upper troposphere in North China prior to the genesis of a squall line. Three hours later, there is an frontogenesis area in the lower troposphere (700 hPa) over the Yanshan Mountain and its southern lee area, which plays an important role for the genesis of the squall line. Run to the sixth hour, the temperature starts decrease on the surface, when the daily variation of surface temperature is increasing. It is assocaited with the mesoscale condensation adiabatic subsidence behind the squall line. After eight hours, the temperature starts increase and appears a meso-α scale temperature ridge in the upper troposphere, which is feeded by mesoscale system in large scale back ground. Second, based on the successful control experiment, the sensitivity experiment of topographic effect is carried out. The results indicate that: on the north-west flow pattern in the upper troposphere, there are a stronger cold advection in the upper troposphere and an frontogenesis band caused by the topographic forcing in the lower troposphere, which is an important processes for the genesis and development of squall lines in North China.