Researcher Information

SASAKI Yoshi Nori

Associate Professor

Understanding the role of oceans in the climate system

Department of Earth and Planetary Sciences, Earth and Planetary Dynamics


Understanding interannual to continual variability of ocean circulation from theoretical, numerical, and statistical approaches
Understanding climate and environmental changes accompanied by oceanic variability

FieldPhysical oceanography, Meteorology, Climate
KeywordOcean circulation, Western boundary current, Air-sea interection, Sea level rise, Climate variability, Global warming, Ocean deoxygenation

Introduction of Research

I study oceanic variability and the associated climate and environmental changes using various approaches, that is, theory, numerical simulation, and statistical analyses.
I particularly examine ocean circulation variability in the mid-latitude. The Gulf Stream in the North Atlantic and the Kuroshio Extension in the North Pacific are one of the strongest western boundary currents in the world. The position and strength of these currents vary on interannual to decadal timescales, and affect atmospheric circulation and marine ecosystem. To explain these fluctuations, I propose a jet-trapped Rossby wave (Sasaki and Schneider 2011ab, Sasaki et al. 2013). This theory can account for the westward propagation signals in the North Pacific and the decadal variability of the Kuroshio Extension (Fig. 1). Except for these studies, I also examine temperature (Fig. 2) and salinity (Fig. 3) variability associated with ocean circulation changes.
Air-sea interaction in the mid-latitude has been attracted much attention in recent years. The warm western boundary currents, such as the Gulf Stream and the Kuroshio, form the sharp horizontal gradient of sea surface temperature (i.e., SST front). These SST fronts play an important role in the air-sea interaction in the mid-latitude regions. My study revealed that the SST front associated with the Kuroshio in the East China Sea enhance the Baiu rainband aloft in the mean state (Sasaki et al. 2012). In addition, Sasaki and Yamada (2018) showed that when the SST front is strong (weak), the precipitation anomaly is positive (negative) over the East China Sea and southern Japan (Fig. 4).
I also study the influence of oceanic variability on environmental change. One of the important issues of this topic is coastal sea level change, especially coastal sea level rise associated with the global warming. My studies revealed that the sea level rise along the southeastern coast of Japan is induced by the northward shift of the Kuroshio Extension (Fig. 5). In addition, I showed from a regional numerical simulation that the high sea level along the Japan coast around 1950 is caused by wind variability over the North Pacific (Sasaki et al. 2017). I also performed the simulation of the future sea level change in the western North Pacific (Liu et al. 2017).

Westward propagation of the jet-trapped Rossby wave
Sea surface temeprature trend in the western North Pacific
Propagation of salinity anomalies on subsurface layer
Precipitation changes associated with the sea surface temperature front variability of the Kuroshio
Coastal sea level change induced by Kuroshio Extension variability

Representative Achievements

Sasaki, Y. N., and Y. Yamada, 2018: Atmospheric response to interannual variability of sea surface temperature front in the East China Sea in early summer. Climate Dynamics, 51(7), 2509-2522.
Sasaki, Y. N., R. Washizu, T. Yasuda, and S. Minobe, 2017: Sea level variability around Japan during the 20th century simulated by a regional ocean model. Journal of Climate, 30, 5585-5595.
Sasaki, Y. N., S. Minobe and N. Schneider, 2013: Decadal response of the Kuroshio Extension jet to Rossby waves: Observation and thin-jet theory. Journal of Physical Oceanography, 43, 442-456.
Sasaki, Y. N., S. Minobe, T. Asai, and M. Inatsu, 2012: Influence of the Kuroshio in the East China Sea on the early summer (Baiu) rain. Journal of Climate, 25, 6627-6645.
Sasaki, Y. N., and N. Schneider, 2011: Decadal shifts of the Kuroshio Extension jet: Application of thin-jet theory. Journal of Physical Oceanography, 41, 979-993.
Academic degreePh. D. (Science)
Self Introduction

My research interests are dynamics of interannual to decadal oceanic fluctuations (e.g., jet) and air-sea interaction. I am also interested in the connection of these topics to climate and marine ecosystem.

Academic background2003: B. S.: Hokkaido University
2005: M. S.: Hokkaido University
2008: Ph. D.: Hokkaido University
2008-2010: Postdoctoral Fellow, International Pacific Research Center, University of Hawaii
2010-2011: Postdoctoral Fellow, Faculty of Science, Hokkaido University
2011-2013: Project Assistant Professor, Faculty of Science, Hokkaido University
2013-2018: Lecturer, Faculty of Science, Hokkaido University
2018-present: Associate Professor, Faculty of Science, Hokkaido University
Affiliated academic societyThe Oceanographic Society of Japan, The Meteorological Society of Japan, The American Geophysical Union
Room addressScience 8th building Room 8-3-20