GEOPHYSICAL MONOGRAPH SERIES, VOL. 147, PP. 71-83, 2004
The control of meridional differential surface heating over the level of ENSO activity: A heat-pump hypothesis
NOAA-CIRES/Climate Diagnostics Center, Boulder, Colorado
Numerical experiments with a coupled model have been carried out to test the heat-pump hypothesis for ENSO. The hypothesis
states that the level of ENSO activity is controlled by the meridional differential surface heating over the Pacific: either
an enhanced surface heating over the equatorial region or an enhanced cooling over the subtropical/extratropical ocean may
result in a regime with stronger ENSO events. Moreover, ENSO may b e a mechanism that regulates the long-term stability of
the coupled equatorial ocean-atmosphere system. The results from the numerical experiments are shown to b e consistent with
this hypothesis. A stronger tropical heating or a stronger subtropical/extratropical cooling tends to increase the contrast
between the SST in the tropical western Pacific warm-pool and the temperature of the equatorial thermocline water and thereby
destabilize the coupled equatorial ocean-atmosphere system. In response, a regime with stronger ENSO events sets in. The stronger
ENSO events transport more heat downward and poleward, cooling the warmpool SST and warming the equatorial thermocline water.
In the presence of ENSO, the difference between the time-mean warm-pool SST and the time-mean temperature of the equatorial
thermocline water is found to be insensitive to changes in the external forcing.
Citation: Sun, D.-Z. (2004), The control of meridional differential surface heating over the level of ENSO activity: A heat-pump hypothesis, in Earth's Climate: The Ocean-Atmosphere Interaction, Geophys. Monogr. Ser., vol. 147, edited by