The response of the Pacific storm track and atmospheric circulation to Kuroshio Extension variability


An index of the Kuroshio Extension front strength is produced using a maximum covariance analysis between sea-surface temperature (SST) and sea-surface height (SSH) gradient observations, and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data (1992–2011). It is found that when the Kuroshio Extension is less (more) meandering, with a stronger (weaker) SST front, the atmospheric heat transport by transient eddies is increased in the western (eastern) Pacific region, consistent with an increase (decrease) in low-level baroclinicity. Analysis of the eddy–mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the Eastern Pacific, where blocking frequency is strongly influenced. The above relationships cannot be reconciled with the known response of the North Pacific storm track to remote forcing from the Tropical Pacific, nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds. Rather, the zonal shift in the storm track highlighted here, and the associated changes in the large-scale circulation, are interpreted as a response to the interannual variability of the Kuroshio Extension front.

Quarterly Journal of the Royal Meteorological Society