HR: 11:30h
AN: A52B-08    [Abstracts]
TI: Oscillations of the Intertropical Convergence Zone and the Genesis of Easterly Waves
AU: * Toma, V E
EM: violeta.toma@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AU: Webster, P J
EM: pjw@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0340, United States
AB: It is noted that in regions of strong cross-equatorial pressure gradient (CEPG), the climatological Intertropical Convergence Zone (ITCZ) is more intense than in regions where the CEPG is smaller. In the eastern tropical Pacific, where the CEPG during the northern summer is set up by the slowly varying SST gradient across the equator, there is a mean advection of anticyclonic vorticity across the equator denoting broad regions of inertial instability. Furthermore, in such regions, the maximum convection and convergence is located equatorward of the maximum sea-surface temperature and the minimum sea level pressure. Using a combination of diagnostic and modeling studies it is shown that the location of the mean convection is determined by the magnitude of the CEPG (which determines the magnitude of the divergent meridional wind field) and where the advection of absolute vorticity is matched by the vortex stretching term in the absolute vorticity equation. The ITCZ is shown to be highly transient with strong oscillations occurring in the 3-8 day period range. A series of modeling experiments using the Weather Research and Forecast Model (WRF) are performed to show that the observed transients arise from a continual state of inertial instability in which the ITCZ regime is continually destabilized and stabilized against a background large-scale destabilizing CEPG. The model response to the variations of SST and SST gradient is tested. Significant SST gradients which result in stronger pressure gradients generate greater advection of negative absolute vorticity across the equator, with enhancement of convection, north of the zero absolute vorticity line.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting