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Wave streaming is a near-bottom mean current induced by the bottom drag on surface gravity waves. Wave variations include the variations in wave heights, periods, and directions. Here we use numerical simulations to study the effects of wave streaming and wave variations on the circulation that is driven by incident surface waves. Wave streaming induces an inner-shelf Lagrangian overturning circulation, which links the inner shelf with the surf zone. Wave variations cause alongshore-variable wave breaking that produces surf eddies; however, such eddies can be suppressed by wave streaming. Moreover, with passive tracers we show that wave streaming and wave variations together enhance the cross-shelf material transport.

The Kuroshio and tides significantly influence the oceanic environment off the Japanese mainland and promote mass/heat transport. However, the interaction between the Kuroshio and tides/internal waves has not been examined in previous works. To investigate this phenomenon, the two-dimensional high-resolution nonhydrostatic oceanic Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) model was employed. The results show that strong internal tides propagating upstream in the Kuroshio are generated at a near-critical internal Froude number (Fri = 0.91). The upstream internal wave energy flux reaches a magnitude of 12 kW m−1, which is approximately 3 times higher than that of internal waves without the Kuroshio. On the other hand, under supercritical conditions, the Kuroshio suppresses the internal wave energy flux. The interaction of internal tides and the Kuroshio also generates upstream propagating high-frequency internal waves and solitary wave packets. The high-frequency internal waves contribute to the increase in the total internal wave energy flux up to 40% at the near-critical Fri value. The results of this study suggest that the interaction of internal tides and the Kuroshio enhances the upstream propagating internal tides under the specified conditions (Fri ~ 1), which may lead to deep ocean mixing and transport at significant distances from the internal wave generation sites.

A numerical wave model is applied to study the wind‐generated wave in the Southern California Bight (SCB). Observational data available in this area are used to validate the numerical model results. The model is integrated for 10 years (2004–2013). The comparison of the model results with observations shows that the model well reproduces the wave variations in the SCB. The multiple‐scale variations in the wavefield are examined: interannual, seasonal, intraseasonal, and diurnal. The significant wave height and swell wave height distributions display distinct patterns during different seasons. On the interannual scale, the wave variation in the SCB is influenced by El Niño–Southern Oscillation activities. Intraseasonal scale events occur frequently. Land/sea breezes cause the diurnal variation. The effects of topography (especially islands) and currents on waves are analyzed. The islands in the SCB provide significant sheltering effects to the coast from deep‐ocean waves. The effect of background currents on waves is discussed.

Coastal fronts impact cross-shelf exchange of materials, such as plankton and nutrients, which are important to the ecosystems in continental shelves. Here using numerical simulation we demonstrate a nearshore front induced by wave streaming. Wave streaming is a bottom Eulerian current along the surface wave direction, and it is caused by the wave bottom dissipation. Wave streaming drives a Lagrangian overturning circulation in the inner shelf and pumps up deep and cold water into the overturning circulation. The water inside the overturning circulation is quickly mixed and cooled because of the wave streaming-enhanced viscosity. However, the offshore water outside the overturning circulation remains stratified and warmer. Hence, a front develops between the water inside and outside the overturning circulation. The front is unstable and generates submesoscale shelf eddies, which lead the offshore transport across the front. This study presents a new mechanism for coastal frontogenesis.

High-resolution downscaling ocean modeling was conducted to investigate the impacts of two super typhoons on the Kuroshio in the fall of 2014 off the Kyushu and Shikoku Islands, Japan. The model result was compared with field observations and satellite altimetry. The synoptic and mesoscale oceanic structures around the Kuroshio exhibit a good reproducibility. The typhoons generated near-inertial oscillations (NIOs) and near-inertial internal waves (NIIWs) around the Kuroshio path, particularly on the right side of the typhoon tracks. The NIOs developed in the mixed layer to alter the direction of the Kuroshio by ~30°. The associated velocity off the Shikoku and Kyushu Islands was significantly decelerated by ~0.2 ms −1 . The velocity almost vanished off Kyushu Island and thus induced an unstable fluctuating path shortly after both typhoons passed over that region. The NIIWs were also excited at the thermocline, resulting in the oscillation of the Kuroshio path occurred in the entire water column. In contrast, off Shikoku Island, the typhoons shifted the Kuroshio path northward to enhance the interactions with the topographies. This shift caused considerable eddy shedding from the capes that resulted in mesoscale counterclockwise circulations as cyclonic quasi-standing eddies with a shedding period of ~3 days in the north of the Kuroshio path. The magnitude, direction, and meridional location of the path of the Kuroshio prominently fluctuated with the propagation of these eddies, manifested off Shikoku Island. Furthermore, these eddies induced sporadic northward intrusions of the Kuroshio warm water through the Kii Channel into the Seto Inland Sea (SIS), where a weak but persisting southward outflow prevails under normal conditions. Therefore, the process could collectively be called the “typhoon-Kuroshio-eddy interaction”, which conceptually differs from the “typhoon-eddy-Kuroshio interaction” in the previous studies, where the Kuroshio was modulated by eddy collision. The wind stress curl and intrusions associated with the typhoons jointly provoked the inversion of the counterclockwise SIS residual circulation. The resultant spatially averaged volume flux was ~8 times as high as that under normal conditions.

Discovery and analysis of submesoscale variability O(0.3–30) km on the continental shelf is made possible by a high-resolution (Δx = 75 m) Regional Oceanic Modeling System (ROMS) simulation of the Southern California Bight (SCB). This variability is manifest in ubiquitous yet ephemeral coherent structures: fronts, filaments, and vortices. Similar to their open-ocean counterparts, fronts and filaments on the shelf are identified by their strong vertical velocity, surface convergence, cyclonic vorticity, and horizontal density gradient. Life cycles of these features typically last 3–5 days, with the formation dominated by a horizontal advective tendency that increases density and velocity gradients (i.e., frontogenesis). The shape of the coastline and depth of the water column both influence the abundance and spatial orientation of shallow-water fronts and filaments. Closer to shore, fronts and filaments often align themselves parallel to isobaths, and headlands often act as sites of intense vorticity generation through bottom stress. A quasi-steady, approximate momentum balance among rotation, pressure gradient, and vertical mixing—known as turbulent thermal wind (TTW)—often is valid in the strong secondary circulations local to fronts and filaments. However, front and filament circulations subject to strong diurnal variation in surface heating and vertical mixing are inconsistent with steady-state TTW balance. The secondary circulations can induce ephemeral material trapping and substantial vertical heat fluxes on the shelf.

A high-resolution, high-precision downscaling oceanic circulation model for the Southern China Sea (SCS) was developed based on the Regional Oceanic Modeling System (ROMS) at a lateral resolution of 5 km, initialized and forced by the HYbrid Coordinate Ocean Model (HYCOM) global reanalysis product. A multi-year reanalysis was conducted with the HYCOM-ROMS system that properly accounts for wind stress and heat budget at surface, freshwater influences from the atmosphere and major rivers, and tidal variability. Prospective applications of the system include assessments of oceanic dispersal of wastewater, quantification of marine ecosystem network, analyses of micro plastic transport and its coastal accumulation, etc. In prior to applied studies, we extensively investigated the validity and performance of the developed system. We found that it successfully reproduced primary dynamics of the SCS in many aspects such as the transient Kuroshio path in the south of Taiwan prominently affecting the circulation of the northern SCS through the Luzon Strait. The North Equatorial Current (NEC) drifting near Bismarck Archipelago, New Guinea, sporadically intrudes into the Indonesian water and adjacent seas to invoke bifurcating northward and westward currents. This intrusion promotes the northwestward mass transport into the Celebes Sea and further into the Sulu Sea, and then enters the SCS through the Palawan Strait.

In this study, an oceanic downscaling model in a double-nested configuration was used to investigate the role played by the Kuroshio warm current in preserving and maintaining biological diversity in the coral coasts around the Ryukyu Islands (Japan). A comparison of the modeled data demonstrated that the innermost submesoscale eddy-resolving model successfully reproduced the synoptic and mesoscale oceanic structures even without data assimilation. The Kuroshio flows on the shelf break of the East China Sea approximately 150–200 km from the islands; therefore, eddy-induced transient processes are essential to the lateral transport of material within the strip between the Kuroshio and the islands. The model indicated an evident predominance of submesoscale anticyclonic eddies over cyclonic eddies near the surface of this strip. An energy conversion analysis relevant to the eddy-generation mechanisms revealed that a combination of both the shear instability due to the Kuroshio and the topography and baroclinic instability around the Kuroshio front jointly provoke these near-surface anticyclonic eddies, as well as the subsurface cyclonic eddies that are shed around the shelf break. Both surface and subsurface eddies fit within the submesoscale, and they are energized more as the grid resolution of the model is increased. An eddy heat flux (EHF) analysis was performed with decomposition into the divergent (dEHF) and rotational (rEHF) components. The rEHF vectors appeared along the temperature variance contours by following the Kuroshio, whereas the dEHF properly measured the transverse transport normal to the Kuroshio's path. The diagnostic EHF analysis demonstrated that an asymmetric dEHF occurs within the surface mixed layer, which promotes eastward transport toward the islands. Conversely, below the mixed layer, a negative dEHF tongue is formed that promotes the subsurface westward warm water transport.

Characterizing the dispersion and dilution of storm water from small coastal creeks is important for understanding the importance of land-derived subsidies to nearby ecosystems and the management of anthropogenic pollutants. In Southern California, creek runoff is episodic, intense, and short-lived while the plumes are buoyant, all of which make the field sampling of freshwater plumes challenging. Numerical modeling offers a viable way to characterize these systems. The dilution and dispersion of freshwater from two creeks that discharge into the Santa Barbara Channel, California is investigated using Regional Ocean Modeling System (ROMS) simulations with a horizontal resolution of 100 m. Tight coupling is found among precipitation, hydrologic discharge, wind forcing, and submesoscale flow structures which all contribute to plume evolution. During flooding, plumes are narrow and attached to the coast, due to downwelling/onshore wind forcing and intense vorticity filaments lying parallel to the shelf. As the storm passes, the winds typically shift to offshore/upwelling favorable conditions and the plume is advected offshore which enhances its dilution. Plumes reach the bottom nearshore while they form thin layers a few meters thick offshore. Dilution field of passive tracers released with the runoff is strongly anisotropic with stronger cross-shelf gradients than along-shelf. Dispersion analysis of statistical moments of the passive tracer distribution results in scale-dependent diffusivities consistent with the particle-pair analysis of Romero et al. (2013). Model validation, the roles of submesoscale processes, and wind forcing on plume evolution and application to ecological issues and marine resource management are discussed.

Accurately representing diurnal and semidiurnal internal variability is necessary to investigate inner-shelf to midshelf exchange processes. Here, a coupled Regional Ocean Model System (ROMS)–Simulating Waves Nearshore (SWAN) model is compared to observed diurnal and semidiurnal internal tidal variability on the mid and inner shelf (26–8 m water depth) near San Pedro Bay, California. Modeled mean stratification is about one-half of that observed. Modeled and observed baroclinic velocity rotary spectra are similar in the diurnal and semidiurnal band. Modeled and observed temperature spectra have similar diurnal and semidiurnal band structure, although the modeled is weaker. The observed and modeled diurnal and semidiurnal baroclinic velocity- and temperature-dominant vertical structures are similar and consistent with mode-one internal motions. Both observed and modeled diurnal baroclinic kinetic energy are strongly correlated to diurnal wind forcing and enhanced by subtidal vorticity-induced reduction in the inertial frequency. The mid- and inner-shelf modeled diurnal depth-integrated heat budget is a balance between advective heat flux divergence and temperature time derivative. Temperature–velocity phase indicates progressive semidiurnal internal tide on the midshelf and largely standing internal tide on the inner shelf in both observed and modeled. The ratio of observed to modeled inferred phase speed is consistent with the observed to modeled stratification. The San Pedro Bay modeled semidiurnal internal tide has significant spatial variability, variable incident wave angles, and multiple local generation sites. Overall, the coupled ROMS–SWAN model represents well the complex diurnal and semidiurnal internal variability from the mid to the inner shelf.

Rip currents arise from the momentum flux associated with depth-induced breaking of incident surface gravity waves on beaches with irregular bottom topography. In 3D simulations with an idealized topographic configuration, uniform density, and a steady incident wave field, a striking enhancement of transient surf eddy variability occurs over irregular topography compared to smooth topography, especially at nearly normal incident wave angles. Alternatively, with highly oblique incident waves, transient shear instability is observed over smooth topography whereas for irregular topography, standing rip eddies are generated. In the presence of larger-scale coastline variations, mega-rip circulations emerge, and they are especially strong for embayments. In all cases with significant transient surf-eddy activity, the eddy-induced mean horizontal transport is a non-trivial component of the total mean transport, and sometimes it is much larger than the gravity-wave Stokes drift. Typically the transport by the eddy-induced flow partially cancels the Eulerian transport by the time- and/or alongshore-averaged currents, but not by enough to reverse the “residual” pattern of total transport.

