An observational study of the North Pacific storm-track impact on the midlatitude oceanic front

摘要

A lagged Maximum Covariance Analysis is used to examine the impact of North Pacific storm-track activity on midlatitude oceanic frontal intensity in this study. It is found that an enhanced storm track tends to intensify the oceanic frontal intensity with a lag of 1-2 months. The forcing effect of storm-track anomalies on oceanic frontal intensity is strongest in autumn, followed by that in summer and winter, and it is weakest in spring. Moreover, the mixed layer heat budget analysis suggests that sea surface temperature anomalies (SSTAs) related to oceanic fronts are primarily attributed to the storm-track-induced net surface heat flux and Ekman advection anomalies, while contributions of geostrophic advection and entrainment are relatively small. In summer and autumn, the impact of net surface heat flux anomalies on SSTAs plays a more important role than that of Ekman heat transport anomalies. Whereas in winter, Ekman heat transport anomaly forcing is comparable to the net surface heat flux forcing. Anomalous turbulent heat fluxes contribute to generating net surface heat flux anomalies in those three seasons, while the shortwave radiative fluxes make a strong contribution in summer but have little impact in winter. The anomalies of both net surface heat flux and Ekman heat transport are presumed to be associated with storm-track-induced surface wind anomalies. Results of the present study provide observational evidences for the positive feedback between the North Pacific storm-track activity and midlatitude oceanic frontal intensity.