HR: 0830h
AN: OS41B-0803    [PDF]
TI: Fast and slow ENSO modes
AU: * An, S
EM: sian@hawaii.edu
AF: International Pacific Research Center, Univ. of Hawaii, 1680 East West Rd., POST 401, Honolulu, HI 96822 United States
AU: Jin, F
EM: jff@soest.hawaii.edu
AF: Dept. of Meteorology, Univ. of Hawaii, 2525 Correa Rd., Honolulu, HI 96822 United States
AB: Climate variability in the tropical Pacific has a rich frequency spectrum that partly results from coupled modes with different time scales. We examined the contributions of the thermocline feedback (the vertical advection of anomalous subsurface temperature by the mean upwelling) and zonal advective feedback (the zonal advection of mean sea surface temperature by anomalous current) in determining the time scales of the coupled modes. Firstly, using a dynamical ocean model, we study the dependence of maximum amplitudes and locations of equatorial zonal current and thermocline on the time scales of the wind forcing. Then we examine in a linearized intermediate air-sea coupled model the impacts of these feedbacks on the co-existence of leading coupled modes of different time scales. For slowly varying wind forcing, amplitudes of zonal currents are very weak and locate at western Pacific, whereas the thermocline response is strong. The zonal advective feedback thus tends but to be of secondly importance in a slow mode of interannual periodicity although it plays a dominating role in a fast coupled mode of near annual periodicity. The changes in the basic state of the coupled system can have significant impacts on the relative importance of the two main feedbacks and thus the periodicity and stability of the leading modes the coupled tropical Pacific climate system.
DE: 3309 Climatology (1620)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4504 Air/sea interactions (0312)
DE: 4522 El Ni¤o
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting