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We performed oceanic and atmospheric observations in the region off the Sanriku coast, Japan, from May 11 to 5 July 2022, using a wave-propelled unmanned surface vehicle, a Wave Glider (WG). Despite the severe weather conditions of atmospheric low-pressure system crossings, we successfully measured wind, air temperature, humidity, and sea surface temperature over the course of 55 days to calculate the turbulent heat flux. The WG observed that the atmosphere became more humid due to the southerly wind along the northwestern rim of the North Pacific subtropical high. The warm Kuroshio water expanded to the southeast of Hokkaido as a result of the northward shedding of an anticyclonic mesoscale (~100 km) eddy, called a warm-core ring, from the Kuroshio Extension. The WG traversed smaller (sub-mesoscale) water regions that were warmer and saltier than the surrounding Kuroshio water. The observations indicate that cold, dry air masses advected by northerly winds following the passage of atmospheric low-pressure systems generate a substantial upward turbulent heat flux over sub-mesoscale warm water regions, contrasting to no heat flux in the surrounding Kuroshio water region.

Kim, T. and Lee, J., 2024. Comparative analysis of wave data observed from the wave glider system and satellites. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 553-557. Charlotte (North Carolina), ISSN 0749-0208 Offshore wave data are crucial for model verification and as boundary conditions for coastal wave models. However, obtaining these measurements using buoy systems or ocean tower stations is complex. Notably, the offshore of the East Sea lacks in-situ observational data to use as model boundary conditions or to validate satellite observations, which motivated the deployment of a wave glider system. This system was operated from October 16, 2015, to October 21, 2016, and from January 2, 2017, to March 31, 2017, in the East Sea (130.9°E and 36.48°N). The wave glider measured wave heights, periods, and directions at 30-minute intervals. This study evaluates the quality of the wave data collected by the wave glider and assesses its feasibility for use in the East Sea. Significant wave heights from available satellite data were compared with those from the wave glider, and the wave directional spectrum was analyzed during high wave conditions. Accurate offshore wave observations enable more precise estimation of external forces impacting the coast.

The sub‐seasonal CO2 flux (FCO2) variability across the Southern Ocean is poorly understood due to sparse observations at the required temporal and spatial scales. Twinned surface and profiling gliders experiments were used to investigate how storms influence FCO2 through the air‐sea gradient in partial pressure of CO2 (ΔpCO2) in the sub‐Antarctic zone. Winter‐spring storms caused ΔpCO2 to weaken (by 22–37 μatm) due to mixing/entrainment and weaker stratification. This weakening in ΔpCO2 was in phase with the increase in wind stress resulting in a reduction of the storm‐driven CO2 uptake by 6%–27%. During summer, stronger stratification explained the weaker sensitivity of ΔpCO2 to storms, instead temperature changes dominated the ΔpCO2 variability. These results highlight the importance of observing synoptic‐scale variability in ΔpCO2, the absence of which may propagate significant biases to the mean annual FCO2 estimates from large‐scale observing programmes and reconstructions. Plain Language Summary The sub‐Antarctic zone of the Southern Ocean is a region that mostly experiences carbon dioxide (CO2) uptake because of its low temperature, strong winds and lower CO2 content. The wind can influence the CO2 uptake through two pathways: the speed of CO2 transfer between the air‐sea interface (kw) and the difference in CO2 concentration in the surface ocean and overlying atmosphere (ΔpCO2). Using autonomous robots that can measure hourly air and water conditions simultaneously, we show that not resolving ΔpCO2 during a storm event can lead to overestimating the CO2 uptake. This is particularly important during winter and spring when the ocean's surface layers are less stratified. The warmer temperatures during summer meant a more stratified surface layer resulting in a weaker and delayed impact of storms on the ΔpCO2. This study shows that the various annual CO2 uptake estimation methods used by the research community should not neglect ΔpCO2 responses during storms. Key Points Hourly glider observations show that the impact of storms on both kw and ΔpCO2 simultaneously modulates the ocean CO2 uptake variability Winter‐spring storms weaken ΔpCO2 through enhanced entrainment and mixing, partially counteracting the increase in CO2 uptake due to kw alone By not accounting for the storm‐linked positive feedback in ΔpCO2, the cumulative seasonal CO2 uptake was found to be overestimated by ∼6%

With the increasing use of autonomous surface vehicles (ASVs) to characterize the marine atmospheric boundary layer, better understanding and evaluation of the observations collected from these platforms is needed. We present here unique comparisons of measurements of bulk properties and air‐sea fluxes collected from ASVs right above the sea surface to state‐of‐the‐art observations from R/P FLIP over a broad range of environmental conditions. We find good agreement between the two platforms, suggesting that near surface observations from such wave following vehicles are suitable to estimate air‐sea fluxes using bulk formulas. This result is somewhat surprising, because the relatively low measurement height (1 m) is often below the wave crests. Possible interpretations are that the presence of waves does not violate the assumptions of the Monin‐Obukhov theory inherent in the TOGA COARE bulk flux formulas, or that the empirical fit of the Monin‐Obukhov stability functions somehow accounts for the wave effects.

Wave glider is an unmanned surface vehicle that can directly convert wave energy into forward propulsion and fulfill long-term marine monitoring. A previous study suggested that the wave motion and stiffness of restoring springs mounted on the hydrofoil are the main factors affecting the propulsion performance of the wave glider. In this paper, the dynamic responses and nonlinear characteristics of the underwater propulsion mechanism considering the nonlinear stiffness of restoring springs are investigated based on a fluid–rigid body coupled model. Firstly, models of propulsion mechanism with different kinds of restoring springs are proposed, and the linear and nonlinear characteristics of the restoring spring are considered. Then, a fluid–rigid body coupled model of a wave glider is developed by coupling the rigid body dynamics model and hydrodynamic model. Dynamic responses are simulated by the numerical analysis method, and the nonlinear characteristics with different restoring springs are illustrated by the time/frequency domain motion response and phase diagram analysis. The effects of the wave excitation frequency, wave heights and the location of the connection point of springs on the propulsion performance of the wave glider are analyzed. The results show that multi-frequency responses occurred in the propulsion system, and the nonlinear restoring spring on the hydrofoil can provide a larger restoring moment to avoid excessive pitch angle and is more suitable for different sea conditions, which provides a reference for developing propulsion mechanisms with high performance in complex marine environments.

Possessing the world's largest Exclusive Economic Zone (EEZ), the United States enjoys the benefits of a multi-billion dollar commercial fishing industry. Along with these benefits comes the enormous task of assessing the status of the nation's commercial fish stocks. At present, many of the most valuable commercial fish stocks are assessed using acoustic surveys conducted from manned survey vessels. The expense and limited availability of ship time often compromise the quantity and quality of the acoustic stock assessment data being collected. Here, we describe our vision for how an unmanned mobile platform, the Liquid Robotics Wave Glider, can be used in large numbers to supplement manned survey vessels and transform fisheries acoustics into a science more consistent with the new ocean-observing paradigm. Wave Gliders harness wave energy for propulsion and solar energy to power their communications, control, navigation, and environmental-​sensing systems. This unique utilization of wave and solar energy allows Wave Gliders to collect ocean environmental data sets for extended periods of time. Recently, we developed new technology for Wave Gliders that enable them to collect multifrequency, split-beam acoustic data sets comparable to those collected with manned survey vessels. A fleet of Wave Gliders collecting such data would dramatically improve the synoptic nature as well as the spatial and temporal coverage of acoustic stock assessment surveys. With improved stock assessments, fisheries managers would have better information to set quotas that maximize yields to fishermen and reduce the likelihood of overfishing. Improved observational capabilities also would enable fisheries scientists and oceanographers to more closely monitor the responses of different fish stocks to climate variability and change as well as ocean acidification.

The occurrence of humpback whales ( Megaptera novaeangliae) across the 2600 km of Hawaiian archipelago, which include the remote atolls, banks, and seamounts of Papahānaumokuākea Marine National Monument (PMNM), remains poorly understood. Previous surveys for humpback whales beyond the main Hawaiian Islands have been scarce due to limited access and the challenging winter conditions typically found in PMNM when whales are present. To overcome these limitations, a combination of moored acoustic recorders and a Wave Glider autonomous surface vehicle were used to acoustically monitor eight locations and survey approximately 1500 km of the Hawaiian archipelago for the occurrence of humpback whale song during the 2019-2020 breeding season. Relative song prevalence was established using a machine learning tool and by quantifying the level of song chorusing. A generalized additive model framework was applied to understand the associations between habitat variables and humpback whale song occurrence, and sound propagation modeling was performed to examine whether acoustic propagation influenced observed patterns. Whale song was recorded at all monitored and surveyed locations across the archipelago, albeit in varying amounts. Among the locations monitored with moored recorders, the highest and most sustained seasonal chorusing levels were measured off Maui followed by French Frigate Shoals (Kānemilohai), Hawaii Island, Middle Bank, Oahu, Kauai, Gardner Pinnacles (Pūhāhonu) and Pearl and Hermes Reef (Holoikauaua), respectively. The Wave Glider mission to PMNM revealed that song prevalence was highest at Middle Bank and gradually decreased further to the northwest, reaching a minimum at Gardner Pinnacles (Pūhāhonu). However, song occurrence increased again at Raita Bank, remaining high between Raita Bank and the Northampton Seamounts. The results reveal that nearly the entire Hawaiian archipelago is exploited by humpback whales during the winter and early spring months. Moreover, song occurrence patterns suggest that there may be more structure in the distribution of whales in PMNM than previously known and raises questions about whether multiple subpopulations occur across the archipelago.

