Tsubasa Kodaira 교수

Internal solitary waves in a system of two fluids, silicone oil and water, bounded above by a free surface are studied both experimentally and theoretically. By adjusting an extra volume of silicone oil released from a reservoir, a wide range of amplitude waves are generated in a wave tank. Wave profiles as well as wave speeds are measured using multiple wave probes and are then compared with both the weakly nonlinear Korteweg–de Vries (KdV) models and the strongly nonlinear Miyata–Choi–Camassa

Arctic sea ice is rapidly decreasing during the recent period of global warming. One of the significant factors of the Arctic sea ice loss is oceanic heat transport from lower latitudes. For months of sea ice formation, the variations in the sea surface temperature over the Pacific Arctic region were highly correlated with the Pacific Decadal Oscillation (PDO). However, the seasonal sea surface temperatures recorded their highest values in autumn 2018 when the PDO index was neutral. It is shown

Abstract. Observations of wave dissipation and dispersion in sea ice are a necessity for the development and validation of wave–ice interaction models. As the composition of the ice layer can be extremely complex, most models treat the ice layer as a continuum with effective, rather than independently measurable, properties. While this provides opportunities to fit the model to observations, it also obscures our understanding of the wave–ice interactive processes; in particular, it hinders our a

The significant reduction of the sea ice extent in the western Arctic has been observed by the sustained satellite observations since 1979. The opening ocean is now allowing waves to evolve and propagate under the presence of the Arctic sea ice. A better understanding of the wave-ice interaction is necessary for the safe shipping over the sea ice covered Arctic Ocean and to improve the Arctic climate projection. During R/V Mirai Arctic Expedition in October 2019, two drifting wave-buoys were con

With the long-term goal of developing an operational forecast system for total water level, we conduct a hindcast study of global storm surges for Fall 2014 using a baroclinic ocean model based on the NEMO framework. The model has 19 vertical levels, a horizontal resolution of 1/12°, and is forced by hourly forecasts of atmospheric wind and air pressure. Our first objective is to evaluate the model’s ability to predict hourly sea levels recorded by a global array of 257 tide gauges. It is shown

Abstract Global M 2 tidal surface currents are predicted using a global baroclinic ocean model with horizontal grid spacing of 1/12° and 19 z‐levels in the vertical. After first showing the predicted tidal elevations are in reasonable agreement with observations made by bottom pressure recorders and altimeters, the predicted tidal surface currents are evaluated by comparing them with independent estimates based on observed drifter trajectories. Both predicted and observed tidal surface currents

Accurate knowledge of ocean surface waves is crucial for ship design. With the significant advancements in model physics and numerical resources, recent numerical wave hindcast data has the potential to provide environmental conditions for estimating the wave load in the ship design process. To help estimate extreme wave loads with quantified uncertainty for strength assessments of ship structures, this study aims to quantify model uncertainty in the state-of-the-art numerical wave hindcast prod

The interaction between waves and ice has a crucial impact on the seasonal change in the sea ice extent. However, our comprehension of this phenomenon is restricted by a lack of observations. In recent years, availability of the low-cost and accurate Inertial Motion Units has enabled the development of affordable wave research devices. Despite advancements in designing innovative open-source instruments optimized for deployment on ice floes, their customizability and survivability remain limited

Driven by technical advances in low-cost electronics, massive deployment of ocean sensing devices has become increasingly feasible. We have developed an inexpensive MEMS IMU based and solar-powered small wave buoy FZ that makes the intensive deployments possible. After the hardware and software of the developed wave buoy is described, the results of the test deployments of the four FZ wave buoys to the Okhotsk Sea with the seasonal sea ice coverage in February 2022. For reference, the commercial

Abstract Nonlinear internal waves (NIWs) induce strong surface currents which are observable in synthetic aperture radar (SAR) images. SAR images of the Kuroshio show parabolic features around Japan's Izu Islands implying possible NIWs. Most images were taken during the summer when the Kuroshio approached the islands, and the winds were relatively weak. Nonhydrostatic numerical simulations revealed that around the islands, mode 1 internal waves are not trapped but higher modes, with lower propag

Abstract. Observations of wave dissipation and dispersion in sea ice are a necessity for the development and validation of wave-ice interaction models. As the composition of the ice layer can be extremely complex, most models treat the ice layer as a continuum with effective, rather than independently measurable, properties. While this provides opportunities to fit the model to observations, it also obscures our understanding of the wave-ice interactive processes, particularly, it hinders our ab

Abstract With the long-term goal of developing an ensemble forecast system for coastal flooding, we are developing a dynamically-based, numerical model of the global ocean. The model is based on the NEMO framework and has been used to predict global tides and surges in previous studies. This study focuses on the optimization of the joint prediction of both tides and surges, the two main components of total water level that cause coastal flooding. To improve the predictions of the tide we use a m

In the polar regions, the interaction between waves and ice has a crucial impact on the seasonal change in the sea ice extent. However, our comprehension of this phenomenon is restricted by a lack of observations, which, in turn, results in the exclusion of associated processes from numerical models. In recent years, availability of the low-cost and accurate Inertial Motion Units has enabled the development of affordable wave research devices. Despite advancements in designing innovative open-so