【摘要】 基于热带太平洋次表层海温资料,分析了热带太平洋第二类El Nio事件海温异常的分布特征及其形成机制,讨论了与经典El Nio事件、El Nio Modoki、WP(西太平洋暖池)及CT(冷舌)El Nio事件之间的关系,揭示了第二类El Nio事件对中国降水的影响,得到以下结论。(1)第二类El Nio事件表征为热带太平洋次表层海温异常第三模态,占总方差贡献的4.7%。在海洋表面层,第二类El Nio事件暖期赤道东太平洋为沿赤道西伸的冷舌,热带中西太平洋为环绕冷舌的马蹄型大范围暖区。该型具11a和30~40a年代际振荡及3~4a年际变率,峰值多出现在春季。第二类El Nio事件是热带太平洋异常海面风应力场和赤道两侧的风应力旋度共同作用的结果,在赤道东印度洋-中西太平洋与赤道东太平洋-南美洲上空出现以反号垂直运动为特征的异常Walker环流。(2)El Nio Modoki与第二类El Nio事件有密切关系,它实质上是第二类El Nio事件次表层海温与近海面大气相互作用的结果,捕捉了第二类El Nio事件的主要信息。(3)第二类El Nio事件对中国春季及夏初降水有一定影响。在事件暖期,东海地区存在一个显著的异常反气旋性环流,其南侧的中国南方地区盛行异常东北气流,水汽来源减少,导致该地区少雨,其西侧的异常偏南气流北上直达华北地区,异常多水汽向北输送,并与北方的偏北流场相遇,导致该地区降水偏多。在第二类El Nio事件冷期相反。本文结果还指出,WP与CT El Nio事件是由经典El Nio事件第一模态与El Nio Modoki事件组合而成,它们不是独立的El Nio类型。此外,还讨论了夏半年El Nio事件对大气环流影响的物理过程。更多还原

【Abstract】 Based on subsurface sea temperature datasets in the tropical Pacific,we analyze the spatial patterns and formation mechanism of the second-type El Nio events,and discuss its relationship with the classic El Nio event, El Nio Modoki,WP-and CT-type El Nio events.Also revealed is the impact of the second-type El Nio events on the precipitation variations in China.Results are summarized as follows.(1)The second-type El Nio event is the third EOF mode of subsurface temperature anomalies(SOTA)in the tropical Pacific,which explains 4.7%of the total variance.At the warm phase of this mode,sea surface temperature anomalies(SSTA)is composed of an anomalous warming in the central tropical Pacific flanked by an SST to the east that is a cold tongue strengthening westward along the equator in the eastern Pacific.This mode has a interannual period of 3—4year and 11and 30—40years long terms periods,with most mode peaks occurring in spring.The second-type El Nio events result from the combined effects of the anomalous sea surface wind stress in tropical Pacific and the wind stress curl on both sides of the equator,accompanied with anomalous Walker-circulation which are characterized by reversing vertical motions between the eastern Indian/western Pacific and the eastern Pacific/South America near the equator.(2)El Nio Modoki is shown to be closely associated the second-type El Nio event.It results from the air-sea interaction and catches primarily message of the second-type El Nio events.(3)The second-type El Nio events also influence the precipitation in China during spring and early summer.At its warm phase,an anomalous anti-cyclone develops over the East China Sea.Its southern flank results in anomalous northeast winds and reduced precipitation in the southern China.Its western flank transports more than normal vapor to the northern China,which confluences with the north winds,leading to more precipitation in this region.The opposite is valid at its cold phase.Moreover,we show that WP-and CT-type El Nio events are not independent El Nio types,but barely combinations of the classical El Nio and El Nio Modoki.Also addressed in this study are the physical processes of the influence of El Nio events on atmospheric circulation in summertime.更多还原