两种积云参数化方案对青藏高原夏季降水影响的模拟

Simulation Influences of Summer Precipitation by Two Cumulus Parameterization Schemes over Qinghai-Xizang Plateau

利用区域气候模式RegCM4.0分析了Tiedtke和Emanuel两种积云对流参数化方案对青藏高原(下称高原)夏季降水模拟的影响,并利用JRA-25资料和NCEP资料作对比分析。结果表明,高原夏季降水呈南多北少分布,空间变化复杂;降水主要由对流产生,且有明显的逐日和逐月变化趋势;Tiedtke方案模拟的降水强度和分布范围较Emanuel方案和验证资料偏小,但对对流降水日变化模拟较好。对流层中下层大气的干湿状况对降水影响显著;垂直运动和水汽输送受地形影响大,高原中部、东部及西北部地区均有净的水汽输入;高原东南端的强上升运动区可伸至对流层中上层,其余地区垂直运动尺度较小;祁连山地区高层空气下沉、低层空气上升,是造成该地区降水较周边地区偏多的原因之一。本次试验还表明基于质量通量的积云对流参数化方案在高原地区虽具有一定适用性,但Tiedtke方案需很大改进,尤其是对小尺度对流活动的改进,从而提高其模拟能力。

The regional climate model RegCM4.0 was used to analyze the impacts of Tiedtke cumulus parameterization scheme and Emanuel scheme on summer precipitation simulation over Qinghai-Xizang Plateau,while JRA—25 data and NCEP reanalysis data were used as comparison.The experiment indicated that monthly average precipitation has a complex variation,and precipitation over Southern Qinghai-Xizang Plateau is much larger than Northern.Convective precipitation that accounts for a large proportion in total precipitation,has an obvious daily and monthly variation.Although precipitation simulated by Tiedtke scheme is less than Emanuel scheme,it still has a good performance on daily variation of convective precipitation.Precipitation simulation obviously affected by lower troposphere humidity.Topography has a great impact on water vapor and ascending motion simulation,and except for Southeastern Qinghai-Xizang Plateau where strong ascending motion can reach upper troposphere,the scale of vertical movement in other areas is smaller.The center of Qinghai-Xizang Plateau has net income of water vapor,and the reason why Qilian mountain has more precipitation than surrounding areas is that upper air sinks and lower air rises.The study also revealed that cumulus parameterization scheme based on mass flux has some applicability over Qinghai-Xizang Plateau,but Tiedtke scheme needs great modification,especially to modify the smaller scale convective process for improving simulation ability.