北极海冰对中国西北地区东部主汛期7月降水分布型的可能影响

The Possible Influence of Arctic Sea Ice on the Precipitation Distribution Pattern of July in East of Northwest China

选取1961-2020年中国西北地区东部154个气象站7月降水、NCEP/NCAR大气再分析及北极海冰资料,利用SVD分解等统计诊断方法,分析了北极关键区海冰对西北地区东部主汛期7月降水主要模态分布型的可能影响途径。结果表明:影响西北地区东部7月降水异常分布型主要有两种海冰模态,一种是当巴伦支海、千岛群岛海域海冰密集度偏小(大),戴维斯海峡海冰密集度偏大(小)时,激发从戴维斯海峡向东南以及从鄂霍次克海向西南方向传播的波列,使得我国西北地区东部上空500 hPa位势高度场距平为“西高东低”(“西低东高”)的分布,造成区域降水异常为“一致偏少(多)”分布型;另一种当波弗特海东海域海冰密集度偏小时,激发从里海东传至鄂霍次克海的波列以及配合我国华南上空的正位势高度异常,使得冷空气路径偏东、偏南以及西太平洋副热带高压偏强,造成研究区降水异常为“北少南多”分布型,反之为“北多南少”分布型。利用“SVD投影法”建立的海冰关键区因子预测模型,其对西北地区东部主汛期7月的降水距平符号的把握及空间分布型具有一定的预测能力,尤其对“区域一致少型”和“北多南少型”的预测效果较好。

Using the observed precipitation data of 154 meteorological stations in East of Northwest China,NCEP/NCAR atmosphere reanalysis and Arctic sea ice data from 1961 to 2020,the possible impacts and mechanisms of the key area Arctic sea ice on the main distribution mode of precipitation in July during the main flood season in East of Northwest China was analyzed using SVD and other climatic statistic methods.The results show that there are two mainly sea ice modes influencing the distribution pattern of precipitation anomaly in July in East of Northwest China.One is that when the sea ice density in the Barents Sea and the Kuril Islands is relatively small(large),and that in Davis Strait is relatively large(small),wave trains propagating southeastward from the Davis Strait and southwestward from the Sea of Okhotsk are stimulated,resulting in the anomaly field of"high in the west and low in the east"("low in the west and high in the east")at the 500 hPa geopotential height anomaly field over the East of Northwest China,which leads to the regional precipitation anomaly exhibiting a"consistent less(more)"pattern.The other is that when the sea ice density in the eastern part of the Beaufort Sea is relatively small,the wave train from the Caspian Sea to the Okhotsk Sea is stimulated and matched with the positive geopotential height anomaly over South China,making the cold air path eastward and southward,as well as the subtropical high stronger,which together lead to the precipation characterized by"less in the north and more in the south",on the contrary,the pattern of precipitation anomaly is reversed.The prediction model,which is established with sea ice in key areas as the prediction factors derived by“SVD projection method”,has certain prediction ability for grasping the precipitation anomaly trend and the spatial distribution pattern of the main flood season in July in East of Northwest China,especially for the"regional consistent less type"and"north more and south less type".