Activity of the Southern Annular Mode during 2015-2016 El Niño event and its impact on Southern Hemisphere climate anomalies

MARISOL OSMAN; CAROLINA VERA

Sydney

Conferencia; International Conference on the Southern Hemisphere Meteorology and Oceanography; 2018

AMOS

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 its impact on climate anomalies in the western portionof the 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, like negative anomalies ofsurface air temperature in western Antarctic Peninsula, and negativeprecipitation anomalies in southeastern South America, ever recordedfor previous strong EN events.p { margin-bottom: 0.1in; direction: ltr; color: rgb(0, 0, 0); line-height: 120%; }p.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; }p.cjk { font-family: "Noto Sans CJK SC Regular", "Times New Roman"; font-size: 12pt; }p.ctl { font-family: "FreeSans", "Times New Roman"; font-size: 12pt; }