Articles | Volume 19, issue 5
Nonlin. Processes Geophys., 19, 479–499, 2012
Nonlin. Processes Geophys., 19, 479–499, 2012

Research article 06 Sep 2012

Research article | 06 Sep 2012

Multiple equilibria and oscillatory modes in a mid-latitude ocean-forced atmospheric model

B. Deremble1, E. Simonnet2, and M. Ghil3,4 B. Deremble et al.
  • 1Florida State University, 117 N. Woodward Ave., Tallahassee, FL 32306-4320, USA
  • 2Institut Non Linéaire de Nice (CNRS and UNSA), Valbonne, France
  • 3Environmental Research and Teaching Institute (CRES-ERTI) and Laboratoire de Météorologie Dynamique (CNRS and IPSL), Ecole Normale Supérieure, Paris, France
  • 4Department of Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, USA

Abstract. Atmospheric response to a mid-latitude sea surface temperature (SST) front is studied, while emphasizing low-frequency modes induced by the presence of such a front. An idealized atmospheric quasi-geostrophic (QG) model is forced by the SST field of an idealized oceanic QG model. First, the equilibria of the oceanic model and the associated SST fronts are computed. Next, these equilibria are used to force the atmospheric model and compute its equilibria when varying the strength of the oceanic forcing.

Low-frequency modes of atmospheric variability are identified and associated with successive Hopf bifurcations. The origin of these Hopf bifurcations is studied in detail, and connected to barotropic instability. Finally, a link is established between the model's time integrations and the previously obtained equilibria.