The dispersal and dilution of urban wastewater effluents from offshore, subsurface outfalls is simulated with a comprehensive circulation model with downscaling in nested grid configurations for San Pedro and Santa Monica Bays in Southern California during Fall of 2006. The circulation is comprised of mean persistent currents, mesoscale and submesoscale eddies, and tides. Effluent volume inflow rates at Huntington Beach and Hyperion are specified, and both their present outfall locations and alternative nearshore diversion sites are assessed. The effluent tracer concentration fields are highly intermittent mainly due to eddy currents, and their probability distribution functions have long tails of high concentration. The dilution rate is controlled by submesoscale stirring and straining in tracer filaments. The dominant dispersal pattern is alongshore in both directions, approximately along isobaths, over distances of more than 10 km before dilution takes over. The current outfall locations mostly keep the effluent below the surface and away from the shore, as intended, but the nearshore diversions do not.

Knowledge of horizontal relative dispersion in nearshore oceans is important for many applications including the transport and fate of pollutants and the dynamics of nearshore ecosystems. Two-particle dispersion statistics are calculated from millions of synthetic particle trajectories from high-resolution numerical simulations of the Southern California Bight. The model horizontal resolution of 250 m allows the investigation of the two-particle dispersion, with an initial pair separation of 500 m. The relative dispersion is characterized with respect to the coastal geometry, bathymetry, eddy kinetic energy, and the relative magnitudes of strain and vorticity. Dispersion is dominated by the submesoscale, not by tides. In general, headlands are more energetic and dispersive than bays. Relative diffusivity estimates are smaller and more anisotropic close to shore. Farther from shore, the relative diffusivity increases and becomes less anisotropic, approaching isotropy ~10 km from the coast. The degree of anisotropy of the relative diffusivity is qualitatively consistent with that for eddy kinetic energy. The total relative diffusivity as a function of pair separation distance R is on average proportional to R5/4. Additional Lagrangian experiments at higher horizontal numerical resolution confirmed the robustness of these results. Structures of large vorticity are preferably elongated and aligned with the coastline nearshore, which may limit cross-shelf dispersion. The results provide useful information for the design of subgrid-scale mixing parameterizations as well as quantifying the transport and dispersal of dissolved pollutants and biological propagules.

A vortex-force formalism for the interaction of surface gravity waves and currents is implemented in a three-dimensional (3D), terrain-following, hydrostatic, oceanic circulation model (Regional Oceanic Modeling System: ROMS; Shchepetkin and McWilliams, 2005 ). Eulerian wave-averaged current equations for mass, momentum, and tracers are included in ROMS based on an asymptotic theory by McWilliams et al. (2004) plus non-conservative wave effects due to wave breaking, associated surface roller waves, bottom streaming, and wave-enhanced vertical mixing and bottom drag especially for coastal and nearshore applications. The currents are coupled with a spectrum-peak WKB wave-refraction model that includes the effect of currents on waves, or, alternatively, a spectrum-resolving wave model (e.g., SWAN) is used. The coupled system is applied to the nearshore surf zone during the DUCK94 field measurement campaign. Model results are compared to the observations and effects of parameter choices are investigated with emphasis on simulating and interpreting the vertical profiles for alongshore and cross-shore currents. The model is further compared to another ROMS-based 3D coupled model by Warner et al. (2008) with depth-dependent radiation stresses on a plane beach. In both tests the present model manifests an onshore surface flow and compensating offshore near-bed undertow near the shoreline and around the breaking point. In contrast, the radiation-stress prescription yields significantly weaker vertical shear. The currents’ cross-shore and vertical structure is significantly shaped by the wave effects of near-surface breaker acceleration, vertical component of vortex force, and wave-enhanced pressure force and bottom drag.

