Intraseasonal Atmospheric Variability in the Extratropics and Its Relation to the Onset of Tropical Pacific Sea Surface Temperature Anomalies

Abstract

Previous research has shown that seasonal-mean boreal winter variations in the subtropical/extratropical sea level pressure and wind stress fields over the central North Pacific are significantly related to the state of the El Niño?Southern Oscillation (ENSO) 12?15 months later. Results presented in this note indicate that boreal winter ENSO events are also preceded by increased intraseasonal variance in the antecedent boreal winter atmospheric circulation patterns over the extratropical central North Pacific as well. Low (high) surface pressure anomalies associated with intraseasonal variability in this region are related to intraseasonal wind stress anomalies that represent a weakening (strengthening) of the trade winds over both the north and south subtropical/tropical Pacific. There is also a concurrent increase (decrease) in the central and eastern subtropical North Pacific sea surface temperatures that projects onto the seasonal-mean SST anomalies that precede mature ENSO events by 9?12 months. Overall these results suggest that similar to seasonal-mean subtropical surface pressure and wind stress fields, enhanced transient variability in the midlatitudes can subsequently induce changes in the atmospheric and oceanic structure of the tropical Pacific that may serve as a precursor to ENSO variability.