HR: 0830h
AN: A31C-0043    [PDF]
TI: Seasonal Dependency of Diurnal and Semidiurnal Surface Wind Variations Over the Tropical Pacific Ocean
AU: * Ueyama, R
EM: ru22@cornell.edu
AF: National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80305
AB: To advance our understanding of the behavior of the large-scale atmospheric circulation, the daily cycle of the near-surface wind field over the tropical Pacific Ocean was examined. Hourly wind measurements collected from 53 moored buoys in the Tropical Atmosphere Ocean array ($9\deg$N-$8\deg$S, $165\deg$E-$180\deg$W) from 1993 through 2002 were used to document seasonal changes of the diurnal and semidiurnal harmonics of surface wind variability. The zonal wind component was dominated by a semidiurnal variation, with a near-uniform amplitude ($\sim$0.14 m/s) and phase ($\sim$0300 and 1500 local time) across the tropical Pacific. The semidiurnal cycle showed no apparent seasonal differences and was generally well explained by atmospheric thermal tidal theory. The meridional wind component, on the other hand, exhibited primarily diurnal variability (amplitudes $\sim$0.17 m/s) with opposite phase on either side of the equator, particularly in the western Pacific ($\sim$0600-0900 local time in the Northern Hemisphere, 1800-2100 local time in the Southern Hemisphere). This induced a diurnal cycle of wind divergence near the equator, with enhanced convergence in the late evening. This diurnal cycle of surface wind divergence may contribute to the diurnal cycle in convection and rainfall observed near the equator. Some seasonal dependence was found in the diurnal meridional wind variations in the eastern equatorial Pacific, with stronger amplitudes during boreal summer and autumn.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting