The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the ye...The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.展开更多
利用1951—2017年NOAA月平均海面温度、NCEP/NCAR的再分析资料以及中国160站月降水观测资料,通过分类合成分析方法研究了东部型(eastern Pacific,EP)和中部型(central Pacific,CP)厄尔尼诺(El Nino)事件当年及次年对山东夏季降水年际变...利用1951—2017年NOAA月平均海面温度、NCEP/NCAR的再分析资料以及中国160站月降水观测资料,通过分类合成分析方法研究了东部型(eastern Pacific,EP)和中部型(central Pacific,CP)厄尔尼诺(El Nino)事件当年及次年对山东夏季降水年际变化的影响。结果表明,两类El Nino发生年,山东夏季降水均较常年显著偏少,但EP El Nino对山东夏季降水的影响强度和范围略弱于CP El Nino:EP El Nino发生年夏季,仅鲁西北部分地区以及胶州湾附近降水较常年显著偏少,而CP El Nino当年夏季山东全区降水较常年显著偏少。EP El Nino和CP El Nino次年对山东夏季降水异常的影响呈反位相,且影响大值区空间位置也完全相反:EP El Nino次年夏季山东东部尤其是半岛地区降水较常年异常偏少(青岛地区最为突出),而CP El Nino次年夏季山东中部和北部尤其是西北部地区降水较常年异常偏多。EP El Nino当年和次年夏季、CP El Nino当年夏季500 hPa高度场异常分布形势不利于西北太平洋副热带高压的北上,850 hPa风场为偏北风和偏东风异常,山东水汽输送条件差,水汽无明显辐合,造成大部分地区降水偏少。CP El Nino次年夏季西北太平洋副热带高压偏强,位置偏西偏北,850 hPa显著西南风场异常,山东中西部水汽辐合明显,这些是降水偏多的重要原因。展开更多
基金funding support from the National Monsoon Mission program of the Ministry of Earth Sciences(MoES),New Delhi。
文摘The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.
文摘利用1951—2017年NOAA月平均海面温度、NCEP/NCAR的再分析资料以及中国160站月降水观测资料,通过分类合成分析方法研究了东部型(eastern Pacific,EP)和中部型(central Pacific,CP)厄尔尼诺(El Nino)事件当年及次年对山东夏季降水年际变化的影响。结果表明,两类El Nino发生年,山东夏季降水均较常年显著偏少,但EP El Nino对山东夏季降水的影响强度和范围略弱于CP El Nino:EP El Nino发生年夏季,仅鲁西北部分地区以及胶州湾附近降水较常年显著偏少,而CP El Nino当年夏季山东全区降水较常年显著偏少。EP El Nino和CP El Nino次年对山东夏季降水异常的影响呈反位相,且影响大值区空间位置也完全相反:EP El Nino次年夏季山东东部尤其是半岛地区降水较常年异常偏少(青岛地区最为突出),而CP El Nino次年夏季山东中部和北部尤其是西北部地区降水较常年异常偏多。EP El Nino当年和次年夏季、CP El Nino当年夏季500 hPa高度场异常分布形势不利于西北太平洋副热带高压的北上,850 hPa风场为偏北风和偏东风异常,山东水汽输送条件差,水汽无明显辐合,造成大部分地区降水偏少。CP El Nino次年夏季西北太平洋副热带高压偏强,位置偏西偏北,850 hPa显著西南风场异常,山东中西部水汽辐合明显,这些是降水偏多的重要原因。
