Signal of central Pacific El Niño in the Southern Hemispheric stratosphere during austral spring

Abstract

AbstractUsing ERA‐Interim and Modern‐Era Retrospective Analysis for Research and Applications reanalysis data sets, we investigated the effects of the central Pacific (CP) El Niño on the Southern Hemispheric (SH) stratosphere particularly during the austral spring. SH stratosphere warming is at a maximum in September rather than in November and December, as suggested by previous studies. SH stratospheric temperature anomalies become significant beginning in July and reach a peak of approximately 4 K in September, reflecting a weakened SH vortex and a strengthened SH stratospheric Brewer‐Dobson circulation. The anomalous Eliassen‐Palm flux and its divergence in the SH midlatitudes are most significantly enhanced in August, leading to the SH maximum stratospheric temperature anomalies approximately 1 month later. In the middle latitudes of the SH, the poleward and upward propagation of enhanced planetary waves (PWs) during the austral winter (July–September) causes anomalous SH polar warming and tropical cooling in the stratosphere. The wave number 1 (WN1) pattern is responsible for PW anomalies in August, whereas the WN2 pattern is responsible for those in September. Eddy heat flux during CP El Niño is also anomalously enhanced in extratropical SH stratosphere in both August and September and subsequently weaken during the following months.