Observation of wave propagation over 1,000 km into Antarctica winter pack ice

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 L\"utzow-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 measurement duration reached 333 days. During the winter months, it was located deep in the ice cover with the shortest distance to the ice-free Southern Ocean over 1,000 km; at this time, there was evidence of ocean wave signals at the buoy position. Using the directional wave spectra obtained from the ECMWF's reanalysis, we show that the Medusa-766 observed waves were likely generated by an extratropical cyclone in the Southern Ocean. Wave-induced ice breakup potential for such an event could extend 100s km into the ice field. When Medusa-766 was in LHB in the summer months, it did not detect sizeable wave energy despite the low sea ice concentration extent even during on-ice waves events. Characterising the considerable differences in the wave attenuation at LHB is needed to elucidate the relative contribution of ocean waves to the unstable LHB fast ice. The success of Medusa-766 demonstrates the robustness of the general design, hardware, firmware, and the high sensitivity of the sensor used. The result is promising for future LHB wave-ice interaction research

An affordable and customizable wave buoy for the study of wave-ice interactions: design concept and results from field deployments

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-source instruments optimized for deployment on ice floes, their customizability and survivability remain limited, especially in open waters. This study presents a novel design concept for an affordable and customizable wave buoy, aimed for wave measurements in marginal ice zones. The central focus of this wave buoy design is the application of 3D printing as rapid prototyping technology. By utilizing the high customizability offered by 3D printing, the previously developed solar-powered wave buoy was customized to install a battery pack to continue the measurements in the high latitudes for more than several months. Preliminary results from field deployments in the Pacific and Arctic Oceans demonstrate that the performance of the instruments is promising. The accuracy of frequency wave spectra measurements is found to be comparable to that of considerably more expensive instruments. Finally, the study concludes with a general evaluation of using rapid prototyping technologies for buoy designs and proposes recommendations for future designs

Observation of anomalous spectral downshifting of waves in the Okhotsk Sea Marginal Ice Zone

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 imaging system and Inertial Measurement Unit. Sea ice was observed visually and by aerial photographs by drone, while satellite synthetic aperture radar provided basin-wide spatial distribution. On 12 February, a swell system propagating from east northeast was detected by both the stereo imaging system and the buoy-on-ice. The wave system attenuated from 0.34 m significant wave height to 0.25 m in about 90 km, while the wave period increased from 10 s to 15–17 s. This anomalous spectral downshifting was not reproduced by numerical hindcast and by applying conventional frequency-dependent exponential attenuation to the incoming frequency spectrum. The estimated rate of spectral downshifting, defined as a ratio of momentum and energy losses, was close to that of uni-directional wave evolution accompanied by breaking dissipation: this indicates that dissipation-driven nonlinear downshifting may be at work for waves propagating in ice

Estimating the elastic modulus of landfast ice from wave observations

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 landfast sea ice. From observations of low-frequency dispersive waves, we obtain an estimate of the effective elastic modulus in the range of 0.4–0.7 GPa. This is lower than the purely elastic modulus of the ice estimated at 1 GPa as derived from in situ beam experiments. Importantly, our experimental observation is significantly lower than the default value currently in use in wave models. While our estimate is not representative for all sea ice, it does indicate that considerably more measurements are required to provide confidence in the development of parameterizations for this complex sea-ice property for wave models

Comparison of alterations in cerebral hemoglobin oxygenation in late life depression ans Alzheimer's disease as assessed by near-infrared spectroscopy

BACKGROUND: Patients with Alzheimer's disease (AD) often present with apathy symptoms resembling the decreased motivation observed in depressed patients. Therefore, differentiating the initial phase of AD from late life depression may be difficult in some cases. Near-infrared spectroscopy (NIRS) is a functional neuroimaging modality that uses near-infrared light to measure changes in hemoglobin concentration on the cortical surface during activation tasks. The objective of this study was to investigate differences in brain activation associated with late life depression and with AD by means of NIRS. METHODS: NIRS was performed in 30 patients with depression, 28 patients with AD, and 33 healthy controls, all aged 60 years or older. During two tasks, a verbal fluency task and a visuospatial task, changes in oxygenated hemoglobin concentration in the frontal and parietal cortices were investigated. RESULTS: In the visuospatial task, cortical activation was lower in the depressed group than in the AD group, and significant differences were observed in the parietal cortex. CONCLUSIONS: NIRS can detect differences in brain activation between patients with late life depression and those with AD. NIRS is a promising tool for the differential diagnosis of late life depression and AD.ArticleBEHAVIORAL AND BRAIN FUNCTIONS. 10:8 (2014)journal articl

