HR: 10:50h
AN: OS31D-03    [PDF]
TI: The Influence of Multiplicative Stochastic Forcing on a Coupled Ocean-Atmosphere Model of the El Ni\~{n}o-Southern Oscillation
AU: * Perez, C L
EM: cristina@iri.columbia.edu
AF: Department of Applied Physics and Applied Mathematics, Columbia University, 202 Monell Building P.O. Box 1000, Palisades, NY 10964-8000 United States
AU: Moore, A M
EM: andy@bondi.colorado.edu
AF: Program in the Atmospheric and Oceanic Sciences, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, PAOS UCB 311 University of Colorado, Boulder, CO 80309-0311 United States
AU: Zavala-Garay, J
EM: javier@orca.rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, Univeristy of Miami, 4600 Richenbacker Causeway, Miami, FL 33149-1031 United States
AU: Kleeman, R
EM: kleeman@cims.nyu.edu
AF: Courant Institute of Mathematical Sciences, New York University, Room 901 251 Mercer Street, New York, NY 10012 United States
AB: The El Ni\~{n}o-Southern Oscillation (ENSO), while exhibiting variability on interannual to decadal timescales, interacts with atmospheric phenomena which have lifetimes of weeks to months. Many observational studies have suggested that the intraseasonal Madden-Julian Oscillation (MJO) may play an important role in regulating the development of El Ni\~{n}o events. It is known that the MJO couples intermittently to the ocean through the deep convection which accompanies it over the western to central Pacific which leads to the possibility that ENSO may be responding to multiplicative stochastic forcing by the MJO. ``Multiplicative'' means that the stochastic forcing depends on a function of the current state of the model (e.g. Ni\~n{o} 3 index) whereas an ``additive'' forcing does not and is thereby is uncorrelated with the deterministic part of the model. Diverse model studies already support the idea that the tropical Pacific is an inherently stable system and ENSO variability is maintained by additive stochastic atmospheric forcing. We derive stochastic forcing from observations of surface wind and SST which we apply to an intermediate coupled model of ENSO in both multiplicative and additive scenarios. Our experiments show that the ENSO model's underlying probability distribution function (PDF) changes significantly depending on the nature of forcing in conjunction with the stability of the model. We compare time series of the model Ni\~{n}o 3 index for various forcing experiments to the observed 51-year record of the monthly Ni\~{n}o 3 index and find that it is a strong possibility that multiplicative stochastic forcing, and by extension the MJO, plays an important role in creating the observed ENSO variability.
DE: 4203 Analytical modeling
DE: 4215 Climate and interannual variability (3309)
DE: 4263 Ocean prediction
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting