HR: 13:55h
AN: A33B-02    [Abstracts]
TI: Mechanisms for Lagged Atmospheric Response to ENSO SST Forcing
AU: * Su, H
EM: hui@atmos.ucla.edu
AF: University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095
AU: Neelin, J D
EM: neelin@atmos.ucla.edu
AF: University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095
AU: Meyerson, J E
EM: hobo@atmos.ucla.edu
AF: University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095
AB: The sensitivity and mechanism for the lagged response of tropical tropospheric temperature to El Ni\~no SST forcing are examined using results from the quasi-equilibrium tropical circulation model (QTCM) coupled to a slab mixed-layer ocean model. It is found that the lag and amplitude of tropospheric temperature response depend on mixed-layer ocean depth, ENSO SST forcing period and areal fraction of mixed-layer ocean region. The phase lag is not a monotonic function of mixed-layer depth. It maximizes at moderate MLD and increases with SST forcing period. The amplitude decreases with MLD and increases with SST forcing period. The amplitude and phase lag of tropospheric temperature response seem to be insensitive to the seasonal cycle of SST. While ENSO region convective heating (precipitation) anomalies, are closely tied to SST anomalies, the tropical mean precipitation seems best viewed as a complex by-product of the response rather than as a driver. One useful parameter determining the lag of tropospheric temperature to ENSO SST is the free decay time scale of the coupled system. This parameter combines effects of top-of-atmosphere fluxes, surface flux exchanges, tropics-midlatitude moist static energy transports and mixed-layer ocean heat capacity. It is indicative of the extent to which the lagged response of tropical tropospheric temperature to ENSO SST is a coupled phenomenon.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4215 Climate and interannual variability (3309)
DE: 4522 El Ni¤o
DE: 1854 Precipitation (3354)
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting