北极海冰融化与东亚春季降水量的联系

Relationship between Arctic sea ice melt and spring precipitation over East Asia

本文利用NCEP/NCAR等再分析资料和CAM5.4数值模式,研究了春季北极海冰融化面积对东亚降水量的影响及其可能的物理机制。观测和数值模拟结果均显示,与春季海冰融化相关的东亚地区降水量呈现明显增加的趋势,且异常中心位于中国南部-日本地区。500 hPa位势高度场表现为“-+-+”型波列结构,其中乌拉尔山和日本及其附近海洋上空为异常高压脊区,欧洲西部和贝加尔湖地区则为异常高空槽所控制。高融化面积年常伴随着极地西风急流增强,中纬度纬向西风减弱,有利于乌拉尔山地区反气旋性环流异常的维持和增强,进而触发乌拉尔山地区到西北太平洋地区的异常波列,引起贝加尔湖地区位势高度降低,东亚槽加深,受异常偏北气流的影响,南下冷空气活动频繁。日本及其附近的海洋上空位势高度增加,在异常偏东南气流的作用下,将西北太平洋地区的暖湿空气带到东亚地区。中国南部地区出现西风异常,引起东亚副热带急流增强,配合低空辐合高空辐散的大气异常环流,局地对流增强,导致东亚地区春季降水量增加。

This study investigates the association of spring(April-May)Arctic sea ice melt area with simultaneous precipitation over East Asia from 1979 to 2020 by using observational datasets and the Community Atmospheric Model version 5.4.The Arctic sea ice melt area exhibits interannual variability during the study period,and simulation experiments forced by Arctic sea ice anomalies reproduce the major characteristics of observational associations.Observed evidence and numerical experiment results show that spring precipitation anomalies associated with Arctic sea ice melt display an increasing trend over East Asia.Correlation analysis reveals that the Arctic sea ice melt area could be explaining approximately 26%precipitation variation over East Asia.The 500 hPa geopotential height anomalies exhibit a wave train structure,and a dominant positive center is located over the Ural Mountains with two negative centers over East Asia and West Europe.This atmospheric circulation anomaly is different from the traditional Eurasian pattern and North Atlantic-Eurasian teleconnection pattern owing to their different spatial modes.High Arctic sea ice melt years are often associated with strengthens polar zonal westerly winds and weakens zonal winds in mid-latitude.It may contribute to the Arctic anticyclonic anomalies enhancement,reduce cloud cover and enhance the Arctic incoming shortwave radiation in the spring,leading to an increase in surface air temperature in the Arctic,which in turn favor sea ice melt,a positive ice-albedo feedback process emerges.Then,the enhanced anticyclonic circulation anomaly induces a wave train southeastward propagating into the mid-low latitudes,causing the decrease of geopotential over the Lake Baikal,resulting in a cyclonic circulation anomaly,affected by the anomalous northerly flow,it is conducive to southward and accumulation of cold air.At the same time,Japan and its surrounding seas geopotential increasing,leading to an anticyclonic circulation anomaly,affected by the anomalous southeasterly flow,warm and humid air from the northwest Pacific Ocean can be brought to East Asia.For the high melt years,such a wave train pattern is usually associated with an anomalous low-pressure center over the Mongolian Plateau,which accelerates the East Asian subtropical westerly jet.The intensified subtropical westerly jet,concurrent with lower-level convergence and upper-level divergence,enhances the local convection and consequently favors rich spring precipitation over East Asia.