Takuji Waseda

• Ph.D.
• Professor at The University of Tokyo

The Arctic Laptev and East Siberian seas (LESS) have high biogeochemical activity. Nutrient inputs associated with river runoff and shelf sediment–water exchange processes are vital for supporting primary production in the LESS. Relative to macronutrients, data on dissolved iron (dFe) and manganese (dMn), which are essential micronutrients for prim...

Sea ice is a key element of the global Earth system, with a major impact on global climate and regional weather. Unfortunately, accurate sea ice modeling is challenging due to the diversity and complexity of underlying physics happening there, and a relative lack of ground truth observations. This is especially true for the Marginal Ice Zone (MIZ),...

Sea ice is a key element of the global Earth system, with a major impact on global climate and regional weather. Unfortunately, accurate sea ice modeling is challenging due to the diversity and complexity of underlying physics happening there, and a relative lack of ground truth observations. This is especially true for the Marginal Ice Zone (MIZ),...

The statistics of the waves in the North Atlantic Ocean have been used as the basis of ship design for decades. Recently, there have been efforts to update the scatter diagram of wave height and period based on the numerical hindcast data combined with AIS data. However, the validation of the extreme wave distribution is problematic due to the lack...

The Arctic’s Laptev and East Siberian Seas (LESS) is a region with high biogeochemical activity. Nutrient inputs associated with river runoff and shelf sediment-water exchange processes are vital for supporting primary production in the LESS. However, the dynamics of trace metals such as iron (Fe) and manganese (Mn), which are essential micronutrie...

Waves critically modulate the air‐sea fluxes, and upper‐ocean thermodynamics in a Tropical Cyclone (TC) system. This study improves the modeling of TC intensification by incorporating non‐breaking wave‐induced turbulence and sea spray from breaking waves into an atmosphere‐ocean‐wave coupled model. Notably, wind forecast error decreased by around 1...

A drifting wave-ice buoy, which was configured by mounting the OpenMetBuoy on an ad hoc floating platform that we named Medusa, was deployed at the Lützow-Holm Bay (LHB) marginal ice zone in Antarctica on 4 Feb 2022 during the 63rd Japanese Antarctica research expedition. The wave-ice buoy, Medusa-766, survived the Antarctica winter as the measurem...

Progress in our understanding of wave–ice interactions is currently hindered by the lack of in situ observations and information of sea-ice properties, including the elastic modulus. Here, we estimate the effective elastic modulus of sea ice using observations of waves in ice through the deployment of three open-source geophone recorders on landfas...

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 an...

Science and Engineering of Freak Waves provides a holistic and interdisciplinary view of extreme ocean waves for both scientific and engineering applications. Readers will learn the fundamental theory of extreme waves and the implications they have on coastal structures and methods of prediction through chapters that review the definitions of extre...

The Marginal Ice Zone is a highly dynamic region where the atmosphere, ocean, waves and sea ice meet. Waves play a fundamental role in this coupled system, but progress in our understanding of wave-ice interactions is currently hindered by the lack of observations of sea ice properties in-situ. In this study we aim to estimate the ice thickness and...

Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. to this end, we have gathered a dataset of in-situ observations of...

Spume, large-radius seawater droplets that are ejected from the ocean into the atmosphere, can exchange moisture and heat fluxes with the surrounding air. Under severe weather conditions, spume can substantially mediate air-sea fluxes through thermal effects and thus needs to be physically parameterized. While the impact made by spume on air-sea in...

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 uncer...

Two drifting wave buoys were deployed in the central Arctic Ocean, north of the Laptev Sea, where there are historically no wave observations available. An experimental wave buoy was deployed alongside a commercial buoy. The inter-buoy comparison showed that the experimental buoy measured wave heights and periods accurately; so the buoy data were u...

In this study, we investigated the four-wave resonant and quasiresonant interactions in a special degenerated case, wherein bichromatic mother waves are generated to give birth to a daughter wave. One of the mother waves was counted twice to satisfy the four-wave resonant conditions. Particular attention is paid to the effect of finite water depth....

Ships avoid severe sea states for the safety of lives and property and to save energy. Therefore, the actual sea states encountered by ships differ from nature and are affected by human operational effects that we refer to as the “ship operational effect”. The evaluation of the ship operational effect is crucial for the rational design of structura...

Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. To this end, we have gathered a dataset of in-situ observations of...

Waves in the Marginal Ice Zone in the Okhotsk Sea are less studied compared to the Antarctic and Arctic. In February 2020, wave observations were conducted for the first time in the Okhotsk Sea, during the observational program by Patrol Vessel Soya. A wave buoy was deployed on the ice, and in situ wave observations were made by a ship-borne stereo...

The Akhmediev breather (AB) solution of the nonlinear Schrödinger equation (NLSE) shows that the maximum crest height of modulated wave trains reaches triple the initial amplitude as a consequence of nonlinear long-term evolution. Several fully nonlinear numerical studies have indicated that the amplification can exceed 3, but its physical mechanis...

The Akhmediev breather (AB) solution of the nonlinear Schr$\"{o}$dinger equation (NLSE) shows that the maximum crest height of modulated wave trains reaches triple the initial amplitude as a consequence of nonlinear long-term evolution. Several fully nonlinear numerical studies have indicated that the amplification can exceed 3, but its physical me...

Uncertainties of wave data and models got increasing attention in the last decades by the marine industry because of their importance for safety at sea. Improved knowledge about wave description and related uncertainties leads to a reduction of safety factors, and consequently building costs of marine structures. The ISSC (International Ship and Of...

Accurate ocean surface wave knowledge is crucial for ship design. With the significant advancements of model physics and numerical resources, the recent numerical wave hindcast data has a potential to provide environmental conditions for wave load estimation in the ship design process. This study aims to quantify model uncertainty in the state of a...

There is a wide consensus within the polar science, meteorology, and oceanography communities that more in situ observations of the ocean, atmosphere, and sea ice are required to further improve operational forecasting model skills. Traditionally, the volume of such measurements has been limited by the high cost of commercially available instrument...

JANUARY 10, 2022 There is a wide consensus within the polar science, meteorology, and oceanography communities 1 that more in-situ observations of the ocean, atmosphere, and sea ice, are required to further improve 2 operational forecasting model skills. Traditionally, the volume of such measurements has been limited 3 by the high cost of commercia...

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...

The ocean waves in the North Atlantic Ocean are internationally recognized to represent a wave climate suitable for the design of merchant ships. However, the accumulated knowledge from the past indicates that the encountered sea states are less severe than the Standard Wave Data recommended by the International Association of Classification Societ...

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...

The presence of coherent wave groups in the ocean has been so far postulated but still lacks evidence other than the indication from the radar images. Here, we attempt to reconstruct a wave field to monitor the evolution of a directional wave group based on a phase resolving two-dimensional non-linear wave model constrained by the stereo images of...

We experimentally investigated the influence of the geometries of a modulated wave train on the vertical-bending and torsional moments acting on a container ship in bow-quartering sea conditions. We conducted a towing experiment with a hydro-structural container ship model in the Actual Sea Model Basin (ASMB) (80 m deep, 40 m wide, and 4.5 m deep)...

Abstract We have explored tsunami current signals in maritime Automatic Identification System (AIS) data during the 2011 Tohoku, Japan, tsunami. The AIS data were investigated in detail taking into account ship motion and response to tsunami current. Ship velocity derived from AIS data was divided into two components in terms of the ship heading: h...

The sea ice coverage in the summer Arctic Ocean from the Beaufort to Laptev Seas continues to decrease, and the largest waves in the western Arctic open waters are increasing year by year. By looking into the historical wave events in the ERA-Interim reanalysis data, we discovered that more than half of the extreme events are caused by cyclones tha...

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 Oscil...

At reconnaissance to feasibility study stages of wave energy development, guidelines and standards recommend wave power assessments to be conducted for long periods of time, albeit at relatively coarse spatial resolutions. However, quite often developers need to make a preliminary site selection based on high-resolution information. Unfortunately,...

Soliton and breather solutions of the nonlinear Schrödinger equation (NLSE) are known to model localized structures in nonlinear dispersive media such as on the water surface. One of the conditions for an accurate propagation of such exact solutions is the proper generation of the exact initial phase-shift profile in the carrier wave, as defined by...