A dataset of direct observations of sea ice drift and waves in ice

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 sea ice drift and waves in ice. A total of 15 deployments were performed over a period of 5 years in both the Arctic and Antarctic, involving 72 instruments. These provide both GPS drift tracks, and measurements of waves in ice. The data can, in turn, be used for tuning sea ice drift models, investigating waves damping by sea ice, and helping calibrate other sea ice measurement techniques, such as satellite based observations

Five-member ensemble wave forecast for the R/V Mirai 2023 Arctic Ocean expedition using different sea ice forcing

The 14th Symposium on Polar Science/Interdisciplinary sessions [IA] Arctic Research, Thu. 16 Nov. / 2F Auditorium, National Institute of Polar Researc

Spectral downshift of Three-wave system and Bichromatic waves under “sea ice”

The 14th Symposium on Polar Science/Interdisciplinary sessions [IA] Arctic Research, Thu. 16 Nov. / 2F Auditorium, National Institute of Polar Researc

Raw data of sea ice inertial motion recorded by 15 OpenMetBuoys in the marginal ice zone north of Svalbard in 2022

A total of 15 OpenMetBuoys (OMBs) were deployed in the marginal ice zone northwest of Svalbard (array of 14 buoys) and on the fast ice off Greenland (one buoy) as part of RV Polarstern expedition PS131 (ATWAICE) in July - August 2022. The OMBs, also referred to as wave buoys, reported GPS position and wave spectra from 20-minute inertial motion averages at hourly intervals via the iridium satellite network. From these, significant wave height and peak wave period can be calculated. Two of the buoys ceased transmission within days of the deployment, while all other buoys recorded data for several weeks/months. The buoys were deployed on ice floes of various dimensions ranging from 15 m to as large as ~2km. The attached .zip archive contains a netcdf file incorporating all buoy data, several python scripts to read and process the data, as well as selected preliminary data quicklooks. The buoys were build and deployed as a collaboration between the Alfred-Wegener-Institute, the University of Tokyo, and the Norwegian Meteorological Institute

A comparison of an operational wave–ice model product and drifting wave buoy observation in the central Arctic Ocean: investigating the effect of sea-ice forcing in thin ice cover

A prototype OpenMetBuoy (OMB) was deployed alongside a commercial buoy in the central Arctic Ocean, north of the Laptev Sea, where there are historically no wave observations available. The inter-buoy comparison showed that the OMB measured wave heights and periods accurately, so the buoy data were used to study the predictability of a wave–ice model. The first event we studied was when both buoys observed a sudden decrease in significant wave heights Hm0, which was caused by the change of wind directions from along the ice edge to off-ice wind. The Arctic Ocean Wave Analysis and Forecast wave–ice model product (ARC MFC) underestimated the Hm0 on the account of the fetch being constrained by the inaccurate model representation of an ice tongue. The second case was an on-ice wave event as new ice formed. In this instance, the ARC MFC wave–ice model product largely underestimated the downwind buoy Hm0. Model sea-ice conditions were examined by comparing the ARC MFC sea-ice forcing with the neXtSIM sea-ice model product, and our analysis revealed the ARC MFC did not resolve thin ice thickness distribution for ice types like young and grey ice, typically less than 30 cm. The ARC MFC model’s wave dissipation rate has a sea-ice thickness dependence and overestimated wave dissipation in thin ice cover; sea-ice forcing that can resolve the thin thickness distribution is needed to improve the predictability. This study provides an observational insight into better predictions of waves in marginal ice zones when new ice forms