海冰和海温对西北地区中部6月降水异常的协同影响

Synergistic effects of ice and sea surface temperature on the precipitation abnormal in June in the central part of northwest China

利用1961年以来美国国家环境预报中心(NCEP)月平均再分析风场、高度场、NOAA重构海表温度以及西北地区中部54个气象站6月逐日降水资料、1979年以来北极10个区域的海冰面积,通过分析2019年6月西北地区中部降水异常的成因,揭示出对该区域6月降水具有显著影响的关键海区海冰面积及时段、北大西洋三极子(NAT)关键影响时段,结合厄尔尼诺-南方涛动(ENSO)事件,分析其协同作用及影响机制。结果表明:1990年以来春季3-4月楚科奇海海冰面积异常容易激发欧亚中高纬度EU2(欧亚2型)遥相关型(即夏季EU(欧亚)遥相关型),有利于西北地区中部降水异常,1992年以来春季NAT对EU2遥相关型有明显影响,但其影响小于楚科奇海海冰面积的影响;当楚科奇海海冰面积偏少和NAT正位相(海冰面积偏多和NAT负位相)协同作用时,西北地区中部降水偏多(偏少)的概率明显增大;ENSO事件对西北地区中部6月降水无明显直接影响,但厄尔尼诺事件次年使得副热带高压异常偏强、偏西。2019年楚科奇海海冰面积异常偏少,春季NAT异常偏强,两者协同作用下使得EU2遥相关型正异常(“+-+-”),尤其使得贝加尔湖附近的阻塞高压异常偏强,鄂霍次克海和乌拉尔山附近低压异常深厚,厄尔尼诺事件使副热带高压异常偏强、偏西,将西太平洋的水汽输送至北太平洋,与鄂霍次克海附近的深厚低压相接,充足的冷空气和水汽导致西北地区中部出现异常降水。研究成果可为短期气候预测提供依据,同时,气-冰-海之间的相互作用需要更进一步研究。

Located at the hinterland of East Asia and the edge of Qinghai-Tibet Plateau,the central part of northwest China has complex terrain and diverse climate types.Most of the areas are rain-fed agriculture,which is also the most vulnerable area of the ecological environment.June is the critical period for summer grain crop growth,which has a great influence on climate.In June 2019,the amount and days of precipitation in most of the central part of northwest China were more accompanied by frequent heavy rainfall.At the same time,there was a rare continuous low temperature and rainy weather.Thus,based on the monthly average height field,wind field reanalysis data of the National Centers for Environmental Prediction(NCEP),NOAA reconstructed sea surface temperature since 1961,the daily precipitation data of 54 weather stations in the central part of northwest China in June,and the sea ice area of ten regions in the Arctic since 1979,the causes of precipitation anomaly in the central part of northwest China in June 2019 was analyzed.The key sea ice areas and period,the key periods of the North Atlantic Triple(NAT)that have a significant impact on the precipitation in June were investigated.Furthermore,the synergistic effect and influence mechanism between the sea ice areas and the NAT with ENSO event were analyzed.The results showed that the correlation between precipitation and altitude field in the central part of northwest China changed significantly in June.Also,the precipitation was abnormal more when the distribution of height anomaly field in middle and high latitudes was the Eurasian 2 pattern(EU2)teleconnection pattern(i.e.,summer EU(Eurasian)teleconnection type)since the 1990s.The precipitation was more when the EU2 is positive phase“+-+-”,and vice versa.The influence of the sea ice area in the Chukchi Sea from March to April and the NAT in spring on 500 hPa altitude field changed significantly since 1990 and 1992,respectively.It had a significant influence on the EU2 teleconnection pattern,but the influence of NAT is less than that of the Chukchi Sea ice area.When the sea ice area was less and NAT positive phase(sea ice area more and NAT negative phase),the probability of more(less)precipitation in the central part of northwest China increased obviously.ENSO events had no obvious direct impact on the precipitation,but the subtropical high was anomaly stronger and westward in the next year of the El Nino event.The Chukchi Sea ice area was abnormally small with a strong positive phase NAT in spring in 2019,which made the EU2 teleconnection positive anomaly.El Nino event transported water vapor from the Western Pacific Ocean to the North Pacific Ocean,which cooperated with EU2 teleconnection made the cold air and water vapor were enough to make abnormal precipitation in the central part of northwest China.The research results could provide a basis for short-term climate prediction.While all the relationship between the precipitation in June,sea ice area from March to April,NAT in spring,and altitude field in the central part of northwest China had changed since the 1990s,then the interaction of them(air-ice-sea)needs further study.