2019年春季我国主要气候异常特征及可能成因分析

Features and Possible Causes for the Spring Climate Anomalies in 2019

2019年春季(3-5月),全国平均气温为11.5℃,为1961年以来历史同期第四位;全国平均降水量为148.7 mm,接近常年同期,但旱涝分布差异显著。东北、西北地区东部和华南降水显著偏多,而黄淮、江淮及云南大部降水异常偏少,其中云南地区降水量为历史同期最少。气温偏高和降水空间分布不均导致旱涝灾害并存。季内气候变化显著,表现出东亚冬季风环流向夏季风环流转换期的特征。春季(尤其是3-4月)全国大部地区气温偏高受到中纬度环流型的明显影响,乌拉尔山及其以北地区为负高度距平中心,而乌拉尔山以东到贝加尔湖地区为大范围正高度距平,这种异常环流形势非常有利于我国气温整体偏高。另一方面,低伟度大气环流则表现出对热带海温异常的明显响应,西太平洋副热带高压(简称西太副高)异常偏强、偏西及偏南,这基本决定了我国春季降水异常的空间分布型,其强度和位置不仅能够直接影响南方降水分布,同时通过与中高纬异常环流的相互作用,共同影响我国北方降水异常格局。进一步分析热带海温外强迫的影响显示,在El Nino衰减年的春季,热带印度洋海温的增暖对西太副高持续偏强偏西起到更重要的作用;而El Nino事件本身对西太副高强度的影响在春季逐渐减弱,对西太副高南北位置的影响增强。

In spring 2019(March-April-May,MAM),the average temperature in China is 11.5℃,ranking the fourth in the same period since 1961.The average precipitation in China is 148.7 mm(near normal),with profound spatial differences.The precipitation is more than normal over Northeast China,east part of Northwest China and South China,but less than normal over Huanghuai,Jianghuai and most of Yunnan Province in MAM 2019.The MAM precipitation in Yunnan is the least since 1961.High temperature and uneven spatial distribution of precipitation lead to the coexistence of drought and flood disasters in MAM 2019.The sub-seasonal climate variability in spring 2019 is significant,showing the characteristics of the transition period from East Asian winter monsoon circulation to summer monsoon circulation.The high temperature in most China in spring(especially in March and April)is obviously affected by the mid-latitude circulation anomalies pattern.The Ural Mountains and to their north regions are the center of negative height anomaly,while the areas east of Ural Mountains to Lake Baikal are the center of positive height anomaly.Such an anomalous circulation pattern is very helpful to the overall high temperature in China.The atmospheric circulation systems present an obvious response to the tropical SST anomalies in MAM 2019.The western North Pacific subtropical high(WPSH)is strong,westward and southward extending,which basically determines the spatial pattern of spring precipitation anomaly in China.The intensity and location of WPSH not only directly control the pattern of precipitation anomaly in sou-thern China,but also affect the distribution of precipitation over northern China through the interaction of circulation anomalies in mid-high latitudes.Further analysis on the influence of tropical SST forcing shows that the warming of tropical Indian Ocean SST plays a more important role in the sustained strengthening and westward trend of WPSH in the El Nino decaying spring.The influence of the El Nino event on the intensity of WPSH gradually weakens in spring,and the effect on the north-south position of WPSH becomes more obvious.