Abstract:

The numerical simulation and diagnosis of extreme drought events is an important method to test the performance of regional climate model and study drought mechanism. The extreme drought event occurring in spring of 1995 in Northwest China was simulated by RegCM4 model, firstly. Based on the NCEP reanalysis data and monthly precipitation data from 137 weather stations in Northwest China, the effect of the extreme drought event  simulated by RegCM4 model was tested. And on this basis the formation mechanism of the extreme drought event was analyzed by using wave-flow theory. The results show that RegCM4 model could simulate the spatial distribution of drought grades of the extreme drought event better, but the errors between the simulated and the observed were different in different areas, and it could also accurately simulate the main influence climate system, which indicated that the model had a good reappearance ability to the extreme drought event. The downward flow in Northwest China enhanced due to the stronger Ural mountain high pressure and the Mongolian low pressure in spring of 1995. Meanwhile, the water vapor flux decreased significantly compared with the normal year because the strong westerly airflow in low level impeded the water vapor transport to the region of Northwest China. The analysis of wave-flow theory indicated that there was a wave-train transporting from west to east on 300 hPa, and the transient wave energy reached the maximum in Ural mountain area in April. The divergent E-P flux caused the enhancement of the westerly jet in the north of the Ural mountain high pressure ridge, which led to the development and maintenance of the Ural mountain high pressure, thus caused the extreme drought event.

摘要：

极端干旱事件的模拟和诊断是检验区域气候模式性能、研究其发生机制的重要途径。利用区域气候模式RegCM4对1995年我国西北地区典型的春季极端干旱事件进行数值模拟，并基于NCEP再分析格点资料和西北地区137个测站的降水量资料对模拟效果进行检验，在此基础上，采用波—流理论对此次极端干旱事件发生机制进行分析。结果表明：区域气候模式RegCM4能够较好模拟出此次极端干旱事件的干旱等级空间分布特征，但不同区域的模拟误差有差异；对造成此次极端干旱事件的主要天气气候影响系统模拟非常准确，表明该模式对此次极端干旱事件发生过程具有很好的再现能力。由于1995年春季乌拉尔山高压、蒙古低压偏强，使得我国西北地区辐散下沉气流增强，加之低层强西风气流阻碍水汽的输送，从而使得西北地区水汽通量较常年显著偏小。波—流理论分析表明，300 hPa存在自西向东传的波列，且4月瞬变波能量在乌拉尔山区域达到最大，中层乌拉尔山高压脊以北区域辐散的E-P通量导致该区域西风急流增强，是乌拉尔山高压得以发展和维持的原因，从而造成了此次极端干旱事件。

关键词: 极端干旱事件∣数值模拟∣波&mdash, 流作用