春季北极地区云量跷跷板式的趋势变化特征及其对北极放大的云反馈作用

Seesaw Pattern of Arctic Cloud Cover Trend in Spring and Its Cloud Feedback Effect for Arctic Amplification

利用2000—2017年月平均的CERES云量、辐射资料和ERA再分析资料,对春季北极云量趋势变化特征和成因及其对北极放大反馈的贡献进行研究,发现春季北极地区总云量的趋势在东北极海区和北欧海区呈跷跷板式的反位相变化特征,并与低云量的趋势变化有较为一致的空间分布,中高云则与低云大体上呈相反的变化特征。北欧海的低云量减少、中高云增加,主要是因为进入北欧海区的超强气旋增多带来丰富的水汽,对流增强,云底高度抬升,使得低云量减少而中高云量呈增加趋势。这种云量垂直结构的变化所引起的云辐射强迫作用分别体现了低云的正反馈和中高云的负反馈作用,增温和降温作用相互抵消,使北欧海增温不显著。东北极海区低云量显著增加而中高云变化不明显,可能由于海冰融化,海表面增温,海面蒸发加强,水汽增加,大气静力稳定度减弱,有利于低云的形成。这种低云量的显著增加使得云辐射强迫作用强化了海冰反照率正反馈机制,从而加强了东北极海区的增温趋势。

Based CERES cloud cover,radiation data and ERA-Interim reanalysis data from 2000—2017 period,the characteristics,reasons and contribution to the Arctic amplification feedback of spring(March-May)cloud cover trend in Arctic are explored.A seesaw pattern of total cloud cover trend is found between the eastern Arctic Ocean and the Nordic Sea.Low cloud cover trend appears nearly consistent with the spatial pattern of the total cloud cover,and has almost opposite trend variation comparing to the middle-high cloud.Low cloud cover tends decreases,while the middle and high cloud cover tends increases in the Nordic Sea region,which is closely connected with the increasing super storm frequently entering the Atlantic sector and brings abundant water vapor.The storms also enhance convection,lift the cloud height and then results in the low cloud decrease and high cloud increase.The cloud radiative forcing effect caused by this cloud cover vertical structure mainly reflects a low cloud negative feedback and high cloud positive feedback effect,which cancels the warming and cooling effect for each other,inducing a non-significant warming trend in the Nordic Sea region.The low cloud shows a significant increasing trend in the eastern Arctic Ocean,while the middle-high clouds have no obvious trends.It may be related to the positive feedback process a warming results in sea ice melting and sea surface temperature increasing,then strengthens sea surface evaporation and increases water vapor in the air.The atmospheric static stability is weakened,which is conducive to the formation of low cloud.Increasing low cloud intensifies the positive feedback mechanism of the sea ice-albedo feedback through the cloud radiative forcing,thus warming effect is enhanced in the eastern Arctic Ocean.