HR: 1300h
AN: OS52D-19    [PDF]
TI: The Effect of Subtropical Cooling on the Amplitude of ENSO: A Numerical Study
AU: * Sun, D
EM: dezheng.sun@noaa.gov
AF: NOAA-CIRES/Climate Diganostics Center, 325 Broadway, Boulder, CO 80304 United States
AU: Zhang, T
EM: tao.zhang@noaa.gov
AF: NOAA-CIRES/Climate Diganostics Center, 325 Broadway, Boulder, CO 80304 United States
AU: Shin, S
EM: sangik.shin@noaa.gov
AF: NOAA-CIRES/Climate Diganostics Center, 325 Broadway, Boulder, CO 80304 United States
AB: Theoretical, observational, and modeling studies have suggested the existence of an ``ocean tunnel''--the water constituting the equatorial undercurrent and therefore the upwelling water in the equatorial Pacific comes from the subtropical/extratropical region. The effect of an increase in the subtropical surface cooling on ENSO through this ``ocean tunnel'' is investigated using a coupled model. Except with a delay in the response of the ENSO, the cooling imposed outside of the equatorial region has the same effect as that from an enhanced equatorial heating on the amplitude of ENSO. An enhanced cooling in the subtropics is found to reduce the temperature of the water feeding the equatorial undercurrent. The resulting colder upwelling water destabilizes the coupled equatorial Pacific system because it tends to increase the equatorial zonal SST contrast between the eastern and western Pacific. In response to this destabilizing forcing, a regime with stronger ENSO develops. ENSO is again found to regulate the time-mean SST contrast between the eastern and western equatorial Pacific: the time mean SST contrast is insensitive to enhanced subtropical cooling. In the enhanced subtropical cooling case, more heat is transported out of the equatorial Pacific to the higher latitudes and the transport becomes more episodic. These findings provide further support for the ``heat-pump'' hypothesis for ENSO which states that ENSO is an instability driven by the meridional differential heating over the ocean and that ENSO regulates the stability of the coupled equatorial Pacific climate. The results also substantiate the notion that surface variability from higher latitudes may influence equatorial SST variability through the ``ocean tunnel''.
DE: 4203 Analytical modeling
DE: 4231 Equatorial oceanography
DE: 4508 Coriolis effects
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting