Impacts of the subarctic frontal zone on the North Pacific storm track in the cold season: an observational study

In this study, potential impacts of the North Pacific subarctic frontal zone (SAFZ) variation, including its intensity variation and meridional shift, upon the subseasonally varying North Pacific storm track are investigated by using the 100-year reanalysis data sets. Regression analysis indicates that the changes in the SAFZ intensity and meridional position have significant influence on the North Pacific storm track, which intensifies with the strengthening of the SAFZ and moves northwards following the northwards shift of the SAFZ. However, the storm-track response pattern exhibits distinct differences from one calendar month to another. Specifically, the storm-track response to the SAFZ intensity variation is strongest in February and March; while its response to the SAFZ meridional shift is most pronounced in November and December. However, the storm-track response is relatively weak in January. Further analysis shows that the intensified (or northwards shifted) SAFZ would result in changes in the near-surface baroclinicity and hence affects the storm track, while the weak storm-track response in January is not the result of the anomalous near-surface baroclinicity. The investigation of the local energetics reveals that changes in the baroclinic energy conversion (BCEC) associated with the SAFZ variation are consistent with the storm-track anomalies, indicating that the BCEC plays a crucial role in modulating the subseasonal changes in the storm-track response. In January, the weakened BCEC contributes to the reduced storm-track response to the SAFZ variation.