Ocean gliders equipped with acoustic telemetry receivers offer a promising approach for studying the movement of marine fishes, yet most surveys to date have been brief and rarely include direct comparisons with traditional stationary tracking methods. To evaluate glider-based tracking, a Wave Glider unmanned surface vehicle (USV) was deployed on eight multi-week missions over the east Florida continental shelf. The survey aimed to systematically detect acoustically tagged animals and compare glider performance to a contemporaneous stationary tracking array, with range tests conducted using two receiver types mounted on the glider. Across 190 days and 9,600 km of survey effort, the Wave Glider recorded 331 animal encounters representing 20 species, with blacktip shark ( Carcharhinus limbatus ), blacknose shark ( C. acronotus ), and red drum ( Sciaenops ocellatus ) among the most frequently detected. Detection range trials yielded 50% detection probabilities at distances up to 350 m. Boosted regression tree models indicated that distance between tag and receiver explained 57–71% of the variance in detection probability, with ocean currents, wave height, and solar irradiance also contributing. Compared to a 62-receiver stationary array, the Wave Glider detected, on average, 64% of the species and 40% of the tagged animals, but less than 2% of the detections over identical timeframes. Further, animal encounters with the glider lasted only 14 minutes on average, versus 48 minutes for stationary receivers. Nonetheless, the glider performed comparably on a per-receiver basis, yielding similar numbers of encounters, animals, and species. Moreover, the Wave Glider successfully navigated complex bathymetry surrounding offshore sand shoals, relocated several shed tags, and paired encounters with a variety of oceanographic and meteorological measurements. These results confirm that USVs are suitable for systematic coastal fish tracking. While single gliders cannot replace stationary arrays in most situations, they are realistic solutions for relocating animals in remote locations, monitoring dispersal across discrete habitat patches (e.g., reefs, wind turbines), and providing highly localized habitat context.

Formed by humidity stratification in the marine atmospheric boundary layer, evaporation ducts serve as critical natural channels for maritime over-the-horizon (OTH) wireless communication. Their unique structure effectively confines electromagnetic (EM) wave propagation, substantially enhancing the link stability and transmission quality of long-range maritime communication while exerting notable impact on OTH EM wave propagation. Tropical cyclones profoundly alter near-surface meteorological conditions and disrupt the distribution uniformity of evaporation ducts, directly inducing fluctuations in communication link path loss (PL), intensified signal attenuation, and even short-term outages, severely impairing maritime broadband communication. However, direct and mobile observations of evaporation ducts within typhoon interiors remain limited. This study investigated the evolution of evaporation duct height (EDH) during Typhoon Koinu (202314) through analysis of 108 hours of continuous observations by three clustered wave gliders. One glider traversed the typhoon eye, while the other two monitored regions of high wind speed (WS). The maximum recorded WS reached 26.5 m/s, accompanied by EDH of 11.9 m, whereas within the eye region, WS was 4.36 m/s with EDH of 5.7 m. The presence of the typhoon’s eye caused a 6.2-m reduction in EDH. Relative humidity (RH) fluctuated from 70% to 95% before the typhoon’s arrival and remained at around 90% during the typhoon’s passage. Correlation analysis indicated that RH was the dominant factor influencing EDH before the typhoon’s arrival, showing negative correlation (Spearman correlation coefficient: −0.83). In contrast, WS was the main driver of EDH variation during the typhoon’s passage, exhibiting strong positive correlation (Spearman correlation coefficient: 0.82). Sensitivity analysis confirmed that the inhibitory effect of elevated RH outweighed the contribution of high WS to EDH enhancement, leading to lower EDH values during the passage of the typhoon than in the pre-typhoon period. Analysis of the spatial distribution of EM wave propagation indicated that the low EDH induced by low WS in the typhoon’s eye caused PL that was 24 dB greater than under high-WS scenarios; overall, the presence of the typhoon’s eye caused greater PL.

Over the last several years, the Air-Sea Interaction Laboratory at Scripps Institution of Oceanography has developed a fleet of wave-powered, uncrewed Wave Gliders (Liquid Robotics) specifically designed and instrumented for state-of-the-art air-sea interaction and upper ocean observations. In this study, measurement capabilities from these platforms are carefully described, compared, and validated against coincident measurements from well-established, independent data sources. Data collected from four major field programs from 2013 to 2020 are considered in the analysis. Case studies focusing on air-sea interaction, Langmuir circulations, and frontal processes are presented. We demonstrate here that these novel, instrumented platforms are capable of collecting observations with minimal flow-structure interaction in the air-sea boundary layer, a region of crucial current and future importance for models of weather and climate.