HR: 1300h
AN: OS52D-15    [PDF]
TI: Equatorial Waves and the 2002-2003 El Nino
AU: * Zhang, X
EM: xbzhang@ocean.washington.edu
AF: School of Oceanography University of Washington, Box 357940, Seattle, WA 98105 United States
AU: McPhaden, M J
EM: Michael.J.Mcphaden@noaa.gov
AF: NOAA/Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AB: A simple 4-vertical mode linear equatorial wave model, based on method of characteristics, is developed to simulate low frequency wave dynamics in the tropical Pacific for the recent 2002-2003 El Nino event. Wind forcing is via both ECMWF and Quikscat scatterometer wind stresses. Model parameters were tuned and outputs validated with TOPEX/Poseidon and Jason altimeter measurements. The onset of the 2002-2003 event coincided with several intraseasonal eastward propagating downwelling equatorial Kelvin waves forced by episodic westerly winds in early-to-mid 2002. Most notable of these downwelling Kelvin waves were those in May and June 2002 with sea level elevations of 5-10 cm. The El Nino then matured in the latter half of 2002 in response to almost continuous westerly wind anomalies in the western Pacific, during which sea level rose east of the date line by 10-20 cm. At the same time, the westerly wind anomalies forced westward upwelling Rossby waves which lowered sea level by 5-10 cm west of date line. On arrival at the western boundary, these upwelling Rossby waves reflected into eastward propagating upwelling Kelvin waves which resulted in a tendency for sea level to fall (and the thermocline to rise) along the equator in accordance with delayed oscillator theory. In addition, an even stronger shoaling tendency resulted from direct wind forcing by easterly anomalies in the western Pacific during the late 2002 and early 2003. These results will be compared with results for the 1997-98 El Nino using the same model. Implications for theories of ENSO variability will also be discussed.
DE: 4231 Equatorial oceanography
DE: 4255 Numerical modeling
DE: 4522 El Ni¤o
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting