Thermodynamic Triggering Mechanism of ENSO -- A Coupled Model Study

Abstract

Much of the literature on the study of ENSO has been directed towards understanding of dynamic aspect of the coupled system. The thermodynamic aspect of ENSO physics is less studied and less understood.

In this study, we examine the thermodynamic aspect of ENSO physics in some detail with the aid of a newly developed coupled model consisting of an atmospheric general circulation model (CCM3.6) and a Zebiak-Cane type of Reduced Gravity Ocean (RGO) model. Among the many novel features of this coupled model is a noise filter algorithm designed to suppress internal atmospheric variability in the coupled system in order to directly assess the role of internal atmospheric variability in ENSO dynamics. Extensive numerical experiments have been conducted. The results show that this modeling tool can not only give a realistic simulation of ENSO, but also provide an effective means to delineate the dynamic vs the thermodynamic contribution to ENSO.

Several important findings emerge from this study:

• Thermodynamic coupled feedback linked to the ITCZ variability in boreal spring seems to work as a conduit between internal atmospheric variability and ENSO
• This coupled variability appears to play an important role in the seasonal phase-locking of ENSO
• Surface heat fluxes induced by internal atmospheric variability has a more dramatic effect on ENSO than the corresponding surface momentum fluxes