Instability and Long-Term Variability of Strong Eastward Jet in an Oceanic Double-Gyre

Reynolds number (Re) dependency on the state of the oceanic double-gyre is investigated using a quasi-geostrophic model under constant forcing. The results are classified by energy level and length of the strong eastward jet. Both the energy levels and the lengths of the jet increase with an increase in Re until Re = 209, but begin to decrease at Re = 314. For Re = 209, intense eddy shedding occurs from the easternmost tip of the jet. For Re = 314, the jet is collapsed and eddy shedding occurs not only from the easternmost tip of the jet but also in the path of the jet. The realistic phenomena are considered to correspond to the results for Re = 314 in this study. The dominant instability in the long-term variability of the oceanic double-gyre seems to be different from the instability of the G-mode suggested by Simonnet and is related to shear instability.