Using South Pacific Climate Variability to Improve Seasonal ENSO Forecast Skill — Australian Meteorological and Oceanographic Society
  1. Schedule
  2. 34(iii). Tropical climate variability: dynamics, teleconnections and impacts
  3. Using South Pacific Climate Variability to Improve Seasonal ENSO Forecast Skill

Using South Pacific Climate Variability to Improve Seasonal ENSO Forecast Skill (#204)

Jason Furtado 1 , Yujia You 1 2
  1. University of Oklahoma, Norman, OK, United States
  2. Columbia University, New York City, New York, United States

While substantial advances in forecasting the El Niño-Southern Oscillation (ENSO) phenomenon have occurred in recent decades, skillful long-lead predictions of the strength and flavor (i.e., eastern vs. central Pacific) of ENSO events remains an open challenge. Past studies have considered several extratropical and tropical precursors in the atmosphere and ocean to improve the skill of these forecasts, but most of these have been North Pacific-centric. This presentation uses data from reanalysis and output from subseasonal-to-seasonal forecast models that South Pacific oceanic and atmospheric climate variability contribute substantially to ENSO variability and event evolution. Indeed, austral winter (June–August; JJA) variability associated with the South Pacific Oscillation (SPO), a meridional dipole in sea level pressure anomalies in the Southeast Pacific and a key driver of the South Pacific Meridional Mode (SPMM), contributes significantly to the structure and strength of an ENSO event the following November–January (NDJ). Findings indicate that while tropical Pacific SST anomalies have a remote influence on the extratropical South Pacific atmosphere, variability in the strength of the JJA South Pacific subtropical high (one node of the SPO) is highly intrinsic. This intrinsic component generates stochastic zonal wind stresses in the equatorial Pacific that influence ENSO development by affecting wave propagation and consequently the activation of the Bjerknes feedback. As such, the intrinsic component of the SPO is a significant source of the ensemble-spread in both the magnitude and location of NDJ forecasts of tropical Pacific SST anomalies associated with ENSO events. Additionally, in-phase and out-of-phase relationships between the North Pacific Meridional Mode and the SPMM also strongly influences the occurrence, amplitude, and the flavor of an ENSO event. Taken together, the prospects for improved long-lead ENSO forecasts are indeed possible. Specific cases and an application to the 2018-19 season are also discussed.

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