The Diabatic and Nonlinear Aspects of the El Niño–Southern Oscillation: Implications for Its Past and Future Behavior
نویسنده
چکیده
This chapter reviews recent advances in understanding the diabatic and nonlinear aspects of the El Niño–Southern Oscillation (ENSO). In particular, it reviews the research leading to the view that averaged over the decadal or longer time scales, ENSO acts as a basin-scale heat mixer in the tropical Pacific. This heat mixer regulates the long-term temperature difference between the surface water in the warm pool and the subsurface water constituting the equatorial undercurrent. When this temperature difference is externally forced to increase, the level of ENSO activity increases. Conversely, when this temperature difference is externally forced to decrease, the level of ENSO activity decreases. The time-mean effect of ENSO is to counteract the effect of external forcing on this temperature difference. This view of ENSO explains the recent trend in the level of ENSO activity in the instrumental record and sheds light on the behavior of ENSO in the past climates. The implied response in the level of ENSO activity to global warming, however, is at odds with the popular prediction by the state-of-the-art coupled climate models. Reasons for this discrepancy are explored. An inadequate sensitivity of the tropical hydrological cycle to sea surface temperature changes in the present coupled models is hypothesized as a possible factor responsible for the discrepancy.
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تاریخ انتشار 2010