Untangling ENSO Precursors

Abstract:

There are several proposed precursors to the El Nino-Southern Oscillation (ENSO) that may provide the ability to predict ENSO as much as one year in advance. Some of these precursors are associated with stochastic forcing from extratropical atmospheric variability. Two examples are the seasonal footprinting mechanism (SFM) and the Pacific meridional mode (PMM). Both of these ENSO precursors are thought to be forced by the North Pacific Oscillation (NPO), a north-south sea level pressure dipole in the north Pacific. Additionally, both the PMM and SFM are thought to impact the tropics through wind evaporation SST feedbacks and have a correlation with ENSO up to one year in advance.

These two precursors are discussed interchangeably throughout the literature and various indices used to define them co-mingle them. As a result, whether they are independent of each other or are part of the same process has not been investigated. The research presented is focused on untangling the relationship between the PMM, SFM, NPO, and ENSO using observational datasets and model simulations. Observational results demonstrate that these two mechanisms are different, are forced by different atmospheric circulations, and result in different manifestations of ENSO. Modeling results highlight the extent to which climate models can simulate these relationships and their impact on the simulation of ENSO.