HR: 11:05h
AN: OS52B-04    [Abstracts]
TI: Stochastic Forcing of the North Atlantic Wind-Driven Ocean Circulation
AU: * Chhak, K C
EM: chhak@colorado.edu
AF: Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Campus Box 3111, Boulder, CO 80309-0311 United States
AU: Moore, A M
EM: andy@bondi.colorado.edu
AF: Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Campus Box 3111, Boulder, CO 80309-0311 United States
AU: Milliff, R F
EM: milliff@cora.nwra.com
AF: Colorado Research Associates, 3380 Mitchell Lane, Boulder, CO 80301 United States
AU: Branstator, G
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Holland, W R
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 United States
AU: Fisher, M
AF: European Centre for Medium Range Weather Forecasts, Shinfield Park, Reading, RG2 9AX United Kingdom
AB: At midlatitudes, the magnitude of stochastic wind stress forcing due to atmospheric weather is comparable to that associated with the seasonal cycle. Stochastic forcing is therefore likely to have a significant influence on the ocean circulation. In this work, we examine the influence of the stochastic component of the wind stress forcing on the large-scale, wind-driven circulation of the North Atlantic Ocean. To this end a quasi-geostrophic model of the North Atlantic was forced with estimates of the stochastic component of wind stress curl obtained from the NCAR Community Climate Model. Analysis reveals that much of the stochastically-induced variability in the ocean circulation occurs in the vicinity of the western boundary and some major bathymetric features. Using the ideas of generalized stability theory (GST), we find that the patterns of wind stress curl that are most effective for inducing variability in the model have their largest projection on the most nonnormal eigenmodes of the system. These eigenmodes are confined primarily to the western boundary region and are composed of long Rossby wave packets that are Doppler shifted by the Gulf Stream to have eastward group velocity. Linear interference of these eigenmodes yields transient growth of stochastically-induced perturbations, and it is this process that maintains the variance of the stochastically-induced circulations. By examining the model pseudospectra, we find that the nonnormal nature of the system enhances the transient growth of perturbation enstrophy and therefore elevates and also maintains the variance of the stochastically-induced circulations in the aforementioned regions.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4263 Ocean prediction
DE: 4504 Air/sea interactions (0312)
DE: 4599 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting