Numerical experiments of the storm track sensitivity to oceanic frontal strength within the Kuroshio/Oyashio Extensions

摘要

The sensitivity of the North Pacific storm track to midlatitude oceanic frontal strength within the Kuroshio/Oyashio Extensions is investigated by applying artificially changed meridional sea surface temperature (SST) gradients in the Weather Research Forecasting model version 3.4. The result of sensitivity experiments further confirms the close relationship between the storm track activity and meridional SST gradient; i.e., the storm track activity can be intensified as a response to increases in the oceanic frontal strength. In order to better understand the mechanism for the storm track intensification due to increased SST gradient, velocity-temperature correlation and local energetics are analyzed. The result indicates that the enhancement of the meridional SST gradient leads to amplitude magnification of eddy meridional velocity and temperature and their phase consistency, suggesting that synoptic-scale eddies tend to approach the optimum structure for the baroclinic energy conversion, which is mainly responsible for the SST front-induced enhancement of storm track activity. In order to estimate the impact of the oceanic front on the maintenance of the near-surface baroclinicity, further investigation is made by the composite analysis. With the increase in oceanic frontal strength, the near-surface baroclinicity experiences a slow but strong restoration. The increase in the meridional SST gradient results in the intensification in the cross-frontal differential sensible heat flux, which can more effectively offset the relaxing effect of the transient eddy poleward heat transport.