A Modeling Study of the Intrinsic Variability of the Gulf-Stream and Kuroshio Extension Systems

University Of California-Irvine, Irvine CA

Investigators

Abstract

0221516 Primeau The purpose of this project is to test the hypothesis that the observed variability is a manifestation of intrinsic variability associated with the transitions between multiple equilibria. To do this the investigators will apply the recently developed methods of numerical bifurcation analysis to a hierarchy of ocean models with increasing realism to compute the solution branches found in the simpler model. The following clear criteria will be tested. If they are not met, the hypothesis must be rejected. 1. The equilibria with elongated recirculation gyres should be relatively less unstable than the equilibria with elongated gyres to be consistent with the observation that eddy activity decreases during periods of elongated gyres 2. The unstable modes associated with elongated recirculation gyres should have amplitude patterns that dominate in the downstream region of the jet, and those for the contracted recirculation gyres should have amplitude patterns that dominate in the upstream region, to be consistent with the observation that the eddy variability moves downstream during elongated states. 3. The mean zonal path of the jet extension should be further north for equilibria with elongated recirculation gyres to be consistent with the observation that the zonal mean path of the Gulf Stream and Kuroshio Extension moves northward during elongated states. Through this study a Ph.D. student will be trained in ocean modeling and in the application of dynamical systems theory to climate problems. In addition a software package to do numerical bifurcation analysis of ocean models will be produced and made available to the community. The possibility that the observed large-scale patterns of low-frequency variability are the result of intrinsic variability is an exciting one because observations show that these current changes are signi?cant contributors to the maintenance sea surface temperature anomalies and thus could contribute to mid-latitude climate variability.