Dipolar redistribution of summertime tropical cyclone genesis between the Philippine Sea and the northern South China Sea and its possible mechanisms

Recent observational records show that the dipole oscillation between the Philippine Sea (PS) and the northern South China Sea (nSCS) is a leading empirical orthogonal function (EOF) of summertime tropical cyclone (TC) genesis in the western North Pacific (WNP). This PS‐nSCS oscillation is characterized by a distinguished decadal variability in addition to an interannual variability. Meanwhile, the typical El Niño–Southern Oscillation (ENSO)‐related mode is found in the second EOF mode, which is predominantly interannual. With regard to the PS‐nSCS oscillation, its interannual component appears to be linked with the previous wintertime ENSO event, but the linkage is not so robust in the sense that about half of its significant events are classified as the ENSO‐related case, whereas its decadal component is coupled to a sea surface temperature anomaly (SSTA) in the central Pacific with its equatorial core near the Niño‐4 region, which is flanked by an opposite SSTA on both sides along the latitudinal belt. Interestingly, this SSTA pattern resembles that related to the ENSO Modoki, and equivalently, the transitional phase of ENSO. The ENSO Modoki is regionally manifested by the anomalous zonal SST gradient between the equatorial western and central Pacific; thus the decadal modulation of this anomalous zonal SST gradient can be regarded as an actual forcing that forms and modulates the decadal PS‐nSCS oscillation. In addition, the decadal PS‐nSCS oscillation is compared with the decadal basin‐wide TC genesis variation in terms of the Pacific SSTA pattern and the associated anomalous large‐scale environments.