Emergence of pancake ice in the western Arctic Ocean is understood to be an effect of the increasing wave activity. During the 2018 R/V Mirai field campaign in the refreezing Chukchi Sea, we obtained observational evidence of sea ice formation that resembled the pancake cycle—frazil/pancake/consolidated pancake ice—first discovered and known to be...

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 c...

Extreme value analysis of significant wave height using data from a single location often incurs large uncertainty due to small sample size. Including wave data from nearby locations increases sample size at the risk of introducing dependency between extreme events and hence violating modelling assumptions. In this work, we consider extreme value a...

Surface ocean waves are one of the potential processes that influence on the Arctic sea-ice extent. A better understanding of the generation, propagation, and attenuation of ocean waves under the sea ice is necessary to discuss the future Arctic climate change. We deployed two drifting wave buoys in the marginal ice zone in the western Arctic. Sinc...

We examine and discuss the spatial evolution of the statistical properties of mechanically generated surface gravity wave fields, initialized with unidirectional spectral energy distributions, uniformly distributed phases, and Rayleigh distributed amplitudes. We demonstrate that nonlinear interactions produce an energy cascade towards high frequenc...

Soliton and breather solutions of the nonlinear Schr\"odinger equation (NLSE) are known to model localized structures in nonlinear dispersive media such as on the water surface. One of the conditions for an accurate propagation of such exact solutions is the proper generation of the exact initial phase-shift profile in the carrier wave, as defined...

Ocean surface waves are known to decay when they interact with sea ice. Wave–ice models implemented in a spectral wave model, e.g. WAVEWATCH III® (WW3), derive the attenuation coefficient based on several different model ice types, i.e. how the model treats sea ice. In the marginal ice zone (MIZ) with sea ice concentration (SIC) < 1, the wave atten...

The largest source of uncertainty in estimating annual energy production from a wave energy converter is natural variability. Standards recommend the collection of long-term on-site records, but with a concurrent requirement of dense data coverage, it becomes intractable to assess resources even at the feasibility development stage. Here, we provid...

The Korteweg–de Vries equation that describes surface gravity water wave dynamics in shallow water is well known to admit cnoidal wave solutions, i.e. periodic travelling waves with stationary wave shape. Such type of periodic wave patterns can be also found in the deep-water waves with the envelopes that follow the dynamics of the nonlinear Schröd...

We examine and discuss the spatial evolution of the statistical properties of mechanically generated wave fields, initialised with uniformly distributed phases and Rayleigh distributed amplitudes. We demonstrate that nonlinear interactions produce an energy cascade towards high frequency modes and triggers localised intermittent bursts. By analysin...

Sustaining an accurate, timely, and global tsunami forecast system remains a challenge for scientific communities. To this end, various viable geophysical monitoring devices have been deployed. However, it is difficult to implement new observation networks in other regions and maintaining the existing systems is costly. This study proposes a new an...

Accurate estimation of extreme wave condition is desired for the rational design of offshore structures, but the estimation results are known to have uncertainty from various sources. The quality and quantity of the available extreme wave data differ among ocean regions since the atmospheric cause of extreme waves are not identical. This paper prov...

Abstract. Satellite retrieved Sea Ice Concentration (SIC) uncertainty is studied with respect to its effect on spectral wave modelling of ice-covered water. Eight SIC products based on four algorithms applied to SSMIS and AMSR2 data were analysed. They were compared with sea-truth images captured from a 12 day fixed Marginal Ice Zone (MIZ) transect...

Inhomogeneous media can change the nonlinear properties of waves propagating on them. In the ocean, this phenomenon can be observed when waves travel on a surface current. In the case of negative horizontal velocity gradients (i.e. an accelerating opposing current or a decelerating following current), waves shorten and heighten, enhancing wave stee...

Freak/rogue waves are considered to be the causes of marine accidents and their generation mechanism is closely related to the formation of wave groups. However, observations that capture the spatiotemporal evolution of coherent wave groups in directional windsea are rather limited. The paper presents a new technique known as the surface wave recon...

Crowdsourcing using low-cost measurement sensors is becoming a possible option for environmental sciences. This study describes the development and demonstration experiment of a prototype of the low-cost observation system for wind over the ocean. A validation experiment of the low-cost anemometer showed calibration is necessary to use the sensor f...

