青藏高原中东部云量变化与气温的不对称升高

Relations of Cloud Amount to Asymmetric Diurnal Temperature Change in Central and Eastern Qinghai-Xizang Plateau

利用ISCCP资料和地面观测资料,对1984 2009年青藏高原中东部云量和云状的气候特点进行了研究,并分析了日最高温度和日最低温度的变化特点及其与云量变化之间的关系。结果表明,青藏高原中东部地区中低云量呈明显的单峰型日变化,而高云云量日变化不显著;青藏高原地区日最低气温的上升速率与日最高气温不一致,即气温出现不对称升高。青藏高原中东部地区白天、夜间云的变化分别与日最高、最低气温的变化速率存在显著相关,并在云量变化与气温的不对称升高之间存在着正反馈机制。高原中东部地区不对称升温使得日出时的地气温差减小,并可能通过减弱对流作用使日出后的云量减少。云量的减少导致到达地面的太阳短波辐射增加,从而使得当日上午气温升高明显;中午,高云的增多与中低云的减少增加了地面接收的太阳短波辐射,导致了较高的日最高温度;而傍晚除卷云外,各类云的云量均出现增加,起到了减缓傍晚气温下降的作用,有利于出现较高的日最低温度。

By using ISCCP data and observation station data,the variations of cloud amount and cloud types are investigated in Central and Eastern Qinghai-Xizang Plateau（QXP）from 1984 to 2009;and the relationship between daily maximum/minimum temperature and cloud amount are analyzed.The results show that the diurnal variations of cloud amount at low-mid-level in QXP appears obviously unimodal types,but the diurnal variations of high-cloud amounts are not obviously.The warming rates of daily maximum/minimum temperature in TP are different,i.e,so called asymmetric diurnal temperature change.Diurnal/nocturnal cloud amount and daily maximum/minimum temperature have a distinct relation over Central and Eastern QXP,which have a positive feedback mechanism.The asymmetric temperature change reduces the difference of temperature between land and atmosphere in the morning,then the convection weakens,which may cause cloud amounts decreasing after sunrise.It will lead to much more solar shortwave radiation reaches the ground and the faster process of air warming in the morning.The decreasing of low-mid-cloud amounts and increasing of high-cloud amounts at noon increase the solar radiation of reaches the ground and causes a warmer daily maximum temperature.Cloud amounts of total cloud increase at dusk except cirrus,which slows down the decreasing rate of temperature after sunset,which benefits to increase the daily minimum temperature.