青藏高原东部边缘一次大暴雨发生机制研究

Research on the Mechanism of a Heavy Rain Occurred in the Eastern Edge of Tibetan Plateau

2007年8月25～26日青藏高原东部边缘发生1次成灾十分严重的大暴雨过程。利用NCEP(1°×1°)资料对暴雨的影响系统、水汽输送进行了分析,并用位涡理论对此次暴雨的发生机制进行了研究。结果表明:副热带高压边缘强盛的水汽输送,暴雨区上空强烈的水汽辐合是暴雨发生的重要原因,暴雨发生前的强烈不稳定为暴雨的发生提供了热力条件;此次暴雨过程中,西北冷低压槽在青海东部和甘肃中部影响较弱,它在气压场上表现不是很明显,仅在暴雨区附近形成弱风切变;而325K等熵面位涡对此次暴雨的发生系统具有明显的指示意义,高值位涡的冷空气沿着陡峭的等熵面下滑到底层,由于位涡守恒,从而促使低层垂直涡度急剧增大,从而导致了此次暴雨的发生。

A heavy rain occurred in the eastern edge of Tibetan Plateau during August 25-26 of 2007 resulted in serious disaster.The weather system and vapour transportation was analyzed by using NCEP（1° × 1°） data,and then the PV theory was used to study the mechanism of the heavy rain.The results show that the strong vapour transportation in the edge of the subtropical high and vapour convergence over the rainstorm area was the important reason for the rainstorm occurrence.The strong instability before the rainstorm provided benefit thermal condition.The northwest cold low trough had not obvious sign on the pressure field in the course of the rainstorm,which only formed a weak wind shear near the rainstorm area,and it had small effect on this heavy rain.But the 325 K isentropic surface had obvious indicating meaning for the rainstorm occurrence,when the cold air with higher PV value slided down to the low level along the steep isentropic surface,the vertical vorticity increased rapidly because of the conservation of PV,as a result,the heavy rain occurred.