HR: 1400h
AN: A23A-10    [Abstracts]
TI: Simulation of a Coupled Mechanism for Local Intraseasonal Variability in the Tropics
AU: * Agudelo, P A
EM: pagudelo@eas.gatech.edu
AF: School of Eart and Atmospheric Sciences Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AU: Curry, J A
EM: curryja@eas.gatech.edu
AF: School of Eart and Atmospheric Sciences Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AU: Clayson, C A
EM: clayson@met.fsu.edu
AF: Department of Meteorology Florida State University, 404 Love Building/Meteorology, Tallahassee, FL 23064520, United States
AB: During the transition phase between suppressed and active phases of the tropical intraseasonal oscillation (ISO) the atmosphere and ocean undergo important changes. Positive SST anomalies cause changes in atmospheric boundary layer temperature creating anomalous surface pressure gradients, winds and low level mass convergence which may lead to convection. Surface winds are strengthened and exert stress over warmer than average surface oceanic waters, leading to enhanced evaporation, and low-level atmospheric moistening which preconditions the atmosphere for deep convection. The cloudiness associated with the active convection acts to cool the surface of the ocean. With the reduction of SST the active phase ends. This local oscillation will then project onto the zonal circulation resulting in the eastward propagation of the convective anomalies. According to the previous mechanism, the time needed to elevate the SST by enhanced downward solar radiation during the suppressed phase as well as the time needed to destabilize the lower troposphere due to the higher SST determines the local timescale of the ISO. This implies that dynamics of the oceanic mixed layer is also very important for the ISO timescale. In this study we explore the role of local ocean-atmosphere coupling in generating intraseasonal variability, and specifically, the role of the oceanic mixed layer dynamics in determining the time-scale of the resulting oscillation. In particular, we study the mechanism previously described by using two different one-dimensional coupled models. In both setups, the ocean component is the Kantha-Clayson ocean mixed layer. In the first case, the atmospheric component is an empirical scheme designed based on TOGA/COARE observations. In this scheme, the rate of change of different atmospheric variables such as surface wind, specific humidity, outgoing longwave radiation, among others are statistically related to changes in SST. In this manner, SST controls the atmosphere which then drives changes in SST, allowing the reproduction and detailed study of the observed coupling mechanism. In the second set-up, the atmospheric component of the couple system corresponds to the single column model version of the NCAR CCM. In this framework, the evolution of the transition period is studied under different ocean-atmosphere configurations to determine the degree of local coupling associated to ISO events.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3374 Tropical meteorology
DE: 4504 Air/sea interactions (0312, 3339)
DE: 4572 Upper ocean and mixed layer processes
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly