Bottom pressure variability in the Kuroshio Extension driven by the atmosphere and ocean instabilities

Abstract

The relative importance of atmospheric forcing on oceanic intraseasonal (7-60 days) barotropic variability is investigated in the Kuroshio Extension region by comparing in situ measurements with two models: a wind-forced barotropic model and an ocean general circulation model. Large-scale wind stress curl forcing (an atmospheric mode) becomes successively more influential with decreasing periods (at 7-15 day band, compared to 15-30 day and 30-60 day bands). On the other hand, oceanic instabilities (an oceanic mode) become more important with increasing period (at 30-60 day band, compared to 15-30 day and 7-15 day bands). Comparison between the barotropic model and the ocean general circulation model results reveals differences on the broader gyre scale: the atmospheric mode exhibits basin-mode-like spatial patterns with faster phase propagation from east to west, whereas the oceanic mode shows eddy-like spatial patterns with slower westward propagation. The atmospheric mode, which has received less attention on the intraseasonal time scale, contributes an important fraction to the barotropic variability in the Kuroshio Extension region.