青藏高原南侧经圈环流变化特征及其对降水影响分析

Characteristics of Meridional Circulation Cell on the South Side of Qinghai-Tibetan Plateau and its Effects on Precipitation over the region

基于1979-2015年青藏高原(下称高原)地区气象观测站的逐日降水资料和ERA-Interim逐日再分析资料,分析高原南侧经圈环流的季节演变及年际变化特征,并讨论其对高原降水及水汽输送的影响。结果表明,高原南侧80°E-90°E范围存在前季风环流、季风环流、Hadley环流的季节演变,前季风环流有-0. 377 s^(-1)·(10a)^(-1)减弱的趋势,季风环流有0. 524 m·s^(-1)·(10a)^(-1)显著增强趋势。在90°E-105°E范围存在季风环流和Hadley环流季节转换,季风环流存在0. 413 m·s^(-1)·(10a)^(-1)的增强趋势。基于各经圈环流开始、结束时间的定义,发现在80°E-90°E,前季风环流建立的时间有推迟而结束时间有提前的现象,其维持时间出现每10年-1. 47候的缩短趋势。在90°E-105°E,季风环流维持时间增长,Hadley环流维持时间缩短。前季风环流增强使得高原水汽辐散区辐散增强,水汽辐合区辐合增强,高原西南侧有东北向水汽输送增强,而高原西北侧有西南向水汽输送增强。夏季季风环流增强,高原南部至孟加拉湾地区自南向北的经向水汽输送显著增强,印度洋向高原输送的西南向水汽通量明显增加。前季风环流增强,春季高原中部及西南部降水减少,而东南部和北部降水增加。夏季季风环流增强时,高原南侧上升支增强,高原南部降水增加,而高原北部降水出现减少。

Based on the daily observational precipitation data and ERA-Interim daily reanalysis data from 1979 to2015,the meridional circulation cell characteristics on the south side of Qinghai-Tibetan Plateau and its effects on precipitation and water vapor transport over the Qinghai-Tibetan Plateau had been investigated.The results are shown as follows:The pre-monsoon circulation,monsoon circulation and Hadley circulation constitute seasonal evolution of meridional circulation cell on the south side of Qinghai-Tibetan Plateau along 80°E-90°E.A decreasing trend is observed with a rate of-0.377 s-1·(10a)-1 in the intensity of pre-monsoon circulation,while an increasing trend is detected with a value of 0.524 m·s-1·(10a)-1 in the intensity of monsoon circulation.There exists the transition of monsoon circulation and Hadley circulation on the south side of Qinghai-Tibetan Plateau along 90°E-105°E.The intensity of monsoon circulation remarkably increases during 1979-2015 with a trend of 0.413 m·s-1·(10a)-1.According to the definition of building and ending time of each meridional circulation cell,the setup of pre-monsoon circulation is delayed and the ending time is advanced and hence the maintaining time of pre-monsoon circulation trends to be shortened.Along the 90°E-105°E,the maintaining time of monsoon circulation shows an increasing trend while the maintaining time of Hadley circulation presents a decreasing trend.When the pre-monsoon circulation becomes stronger,the water vapor in divergence region trends to divergent and the water vapor in convergence region trends to convergent.Moreover,north-east water vapor transport is increased on the southwest Tibetan Plateau and south-west water vapor transport is enhanced on the northwest Qinghai-Tibetan Plateau.The strong summer monsoon circulation is beneficial to northward water vapor transport in the southern Tibetan Plateau and the Bay of Bengal and south-west water vapor transport from the Indian Ocean to the Tibetan Plateau.The precipitation is decreased in the middle and southwest Qinghai-Tibetan Plateau,whereas increases in the southeast and north of the Qinghai-Tibetan Plateau are clear as pre-monsoon circulation is enhanced.When summer monsoon circulation is strengthened,the more/less rainfall occurs in the south/north of Qinghai-Tibetan Plateau.