Impact of Tropical Cyclones on Geostrophic Velocity of the Western Boundary Current.

Tropical cyclones (TC), which are among the most destructive natural phenomena on Earth, have significant impacts on the western boundary current (WBC). We quantify the direct impact of TCs on the surface geostrophic velocity of the Kuroshio, the WBC in the western North Pacific, by analyzing satellite‐derived geostrophic current data and using results from theoretical and numerical models. The study reveals that TCs decrease the surface geostrophic velocity by 14 cm s−1 which is 16% of the mean velocity of the Kuroshio (85 cm s−1), with the reduced velocity maintained for a month. The decrease in velocity of the Kuroshio is mainly (87%) due to the effect of TC‐driven upwelling ("Cooling effect"), the effect of ocean heat uptake after the TC ("Warming effect") being minor (13%); these are basically enabled by the strong thermal gradient around the Kuroshio. Plain Language Summary: The tropical cyclone (TC), also known as hurricane or typhoon, has a strong impact on the ocean as well as the land. In this study, we investigate how TCs affect ocean currents, with special focus on the Kuroshio, the western boundary current (WBC) in the North Pacific region. By analyzing satellite‐derived data, and building theoretical and numerical models, we deduce that when a TC hits the Kuroshio, its surface velocity decreases by 16%. This work makes a significant contribution by providing a quantitative understanding of the influence of TCs on the WBC. Further, given that the WBC is the strongest ocean current system on Earth and plays a key role in maintaining global heat balance, this study emphasizes the potential importance of the TC‐induced change on the current for the global distribution of heat energy. Key Points: Tropical cyclones (TC) decrease the surface geostrophic velocity of the Kuroshio by 14 cm s−1 (16% of the mean velocity)"Cooling Effect" of the TC‐driven upwelling explains 87% of the geostrophic velocity decrease immediately after a TC"Warming Effect" of the ocean heat uptake explains 13% of the geostrophic velocity decrease, which is maintained for ∼30 days after a TC [ABSTRACT FROM AUTHOR]