[A-CG36] Extratropical oceans and atmosphere

[ACG36-P19] Change in the atmospheric forcing increases wintertime sea surface temperature in the subpolar region around Japan

*Gaku Nishihira¹, Shusaku Sugimoto^1,2 (1.Graduate School of Science, Tohoku University, 2.Advanced Institute for Marine Ecosystem Change, Tohoku University)

Keywords:SST trend, Subarctic front, Japan Sea

We investigated long-term SST changes in mid-latitude North Pacific in winter (January–March) using satellite-derived data and in-situ temperature/salinity profiles. We found that SST has increased remarkably after 1982 around the subarctic front (SAF) region, which reached +3.0 °C per century. Remarkable SST warming trends are also observed in the Japan Sea, with zonal band structures (e.g., Matsuura and Kida, 2024). In the last JpGU2024, we pointed out that the SST increase around the SAF region might reflect a decrease in the inflow of cold air with the weakening of the Aleutian Low and warm water transport due to the northward shift of the Kuroshio Extension.
To evaluate the relative roles of the change in atmospheric forcing and the ocean advection quantitively for increasing SST around Japan, we conducted a heat budget analysis, integrated over the surface ocean layer by using oceanic reanalysis data. We treat net heat flux as one of the forcing terms and introduce a damping term, and compare the solution of integral in space along mean streamlines from upstream boundary conditions with the observational data. As a result, we found that the change in atmospheric forcing could reconstruct the SST increase in the SAF region and the Japan Sea, while the northward shift of streamline is considered in the Kuroshio Extension region. This result indicates that change in the pathway of cold-air outbreaks from the large continent influences inter-basin surface ocean temperature over the subpolar region.