Extended Abstract (916K)6.3
The correlative evolution of upper ocean seasonal cycle and ENSO
Heng Xiao, Dept. of Atmos. and Oceanic Sci., UCLA, Los Angeles, CA; and C. R. Mechoso
The correlative evolution of the seasonal cycle in the upper ocean (outside of the surface layer) and ENSO is examined by performing idealized experiments with an Ocean General Circulation Model (OGCM). In the experiments, the fluxes of heat and momentum at the ocean surface are taken from a) a simulation in which the OGCM, coupled to an Atmospheric GCM (AGCM), produced realistic ENSO variability, or b) NCEP reanalysis data corrected by COADS climatology. The non-seasonal (interannually varying) component of the forcing is identical in the OGCM experiments, but the seasonal component is shifted in relation to the non-seasonal component in the experimental runs (SHIFT experiments). The shifting would make no difference in the results if the system were linear. From the 20-year simulation forced with NCEP reanalysis surface fluxes (1980-1999) and 16-year simulation forced with CGCM generated surface fluxes and the experimental runs, it is found that the response to shifting in terms of eastern basin heat content can reach 20-40% of the maximum anomaly. Budget analysis of one warm event case shows that anomalous zonal advection in the equatorial band is responsible. Additional experiments suggest that both locally and remotely forced signals (with delays) contribute significantly to the difference. It is concluded that the correlative evolution of the seasonal cycle in the upper ocean and ENSO includes significant nonlinear interactions between equatorially trapped wave signals related to ENSO anomalies and the seasonally varying upper ocean mean currents and thermocline structure.
Session 6, Unresolved issues in ENSO dynamics and prediction
Tuesday, 21 August 2007, 10:30 AM-12:00 PM, Broadway-Weidler-Halsey
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