Evaluating the Variability of the ENSO-SAM Teleconnection to Antarctica Using the NCAR CAM 4

Previous work has demonstrated how the El Nino-Southern Oscillation's (ENSO) teleconnection to Antarctica is modulated dynamically by the Southern Annular Mode (SAM). When ENSO and SAM anomalies are "in-phase" (La Niña/SAM+, El Niño/SAM-), the ENSO teleconnection to the high-southern latitudes is robust and enhanced. In contrast, when ENSO and SAM are “out-of-phase”, the teleconnection is weakened. Recent discussion on ENSO flavors continues as well, namely whether the central Pacific ENSO represents a distinct pattern of SST anomalies (“Modoki”) or if it is part of a larger ENSO evolution involving the canonical eastern Pacific ENSO. Despite the debate, several ENSO events occurred during the 1990s and 2000s where the Pacific SST anomalies were confined to the central Pacific Ocean. These events have been shown to affect winter storm tracks in the Southern Hemisphere and alter the typical teleconnection impacts across the globe. Using the National Center for Atmospheric Research Community Atmosphere Model (CAM 4), which captures important features of the observed ENSO-SAM teleconnection, the dynamical coupling is explored further with emphasis on the effect of central versus eastern Pacific SST anomalies on the phasing between ENSO and SAM. Two separate methods are utilized to investigate this relationship. First, strong and weak SAM cases are encouraged in CAM through a gentle nudging of the zonally-averaged circumpolar flow around Antarctica while the lower boundary SSTs, sea ice, ozone, and carbon dioxide based on observations from 1979-2005 are prescribed. Second, 15-year simulations with cyclical lower boundary conditions representing each phase of ENSO and ENSO flavors (canonical and Modoki) are conducted. Both sets of anomaly experiments are compared to appropriate control simulations in order to detail changes to the teleconnection through the positions and strengths of the subtropical and polar front jets as well as the variability of the ENSO-SAM phasing during the canonical ENSO versus Modoki ENSO events.