[AOS29-P01] Effects of Koshu Seamount on the Development of Baroclinic Instability Leading to the Kuroshio Large Meander
Keywords:Large Meander of the Kuroshio, Koshu Seamount, Baroclinic Instability, Topographically Trapped Wave, Two-Layer Quasi-Geostrophic Model, Linear Stability Analysis
In this study, the effects of Koshu Seamount on this rapid amplification leading to the LM path formation are revisited using a two-layer quasi-geostrophic model that takes into account the effect of bottom topography. Numerical experiments show that the transition processes from the NLM path to the LM path can be successfully reproduced only when the bottom topography mimicking Koshu Seamount is incorporated. In this case, the upper layer meander trough is rapidly amplified through baroclinic interaction with a lower layer anticyclone during their passage over the seamount. A linear stability analysis shows that baroclinic instability over a seamount can be caused by the coupling between the upper layer Rossby wave propagating eastward in the background flow and the lower layer topographically trapped wave propagating clockwise around the seamount. These two waves propagate in the same direction over the northern slope of the seamount so that they can resonantly interact with each other. The wavelength and the spatial structure of this unstable mode are close to those of the numerically reproduced small meander in the early stage of its rapid amplification over the seamount, showing that the baroclinic instability catalyzed by a seamount is an essential process in the formation of the LM path of the Kuroshio.