Hydrodynamics, sediment suspension, and morphological response on an estuarine intertidal sand flat in Tokyo Bay, Japan, are examined through a field experiment performed for 16 days in winter 2000 and using a bathymetry data set based on a 6-year series of surveys. Topography of the sandy flat was found to fluctuate by approximately 8 cm during the deployment, while the long-term accumulation rate is estimated with the surveyed bathymetries to be only 3.8 cm/y. Cross-spectral analysis of the measured data indicates that on the sandy tidal flat, semidiurnal or shorter-period fluctuations in current velocity are mostly attributed to semidiurnal tides and waves, whereas wind above the sea generally drives diurnal or longer-period fluctuations. The field data also confirm that suspended sediment concentrations were highly correlated with bed shear stress, which is generated by combination of tidal current, wind-induced current, and wind waves. Episodic erosion is observed on the sandy flat with high...

A coupled wave and circulation model that includes tide, wind, buoyancy, and wave processes is necessary to investigate tracer exchange in the shelf region. Here, a coupled Regional Ocean Model System (ROMS)–Simulating Waves Nearshore (SWAN) model, resolving midshelf to the surfzone region of the San Pedro Bay, California, is compared to observations from the 2006 Huntington Beach experiment. Waves are well modeled, and surfzone cross- and alongshore velocities are reasonably well modeled. Modeled and observed rotary velocity spectra compare well in subtidal and tidal bands, and temperature spectra compare well in the subtidal band. Observed and modeled mid- and inner-shelf subtidal velocity ellipses and temperature variability determined from the first vertical complex EOF (cEOF) mode have similar vertical structure. Although the modeled subtidal velocity vertical shear and stratification are weaker than observed, the ratio of stratification to shear is similar, suggesting model vertical mixing is consistent with observations. On fortnightly and longer time scales, the surface heat flux and advective heat flux divergence largely balance on the inner shelf and surfzone. The surfzone and inner-shelf alongshore currents separated by 220 m are unrelated. Both modeled and observed subtidal alongshelf current and temperature are cross-shelf coherent seaward of the surfzone. Wind forcing explains 50% of the observed and modeled inner-shelf alongshore current variability. The observed and modeled inner-shelf alongshelf nonuniformities in depth-averaged alongshore velocities are similar. Inferred, inner-shelf, wave-induced, cross-shore exchange is more important than on the U.S. East Coast. Overall, the coupled ROMS–SWAN model represents well the waves and subtidal circulation dynamics from the midshelf to the surfzone.

導流堤を有する感潮湖湖口周辺海岸の地形変化を検討するために, 静岡県浜名湖今切口において導流堤の建設中および建設後の30年間に取得された25枚の深浅データを経験的複素固有関数法などによって解析した. その結果, 引き潮によって生じた深みが解析期間中深くなっていること, 解析期間前半では湖口両側に形成された浅瀬は岸向きに移動していたけれども解析期間後半には漂砂上手側の浅瀬の移動方向が沖向きに変化したことを明らかにした. さらに, 湖口の漂砂上手側における堆積量は時間とともに減少するにもかかわらず下手の海岸に供給される土砂量は増加していないこと, これは導流堤を通過した土砂が引き潮デルタに捕捉されたためであること, デルタに捕捉された土砂の量は1992年にほぼ平衡状態に達していたことなどを示した.

自然干潟における浮遊砂の生成, 砂面変動等に代表される漂砂の基本特性を把握することを目的として, 冬期の東京湾盤洲干潟において, 波, 流れ, 浮遊砂, 地形に関する短期の現地観測を行った. その結果, 下げ潮時に大きな波浪が来襲し, かつ風の吹送方向と潮汐流の方向が一致したときに大量の浮遊砂が生成されて侵食が進行するという, 有意な地形変化を捉えることに成功した. 盤洲干潟は長期的には3.8cm/yの速度で徐々に堆積しているものの, 本観測では, 高濃度の浮遊砂が断続的に発生するイベントによって, 16日間の観測期間中に最大8cm程度の侵食が生じていた. また, シールズ数を用いた検討の結果, 盤洲干潟の底質移動には浮遊砂が大きく寄与していること, 潮汐による水深変化に追従して変動する波浪が高濃度の浮遊砂の発生に対して重要な役割を果たしていることなどを明らかにした.

