DATE2025.11.03 #Awards & Prizes

Professor Emeritus Toshiyuki Hibiya has been awarded the Medal with Purple Ribbon in the autumn of 2025.

Professor Emeritus　Toshiyuki Hibiya

Professor Emeritus Toshiyuki Hibiya has been awarded the Medal with Purple Ribbon in the autumn of 2025. Professor Hibiya retired from the Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, in 2022 and currently serves as a Visiting Professor at Tokyo University of Marine Science and Technology, as well as an Advisor to the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).

Professor Hibiya has made pioneering contributions to our understanding of turbulent mixing in the deep ocean, a fundamental process that governs the upwelling of deep water through the transport of heat (buoyancy) from the surface down to the deep layers, thereby influencing the meridional overturning circulation and long-term climate variability.

Through highly precise numerical experiments, he theoretically elucidated how internal tides — generated by the interaction of tidal currents with ocean ridges and seamounts — can trigger turbulent mixing via latitude-dependent parametric resonance, which excites high-wavenumber, near-inertial shear flows. He then verified the latitudinal dependence of turbulent mixing intensity through in situ microstructure observations, producing the world’s first global map of turbulent mixing intensity in the mid- and deep layers. Furthermore, Professor Hibiya demonstrated that atmospheric disturbances — long considered, along with tides, as an energy source of turbulent mixing — have a negligible effect on turbulent mixing in the mid- and deep layers. Instead, he proposed that “tall mixing hotspots”, resulting from the breaking of internal lee waves generated by strong tidal flows over rough seafloor topography, may hold the key to resolving the long-standing “missing mixing problem” in physical oceanography. Building on these achievements, he developed new parameterizations of turbulent mixing in the mid- and deep layers, as well as bottom layers, thereby enabling the improvement of the prediction accuracy of global ocean and climate models from a microscale perspective.

In recognition of his outstanding scientific accomplishments, Professor Hibiya has received numerous honors, including the Okada Prize of the Oceanographic Society of Japan (1989), the Society Prize of the Oceanographic Society of Japan (2008), the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology, Award for Science and Technology (2020), the Prime Minister’s Commendation for Merits in Promoting a Maritime Nation (2021), his election as a Fellow of the International Union of Geodesy and Geophysics (IUGG, 2023), and a Fellow of the Japan Geoscience Union (JpGU, 2025).

We extend our heartfelt congratulations to Professor Hibiya on this prestigious award and wish him continued health and success in all his endeavors.

Medal of Honor Medal with Purple Ribbon in Autumn 2025

(Written by: Professor Yukio Masumoto, Department of Earth and Planetary Science)