[A-CG43] Kuroshio Large Meander

[ACG43-01] Subtropical Mode Water south of Japan impacts typhoon intensity

★Invited Papers

*Eitarou Oka¹, Shusaku Sugimoto², Fumiaki Kobashi³, Hatsumi Nishikawa¹, Sachie Kanada⁴, Tomoe Nasuno⁵, Ryuichi Kawamura⁶, Masami Nonaka⁵ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Graduate School of Science, Tohoku University, 3.Department of Maritime Systems Engineering, Tokyo University of Marine Science and Technology, 4.Institute for Space-Earth Environmental Research, Nagoya University, 5.Japan Agency for Marine-Earth Science and Technology, 6.Faculty of Science, Kyushu University)

Keywords:Subtropical Mode Water, typhoon, Kuroshio large meander, decadal variability

Subtropical Mode Water (STMW) is a vertically uniform layer found within the upper permanent thermocline in the western subtropical gyre of the world oceans. By using Argo profiling float data, we demonstrate that STMW south of Japan, whose thickness varies decadally, modulates the overlying thermal structure throughout the year by increasing isotherm uplift with increasing thickness, particularly in the warm seasons when the seasonal thermocline is present. Since 2015, the STMW south of Japan has thinned by ~100 m due to the occurrence of the Kuroshio large meander and has increased the temperature in the overlying layers by up to ~1ºC, suggesting that its decadally varying thickness affects the typhoon intensity south of Japan. In fact, 50-year observations show that the tropical cyclone intensification rate has been significantly reduced in years with thicker STMW and enhanced in years with thinner STMW. Moreover, numerical simulation for Typhoon Hagibis (2019), which caused widespread damage to eastern Japan, demonstrates that its minimum central pressure would increase by up to 6.5 ± 1.2 hPa if the STMW south of Japan had a thickness equivalent to what it was in 2015 when it was at its peak. The recently suggested STMW decline in a warming climate thus warns of the future acceleration of ocean surface warming and typhoon intensification.