Modulation of Aleutian Low and Antarctic Oscillation co-variability by ENSO

Abstract

We use both the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis data (1979–2013) and the Community Atmospheric Model Version 3 to explore the modulation of El Nino–Southern Oscillation (ENSO) on the co-variability of the Aleutian Low (AL) and the Antarctic Oscillation (AAO). The empirical orthogonal function analysis on the NCEP–NCAR reanalysis data indicates that after the late-1990s the global sea level pressure (SLP) and 300-hPa geopotential height (Z300) in boreal January are characterized by the concurrence of the AL and the negative phase of the AAO (−AAO). Associated with this AL–AAO co-variation is a sea surface temperature anomaly that resembles the ENSO cycle. Further analyses reveal that the interdecadal change in ENSO signal (westward extension and more La Nina events) is responsible for the co-variability of AL and AAO after the late-1990s. Correspondingly, the El Nino-related anomalous heating and upward motion over the eastern–central equatorial Pacific can lead to the upper-tropospheric divergence in the western–central Pacific. This upper-tropospheric divergence plays an essential role in coupling the equatorial heat anomalies with the variation of the subtropical westerly jet of both hemispheres, and therefore results in the enhanced meridional circulation of the three cells. It thus implies that ENSO might act as a bridge linking AL and AAO after the late-1990s, causing their consistent co-variability. The numerical experiment also supports this hypothesis.