| Two aspects of the Kuroshio Extension (KE) relevant to the North Pacific climate variability---its low-frequency variability and influence on the atmosphere---are studied using a hierarchy of numerical models with various complexity and observations. Both idealized regional Ocean General Circulation Model (OGCM) experiments and analysis of a multi-decadal high-resolution global OGCM hindcast suggest that the low-frequency variability of oceanic dynamical fields in the Western North Pacific is highly concentrated near the KE front.; Much of the low-frequency variability of the sea surface height (SSH) field in the KE region is explained by two meridional modes that are trapped by the KE front. The first mode represents a north-south shift and an associated speed change of the KE jet with its time evolution related to the 1976/77 climate regime shift, a response also found in the regional OGCM experiments. Both the spatial structure and time series of the first mode simulated by the OGCM is in close agreement with satellite altimeter and XBT observation. On the other hand, the second mode reflects intensity variation of the jet with a quasi-regular 10-15 year period.; The spatial structure of these modes is in distinct contrast with that of the linear Rossby wave or Sverdrup adjustment but their time series are well predicted by the linear Rossby wave theory. We separate SSH variability into meridional low-pass and high-pass components, and the former agrees quite well with the linear model simulation. On top of the large scale structure, the modes exhibit fine structure involving variation of recirculation and inertial jet, part of which is contributed by oceanic intrinsic dynamics. Despite the clearly separated spatial structure, both the large-scale and the frontal-scale variations share nearly identical time evolution, suggestive of the wind-forced Rossby waves triggering the frontal variation that inherently has its own spatial and temporal scales.; Regional atmospheric model experiments reveal that the SST anomalies associated with the KE front could give rise to changes, which closely follow the frontal SST anomalies, in surface wind, sea level pressure and column-integrated liquid water that is induced by the surface convergence of the vector winds onto the front. |