海岸帯水層中の地下水の挙動を数値モデルによって調べた. まず, 飽和-不飽和浸透流式と塩分の移流分散方程式を連立させ, 海面の時間変動を境界条件として取り込むことにより, 海岸帯水層特有の地下密度流場を解き, かつ帯水層中に形成される塩水楔の非定常過程を解析し得る数値モデルを示した. この数値モデルを用いて, 砂浜海岸における帯水層中の浸透流場を解析した結果, 前浜表層においてH. W. L. の汀線付近で下向き, L. W. L. の汀線付近で上向きの, 局所的な循環流が形成され, 海水が滞留する領域が出現することを明らかにした. さらに, その形成メカニズムに関する考察を行い, 循環流が潮汐の作用によって形成されたものであること, 帯水層中の密度構造と密接に関連していること, 陸域からの淡水フラックスの大小, 潮位振幅, 海浜勾配等によってもその形態が大きく変化することを見出した.

Submarine groundwater discharge (SGWD) and associated nutrient fluxes at Hasaki Beach along the Kashima coast in Japan were investigated through field measurements and numerical simulations. The field data indicate that (1) groundwater has higher concentrations of land-derived nutrients than seawater and river water; (2) microbial activity near the shoreline is likely to induce mineralization, reduction, and oxidation of nitrogen and phosphorus; and (3) in the portion of the aquifer underlying coastal forest, nitrate is appreciably reduced. A numerical model incorporating effects of water table and tidal fluctuations was developed to evaluate SGWD. Assuming that the aquifer consists of homogeneous sandy soil, the simulation results show that the nutrient flux due to SGWD is less than that of Tone River discharge. The nutrient flux via groundwater seepage is considered to be a minor component of primary productivity in the surf zone.

成層期における海-陸境界部としての極浅海域特有の水環境特性を, 東京湾奥部人工海浜海域を対象とした現地観測と, 数値計算により検討した. 現場海域の水温構造は風速と日射量の変動特性にかなり依存しており, 微風時には潮位変動に伴う沖側底層水塊の貫入が発生し, 強い沖出し風が連吹すると沿岸湧昇により沖側底層水塊の湧昇が起こる. 境界部である海岸域では貧酸素水の湧昇の影響により強い青潮が生じるとともに, 青潮後のブルーミングにより赤潮状態へと移行する. また, 水深が浅いほど日射の影響を強く受け, その結果, 水温成層構造に明確な岸沖分布が形成されるとともに, 水温・溶存酸素量・植物プランクトン量等の日周変動レベルが極めて大きくなる. さらに, 極浅海域では沖側と比較して, 風によって引き起こされる湧昇や吹き寄せなどに伴う水平移流による熱フラックスが, 日周期および長周期の水温変動特性に大きく寄与していることなどを明らかにした.

[1] The generation mechanisms and properties of the mesoscale eddies in the northeastern tropical Pacific (NETP) are studied using a series of numerical solutions and satellite observations. The spatial and temporal resolution of mountain wind jets over the Gulfs of Tehuantepec and Papagayo are essential for an accurate modeling of the regional mesoscale variability. Three previously proposed eddy generation mechanisms are the local transient wind forcing, the combined low-frequency wind and boundary forcing, and the remote equatorial Kelvin wave forcing. In our model, the transient wind-forcing was represented by wind fields with synoptic variability, and the remote equatorial Kelvin wave forcing by 5-day open boundary conditions with interannual variability. Solutions with and without high-frequency forcings are contrasted to evaluate the contributions of the three mechanisms. The combined low-frequency wind and boundary forcing is the primary eddy forcing mechanism in the NETP. In the Tehuantepec region, the high-frequency wind-forcing contributes more to the mesoscale variability than the remote equatorial Kelvin wave forcing, while in the Papagayo region, their contributions are comparable. Eddies in the Tehuantepec and Papagayo regions are larger in both amplitude and size, and are more likely to deflect equatorward than eddies in the rest of the NETP. The maximum temperature anomaly of eddies is at around 50 m depth. Eddies with lifetimes >6 weeks are more likely anticyclonic, while eddies with lifetimes

