"Activity of the Southern Annular Mode during the Strong El Niño 2015-2016: less unusual than it used to be?"

MARISOL OSMAN

Oslo

Workshop; Workshop on physical modeling supporting a ?storyline approach?; 2019

Center for International Climate Research

Inthis work we analyzed the strong positive phase of the SouthernAnnular mode (SAM) observed during the El Niño event of 2015-2016(EN15-16) and impact on climate anomalies in the western portion ofthe Southern Hemisphere. Previous studies documented that El Niño(EN) events are in general associated with negative phases of theSAM. However, despite EN15-16 was one of the three strongest eventsever recorded, it was associated with SAM positive phases of extremeintensity. Furthermore, while the negative linear relationshipbetween ENSO and SAM during the most recent period (1986-2014) wassignificant and associated with a narrow uncertainty band, thecombined condition of both climate patterns in the EN15-16 event wasan outlier. In addition, while SAM anomalies during 2015 australspring (September-October-November) can be attributed to the extremenegative ozone anomalies in the Southern Hemisphere (SH), the reasonsfor the strong positive anomalies in austral summer(December-January-February) are still unclear. TheEN15-16 influence on the austral summer circulation anomalies at theextratropical and polar regions of the SH was considerably altered bythe strong SAM positive phase, which was evident not only at thetroposphere but also at the stratosphere. The analysis of thegeopotential heights anomalies at 200hPa reveals that in the EN15-16event, large negative anomalies were well discernible over theAntarctica, that are typical of SAM positive phases. In addition,negative centers located over central and eastern portions of thesouth Pacific middle latitudes and the positive center extended tothe west of the Antarctic Peninsula are shifted equatorward in theEN15-16 than in the other EN composites. Such circulation changesresulted in unusual regional impacts.Theunusual behaviour of the SAM during the last EN and the projectedchanges of SAM during the 21stperiod, as a consequence of GHG emissions and Ozone recovery, open upmultiple questions around the future of ENSO-SAM relationship and itsimplication in the climate anomalies observed in the SH.p { margin-bottom: 0.1in; direction: ltr; color: #000000; line-height: 115%; orphans: 2; widows: 2 }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; so-language: en-US }p.cjk { font-family: "Noto Sans CJK SC Regular"; font-size: 12pt; so-language: zh-CN }p.ctl { font-family: "Lohit Devanagari"; font-size: 12pt; so-language: hi-IN }