Seasonal-to-Interannual Variations and Modulation Mechanisms in the Kuroshio Leaking Path in the Luzon Strait

The Kuroshio Leaking path is one of the most common paths of Kuroshio in the Luzon Strait. It can trap huge amount of Kuroshio water intruding into the South China Sea (SCS) and have a significant impact on the temperature and salinity balance, circulation, mesoscale eddies, and biogeochemical processes in the SCS. Therefore, it is of great significance to carry out the research on the Kuroshio Leaking path. In this study, different Kuroshio intrusion paths are systematically identified based on the sea surface characteristics using satellite altimeter data from 1993 to 2020. The seasonal and interannual variations and their modulation mechanisms of the Leaking path are investigated in detail. The results show that the occurrence probability of Kuroshio Leaking intrusion path exceeds 40.1% and exhibits a double-peak seasonal variation. It is stronger in the boreal winter half-year (October to April of the next year), and gets strongest in March and October, with the occurrence probabilities of 73.4% and 58.3%, respectively. The development of the northeast wind in the boreal winter half-year and the weaker upstream Kuroshio strength are beneficial to the Kuroshio intrusion into the SCS, but the northeast monsoon in winter is more conducive to the generation of Kuroshio Looping intrusion path, which reduces the occurrence probability of the Leaking path. Thus, the Leaking path shows a double-peak seasonal variation. On the interannual scale, the Leaking path has a significant correspondence with the Pacific Decadal Oscillation (PDO), stronger in the positive PDO phases and weaker in the negative PDO phases, mainly modulated by the coastal Kelvin waves and the upstream Kuroshio strength. During the positive phases of the PDO, the negative sea surface height anomaly signal in the Northwest Pacific propagates to the western Luzon Island region in the form of coastal Kelvin waves, increasing the meridional pressure gradient across the Luzon Strait, thereby promoting the development of the Leaking path. At the same time, the weaker upstream Kuroshio strength is also beneficial to the formation of the Kuroshio Leaking path. Further analysis shows that the Leaking path contributes to 70% and 54.4% of the volume transports at the sea surface and in the upper 500 m through the Luzon Strait, respectively, indicating the significant contribution and mudulation effect of the Leaking path on the Luzon Strait volume transport.