The Regional Oceanic Modeling System (ROMS) is applied in a nested configuration with realistic forcing to the Southern California Bight (SCB) to analyze the variability in semidiurnal internal wave generation and propagation. The SCB has a complex topography with supercritical slopes that generate linear internal waves at the forcing frequency. The model predicts the observed barotropic and baroclinic tides reasonably well, although the observed baroclinic tides feature slightly larger amplitudes. The strongest semidiurnal barotropic to baroclinic energy conversion occurs on a steep sill slope of the 1900-m-deep Santa Cruz Basin. This causes a forced, near-resonant, semidiurnal Poincaré wave that rotates clockwise in the basin and is of the first mode along the radial, azimuthal, and vertical directions. The associated tidal-mean, depth-integrated energy fluxes and isotherm oscillation amplitudes in the basin reach maximum values of about 5 kW m−1 and 100 m and are strongly modulated by the spring–neap cycle. Most energy is locally dissipated, and only 10% escapes the basin. The baroclinic energy in the remaining basins is orders of magnitudes smaller. High-resolution coastal models are important in locating overlooked mixing hotspots such as the Santa Cruz Basin. These mixing hotspots may be important for ocean mixing and the overturning circulation.

[1] A young cold core cyclonic eddy displaying a significant increase in surface chlorophyll was observed offshore Lanai Island, Hawai'i, where the Marine Optical Buoy (MOBY) is located. During one of its deployments, MOBY broke free from its mooring. In the course of its 3-day free drifting period, MOBY followed a cyclonic eddy, which is manifested by satellite remote sensing data, chlorophyll data from Moderate Resolution Imaging Spectroradiometer, and sea surface temperature (SST) from a Geostationary Operational Environmental Satellite. The time series of the SST show that the cold core eddy was in a formative stage. It existed as a stand-alone eddy for about 9 days before it merged with cold water south of Oahu Island. A high-resolution numerical model simulation reproduces similar eddies in terms of location, size, and intensity. An eddy detection algorithm is described and applied to locate and track the modeled eddies. The results demonstrate that mesoscale and submesoscale eddies are frequently generated on and pass through the lee side of Lanai Island and the statistical analysis quantifies the general features of eddies in the area.

[1] Oceanic infragravity waves are investigated as a possible source of seismic free oscillations, often referred to as the “hum” of the Earth, using a numerical model of depth-independent, nondispersive, long-wave dynamics with a forcing from nonlinear interactions among the primary wind waves (including swell). Because of near-resonant amplification, the structure of the primary-wave forcing field in shallow water, and an edge-trapping mechanism, infragravity waves are excited very effectively near the coasts. Deep-water infragravity waves are significantly influenced both by offshore leakage and propagation of the coastally generated free waves and by deep-water primary-wave forcing. With the inclusion of “mesoscale” variability on top of the more slowly varying primary waves generated in synoptic storms, the deep-water infragravity waves are found to have an amplitude on the order of a millimeter in height, which is consistent with field observations and considered to be sufficient to account for local hum excitation in the middle of the basin.

Wave-current interaction is incorporated into the Regional Ocean Modeling System (ROMS) on the basis of the multi-scale asymptotic theory derived by McWilliams et al. (2004) using a vortex force formalism to investigate its importance in a wide range of coastal oceanic phenomena. The relationship between different wave-averaged current theories, in particular with a widely-used radiation stress formalism, is explored (Lane et al., 2007). A forced dissipative long-wave model is developed for generation and propagation of deep-ocean infragravity waves in conjunction with the excitation mechanism of Earth's seismic free oscillation on the ocean floor (Uchiyama and McWilliams, 2008). An investigation of shear instability due to breaking-wave-driven barotropic littoral currents on a barred beach is being carried out by extending the asymptotic theory appropriate for a strong current regime near surf zones with a parameterized, non-conservative wave breaking (Uchiyama et al., 2008).

Complex principal component analysis (CPCA) is applied to examine medium-term geomorphological behavior of an exposed sandy beach adjacent to a gigantic breakwater of the Port of Sendai located near a river mouth in the Sendai Coast, Japan, using a 12-year series of bathymetry survey data. The results of CPCA and conventional real-PCA demonstrate that erosion and subsequent accretion of the submerged terrace formed in front of the river mouth appear in the first mode of CPCA and have the most significant influence on the medium-term geomorphology of the study area. The first mode is mostly caused by northward alongshore sediment transport driven by wave energy flux, explained from the observed wave data. The second mode of CPCA demonstrates that the sediments previously discharged from the river return again into the nearshore region, and furthermore, the topography changes due to cross-shore sediment transport emerge in the third mode of CPCA.