This study proposes the detection of large offshore tsunamis by airborne radar. Altimeter measurements were carried out south of Japan by an observational aircraft along the Jason satellite tracks crossing over the Kuroshio Current. A nadir-pointing frequency-modulated continuous wave (FM-CW) radar and a global navigation satellite system (GNSS) ba...

The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps...

We seek to characterize the behavior of extreme waves in the Gulf of Mexico, using a 109 year-long wave hindcast (GOMOS). The largest waves in this region are driven by strong winds from hurricanes. Design of offshore production systems requires the estimation of extreme metocean conditions corresponding to return periods from 1 year to 10,000 year...

A stereo camera system was installed facing Southeast at the observational tower owned by the University of Tokyo in the Sagami Bay, Japan. The three-dimensional wave fields were reconstructed from the stereo images, which were successfully captured from April 2017 until now, by using an open source software WASS (Waves Acquisition Stereo System)....

Amplitude modulation of a propagating wave train has been observed in various media including hydrodynamics and optical fibers. The notable difference of the propagating wave trains in these media is the magnitude of the nonlinearity and the associated spectral bandwidth. The nonlinearity and dispersion parameters of optical fibers are two orders o...

Significance Understanding the fundamental dynamics of directional and localized waves is of significant importance for modeling ocean waves as well as predicting extreme events. We report a theoretical framework, based on the universal (2D + 1) nonlinear Schrödinger equation, that allows the construction of slanted solitons and breathers on the wa...

A towing experiment was conducted using a modulated wave train to investigate the vertical bending responses of a hydro-structural container ship model. In the experiment, a spatially periodic modulated wave train, as a model of a freak wave in successive high waves mimicking the so-called three sisters, was generated by the recently established hi...

Solitons and breathers are nonlinear modes that exist in a wide range of physical systems. They are fundamental solutions of a number of nonlinear wave evolution equations, including the uni-directional nonlinear Schr\"odinger equation (NLSE). We report the observation of slanted solitons and breathers propagating at an angle with respect to the di...

We investigated ship navigation records known as Automatic Identification System (AIS) data near the source region of the 2011 Tohoku, Japan, tsunami. The AIS data of 16 ships in the offshore navigation could be compiled by about 40 min after the tsunami generation. Most of the AIS data showed notable deviation of the ship heading from the course o...

We seek to improve estimation of extreme sea state severities offshore Japan. In this tropical cyclone-dominated region, magnitudes of large values of storm severity (significant wave height, HS) observed at a location of interest are highly dependent on the trajectories of tropical cyclones relative to the location. As a result, a naive estimate f...

Two freak waves were observed a day apart in October 2009 at a 5000-m deep moored station in the northwest Pacific Ocean. As the typhoon passed by, the wave system transitioned within a day from a narrow and unimodal spectrum to the broad and bi-modal spectrum. The occurrence probability of a freak wave is known to increase due to a modulational in...

A new wave generation method, called HOSM-WG, is presented in this paper. The method utilizes the precomputed spatially periodic wave field based on the higher-order spectral method (HOSM) simulation to calculate the wave-maker signals. The spatially periodic wave fields were reproduced in a rectangular basin with 382 wave makers on the peripheral....

The development of ocean waves under explosive cyclones (ECs) is investigated in the Northwestern Pacific Ocean using a hindcast wave simulation around Japan during the period 1994 through 2014. A composite analysis of the ocean wave fields under ECs is used to investigate how the spatial patterns of the spectral wave parameters develop over time....

A predictability study on wave forecast of the Arctic Ocean is necessary to help identify hazardous areas and ensure sustainable shipping along the trans-Arctic routes. To assist with validation of the Arctic Ocean wave model, two drifting wave buoys were deployed off Point Barrow, Alaska for two months in September 2016. Both buoys measured signif...

The long-term trends of the expected largest waves in the ice-free Arctic waters from Laptev to Beaufort Seas was studied analyzing the ERA-interim reanalysis from 1979 to 2016. The analysis showed that the positive trend is largest in October and increased almost 70 cm in 38 years. For ships navigating the Northern Ship Route, it is important to k...

