[A-CG49] Kuroshio Large Meander

[ACG49-P02] Wintertime atmospheric response to extreme northward Kuroshio Extension meandering

*Kenji Aono¹, Shusaku Sugimoto², Atsushi Okazaki³ (1.Center for Environmental Remote Sensing, Chiba University, 2.Department of Geophysics, Graduate School of Science, Tohoku University, 3.Institute for Advanced Academic Research, Chiba University)

Keywords:Marine Heatwave, Kuroshio Extension, Kuroshio Large Meander, WRF

Since the spring of 2023, the Kuroshio Extension (KE) has meandered northward extremely, reaching a region off the coast of Iwate and Aomori prefectures. This has caused exceptionally high sea surface temperature (SST), i.e., a formation of a marine heatwave (MHW), off the Sanriku coast. Over this area, cold-dry northwesterly monsoonal winds blow from the Eurasian continent in winter and a large amount of heat is released from the ocean to the atmosphere, which may affect large-scale atmospheric circulation. To investigate the atmospheric response to the high SST off the Sanriku coast in the winter of 2024, we conducted numerical experiments using WRF. Here, we conducted two types of experiments: an experiment in which the SST in winter 2024 was forced, and an experiment in which the SST off the Sanriku coast was replaced with a value before 2023. In other words, we conducted a sensitivity experiment to the presence or absence of MHW off the Sanriku coast. We used the ERA5 ensemble data (10 members) as the initial and boundary conditions of the atmosphere. The numerical experiment was for January 2024 with a horizontal resolution of 0.5 degree, covering an area from 3.5S to 79.5N, and 0E to 360E. The results of the sensitivity experiment indicated that the momentum vertical mixing mechanism associated with the high SST strengthened the westerly winds off the Sanriku coast. Then, the surface winds converged on the eastern side of the high SST region off the Sanriku coast, which corresponds to the downwind side, and precipitation increased. These results suggest the impact of the MHW off the Sanriku coast on the free atmosphere. In the presentation, we would like to discuss the impact of the MHW on large-scale circulation.