秦岭及周边地区夏季降水的主模态分析

基于秦岭及周边地区394站气象观测资料、欧洲中期数值预报中心(ECMWF)再分析ERA-Interim数据,利用小波和回归等分析方法,讨论了秦岭及周边地区夏季降水年际变化的主模态以及与其相联系的大气环流异常。结果表明:1)在年际变化的时间尺度上,秦岭及周边地区夏季降水主要表现为秦岭南北降水的气候差异性变化(EOF1)、黄土高原第二地形抬升带与其两侧降水的反位相振荡(EOF2)、秦岭西南部降水正异常和其东北部降水负异常变化(EOF3)和关中平原的地形降水贡献(EOF4)4个模态,其解释方差总贡献为73%,并且具有显著的2~4 a周期,其中EOF3和EOF4还具有4~8 a左右的年际变化周期。2)回归分析表明,EOF1正位相环流特征表现为200 hPa急流偏弱,中纬度槽填塞,西太平洋副热带高压强度偏弱,有来源于东海的水汽输送,使得秦岭北部降水偏多;EOF2和EOF3分别具有显著的蒙古低压和东北冷涡环流特征;EOF4的500 hPa环流异常不显著。3)根据新定义的秦岭季风指数回归分析表明,回归场的季风指数和降水模态的时间系数显著相关,秦岭北部降水偏多(少),南部降水偏少(多),反映了强(弱)季风年的年际转换。反之则具有多态性,不同年份强(弱)秦岭回归季风指数的环流形势存在较大的差异,可能触发多种降水模态和位相振荡。

Dominant modes of summer precipitation in Qinling and surrounding areas

Based on the observed precipitation data from 394 stations over Qinling and surrounding areas,the ERA-Interim reanalysis data from the European Centre for Medium-range Weather Forecasts(ECMWF),the Empirical Orthogonal Function(EOF),wavelet and regression analysis methods,the major modes of summer precipitation in Qinling and surrounding areas and their associated atmospheric circulation anomalies are analyzed.Results show that:(1)The first four EOF modes account for 73% of the total variance and the principal component has significant interannual variability with 2-4 years period.EOF1 reflects the difference climate change between south and north Qinling.EOF2 reflects the reverse phase oscillation on both sides of the loess plateau.EOF3 is characterized by opposite distribution between southwest and northeast Qinling.EOF4 reflects Guanzhong plain topography precipitation contribution.The EOF3 and EOF4 also have 4-8 years interannual variations.(2)Regression analysis showed that when EOF1 in positive phase,200 hPa Jet is weak,at the same time,midlatitude trough and West Pacific subtropical high are weak,anomalous water vapor transport from East China Sea favors more precipitation in northern Qinling.EOF2 and EOF3 have significant Mongolia low and Northeast cold vortex circulation characteristics respectively.500 hPa circulation anomaly of EOF4 was not significant.(3)A summer monsoon index in Qinling is defined,the monsoon index of the regression field is significantly related to the time coefficient of the precipitation spatial mode,more(less) precipitation in Northern Qinling,less(more) rainfall in the South,reflecting the strong(weak) monsoon year conversion.Otherwise,in different strong(weak) monsoon years,the atmosphere circulation in Qinling has big difference,which can trigger a variety of precipitation mode and phase oscillations.