This study proposes ideas to reproduce freak waves from observational data. The reproduced data will apply to investigations on freak wave impact to offshore structures. Four-dimensional variational method (4DVAR) was used for the freak wave reproduction. Under a dynamical constraint, 4DVAR minimizes the squared error between observation and model...

Modulation instability (MI) is one possible mechanism to explain the formation of extreme waves in uni-directional and narrow-banded seas. It can be triggered, when side-bands around the main frequency are excited and subsequently follow an exponential growth. In physical domain this dynamics translates to periodic pulsations of wave groups that ca...

This paper discusses the uncertainty in extreme wave analysis from different sources. Poor data quality and small sample size will lead to uncertainty in the extreme wave analysis. Extreme value estimation methods are developed based on various assumptions, and each would lead to unique estimation results. In addition, the cause of extreme waves va...

Izu island chain south of Tokyo, Japan has been considered as a prospective area for ocean renewable energy development because of relatively strong tidal currents, and the Kuroshio current. An Acoustic Doppler Current Profiler (ADCP) measurement near one of the islands, Kozu island, was conducted to know ocean current variability. The ADCP, Signat...

The long-term trend of extreme ocean waves in the emerging ice-free waters of the summer Arctic is studied using ERA-Interim wave reanalysis, with validation by two drifting wave buoys deployed in summer 2016. The 38-year-long reanalysis dataset reveals an increase in the expected largest significant wave height from 2.3 m to 3.1 m in the ice-free...

A number of studies on steep nonlinear waves were conducted experimentally with the temporally periodic and spatially evolving (TPSE) wave trains and numerically with the spatially periodic and temporally evolving (SPTE) ones. The present study revealed that, in the vicinity of their maximum crest height, the wave profiles of TPSE and SPTE modulate...

The transient response of a bay with a narrow mouth to incident tsunamis is interpreted as the convolution of the input signal with the impulse response obtained by an inverse Fourier transform of the response curve of the oscillatory system with one degree of freedom. The rate of radiation damping associated with energy escaping seaward through th...

A possible mechanism that is responsible for the occurrence of rogue waves in the ocean is the Benjamin–Feir instability or modulation instability. The deterministic framework that describes this latter instability of Stokes waves in deep water is provided by the family of Akhmediev breather (AB) solutions of the nonlinear Schrödinger equation (NLS...

This paper proposes a method to simultaneously measure wave profiles and particle velocity on a wave surface by stereo imaging. About 100 markers are used as floats in the measurement. The motion of the markers is tracked by stereo cameras. From the position of the markers, the wave profile and the particle velocity on the wave surface are estimate...

Tidal currents have two types of intrinsic long-term fluctuations. The one is single tidal constituent such as Ssa and the other one is interferences between tidal constituents. The effect of the long-term fluctuation of tides on the resource assessment for tidal current energy generation system near Japan has been described based on the prediction...

The future Nankai Trough tsunami is one of the imminent threats to the Japanese coastal communities that could potentially cause a catastrophic event. As a part of the countermeasure efforts for such an occurrence, this study analyzes the efficacy of combining tsunami data assimilation (DA) and waveform inversion (WI). The DA is used to continuousl...

There exists considerable disagreement among the observed values of the drag coefficient, CD. In order to develop a model of CD, the wind stress generally will be calculated from the eddy-correlation method. A buoy is suitable to measure the wind stress in many sea surface conditions. However, the motion correction is very difficult because the ane...

Ship height positioning by the Global Navigation Satellite System (GNSS) was investigated for measuring and forecasting great tsunamis. We first examined GNSS height-positioning data of a navigating vessel. If we use the kinematic precise point positioning (PPP) method, tsunamis greater than 10−1 m will be detected by ship height positioning. Based...

The applicability of hydrostatic approximation was studied by numerical simulations and theoretical speculations. By numerical simulations on tsunami propagation with soliton fission, it was found that the reproducibility of dispersive wave shape may be affected by horizontal grid size and non-hydrostatic pressure behind wave crest. Referring these...

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 mu...

Resource assessment is an essential step in the reconnaissance to feasibility study stages of marine renewable energy development. However, minimization of uncertainties associated with the estimation requires that data be provided at a sufficiently high resolution and duration long enough to include effects of climate variation. This paper describ...