HR: 16:45h
AN: OS52K-10    [PDF]
TI: A delayed action oscillator shared by QBO and QDO signals in the Indian Ocean
AU: * White, W B
EM: wbwhite@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0230 United States
AU: Tourre, Y M
EM: tourre@medias.cnes.fr
AF: Lamont Doherty Earth Observatory, Columbia University, Rt. 9W, Palisades, NY 10964 United States
AB: The quasi-biennial oscillation (QBO) near 2.5 year period and quasi-decadal oscillation (QDO) near 10-year period are observed in the Indian Ocean sharing similar patterns and evolution of covarying sea level height (SLH), sea surface temperature (SST), zonal surface wind (ZSW), meridional surface wind (MSW), and wind stress curl (WSC) anomalies. Similar SST variability occurs in the western equatorial and eastern tropical Indian Ocean for both QBO and QDO signals. Each signal has SLH, SST, and ZSW variability propagating slowly eastward along the equator and the west coast of Indonesia. These equatorial coupled waves generate off-equatorial coupled Rossby waves at the eastern boundary that propagate westward in covarying SLH, SST, and MSW variability at phase speeds 1/2-1/3 those of uncoupled Rossby waves. The coupled Rossby waves in the QBO signal near 10$\deg$ latitude are intensified by equatorial ZSW-induced WSC variability in the western ocean, whilst those in the QDO signal near 18$\deg$ latitude intensify intrinsically across the western ocean. Near the western boundary, these coupled Rossby waves excite equatorial coupled waves propagating eastward at speeds comparable to Rossby wave speeds, producing a delayed negative feedback to eastern equatorial SST variability. Together, equatorial and off-equatorial coupled waves form a delayed action oscillator (DAO) that maintains both signals against dissipation, as in the Pacific Ocean. The QBO signal produces warm (cool) SST anomalies in the western (eastern) equatorial Indian Ocean during 1995, 1998, and 2003 El Ni¤o's in the absence of any direct connection to El Ni¤o. We construct a DAO model, demonstrating how the various processes and delays yield delayed negative feedbacks that maintain both signals against dissipation at the observed frequencies of the 2 signals.
DE: 4504 Air/sea interactions (0312)
DE: 4522 El Ni¤o
DE: 4556 Sea level variations
DE: 4576 Western boundary currents
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting