Ice Production Research Articles

Varietal effects on Greenhouse Gas emissions from rice production systems under different water management in the Vietnamese Mekong Delta

AbstractRice production accounts for 15% of the national Greenhouse Gas (GHG) emissions and Vietnam aims at reducing emissions from rice production by focusing on changing farming practices. However, the potential for mitigation through the selection of different rice varieties is still poorly understood. A two‐year field screening of 20 rice varieties under continuous flooding (CF) and alternate wetting and drying (AWD) irrigation was conducted in the Vietnamese Mekong Delta (VMD), Vietnam, employing the closed chamber method for assessing GHG emissions. The results confirmed that varietal variation was the largest for methane (CH4) emissions under CF. Across the varietal spectrum, CH4 emissions were more important than nitrous oxide (N2O) (accounts for less than 2% of the CO2e) with the lowest emitting variety showing 243 kg CH4 ha−1 and the highest emitting variety showing 398 kg CH4 ha−1 emissions as compared to 0.07 kg N2O ha−1 and 0.76 kg N2O ha−1 emissions, respectively. Under AWD, CH4 emissions were generally strongly reduced with the varietal effect being of minor importance. Compared with IPCC default values, the data set from the two seasons yielded higher Emission Factors (EFs) under CF (2.92 and 3.00 kg ha−1 day−1) as well as lower Scaling Factors (SFs) of AWD (0.41 and 0.38). In the context of future mitigation programs in the VMD, the dry season allows good control of the water table, so varietal selection could maximize the mitigation effect of AWD that is either newly introduced or practised in some locations already. In the wet seasons, AWD may be difficult to implement whereas other mitigation options could be implemented such as selecting low‐emitting cultivars.

Biomarker Records of Environmental Shifts on the Labrador Shelf During the Holocene

AbstractThe ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.

Discriminant analysis of the freeze-up and break-up conditions in the Inner Mongolia Reach of the Yellow River

Abstract This study divided the total storage potential in a natural channel into the ice production volume and the water storage capacity volume. Thermal factors, hydraulic processes, topography, and ice formation were selected to derive a discriminant equation for freeze-up and break-up conditions in the Inner Mongolia Reach of the Yellow River. The trends observed from data for the freeze-up dates, break-up dates, and total frozen days from 2017 to 2020 conform to the principle that the river is gradually frozen from the downstream to the upstream and later thawed from the upstream to the downstream. The number of frozen days in the downstream is greater than in the upstream. Results indicate that freeze-up typically occurs when the proportion of ice in the channel is relatively high. Higher temperatures and greater discharges are required to facilitate the break-up of the river when the equilibrium ice thickness is greater. This study can provide a theoretical basis and framework for establishing an accurate freeze-up and break-up forecast model to prevent and mitigate ice-induced disasters.

Оптимизации режимов работы судовой холодильной установки с аккумулятором искусственного холода

The ways of optimizing the operation of a refrigeration unit for fishing and refrigerated vessels with the additional inclusion of artificial cold storage devices are investigated. For this purpose, a new technology of cold storage has been developed on the basis of a refrigerating machine with direct contact between media and ice production. The refrigerant RC318 was taken as freon which does not form crystalline hydrates. Based on this, the optimization of the operation of a single-stage refrigeration machine was carried out using the Lagrange multiplier method for the target function of energy consumption, calculated by reducing the exergy flow in the system. The data obtained show the relevance and prospects of using cold accumulation on ships to reduce energy costs for the operation of refrigeration equipment and increase the autonomy of fishing vessels. Optimization according to the given method leads to two modes of operation of the refrigerating machine, as the most optimally beneficial in terms of operating conditions during the generation of cold. Optimization was carried out for two schemes for including a cold accumulator in the cold supply system. The proposed optimization methods make it possible to reduce the energy consumption of refrigeration units to the level of design loads, and to compensate for peak loads with the help of cold from batteries. Further research in this matter is aimed at reducing the size of the battery, increasing its energy efficiency and developing recommendations for inclusion in the general schemes of ship refrigeration plants based on mathematical optimization models and field experiments. It also plans to further improve the methods of cold accumulation based on ice generation with direct contact of media inside refrigeration units.

Reconstruct the AMSR-E/2 thin ice thickness algorithm to create a long-term time series of sea-ice production in Antarctic coastal polynyas

This study presented an extended time series of ice production in Antarctic coastal polynyas for 20 years of 2002–21 using high spatial resolution satellite data from passive microwave sensors: the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and the Advanced Microwave Scanning Radiometer 2 (AMSR2). For this, we reconstructed the previously presented thin ice thickness algorithms and re-estimated ice production by replacing atmospheric input data for the heat flux calculations with the newly released ECMWF Reanalysis v5 (ERA5). The consistency of ice production between AMSR-E and AMSR2, whose operation periods do not overlap, was confirmed from comparisons with ice production by the Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager Sounder (SSMIS) with relatively coarse spatial resolution. The open ocean area, which cannot be detected from the thin ice thickness algorithm, was defined using sea-ice concentration (SIC) from AMSR-E and AMSR2. The satellite derived SIC has been suggested to be underestimated in the new thin ice (polynya) area. The effect of the underestimation on the ice production estimation was evaluated. The underestimation of SIC from three major algorithms was also investigated from comparisons with the thin ice thickness presented in this study. The coastal polynya dataset covering 20 years with the higher spatial resolution presented in this study is vital for climate-change-related studies.

The Impact of Solar Radiation at Different Colombian Thermal Floors on an Adsorption Refrigeration Cycle

The process of energy transition in Colombia has sparked an exploration into appropriate geographical areas for the utilization of solar energy. The country’s rugged terrain and significant climate variability pose challenges for implementing standardized technologies uniformly across all regions. Consequently, this study aims to develop and apply a mathematical model to characterize the performance of a solar adsorption cooling system under the environmental conditions found in six distinct Colombian cities, taking into account different thermal profiles and extreme weather periods such as the El Niño and La Niña phenomena. The selected mathematical model was simulated in these cities, considering ambient temperature and solar radiation variables over a twelve-month period during these extreme weather phenomena and an additional twelve-month period representative of a typical year with minimal influence from these phenomena. The results indicated that despite a lower coefficient of performance (COP) compared to the other cities, Riohacha demonstrated a greater number of ice production days owing to its high levels of solar radiation.

A bin microphysics parcel model investigation of secondary ice formation in an idealised shallow convective cloud

Abstract. We provide the first systematic study of ice formation in idealised shallow clouds from collisions of supercooled water drops with ice particles (mode 2). Using the University of Manchester bin microphysics parcel model, we investigated the sensitivity of ice formation due to mode 2 for a wide range of parameters, including aerosol particle size distribution, updraft speed, cloud-base temperature, cloud depth, ice-nucleating particle concentration, and freezing fraction of mode 2. We provide context to our results with other secondary ice production mechanisms as single mechanisms and combinations (rime splintering, spherical freezing fragmentation of drops (mode 1), and ice–ice collisions). There was a significant sensitivity to aerosol particle size distribution when updraft speeds were low (0.5 m s−1); secondary ice formation did not occur when the aerosol particle size distribution mimicked polluted environments. Where secondary ice formation did occur in simulated clouds, significant ice formation in the shallower clouds (1.3 km deep) was due to mode 2 or a combination which included mode 2. The deeper clouds (2.4 km deep) also had significant contributions from rime splintering or ice–ice collisional breakup secondary ice production (SIP) mechanisms. While simulations with cloud-base temperatures of 7 ∘C were relatively insensitive to ice-nucleating particle concentrations, there was a sensitivity in simulations with cloud-base temperatures of 0 ∘C. Increasing the ice-nucleating particle concentration delayed ice formation. Our results suggest that collisions of supercooled water drops with ice particles may be a significant ice formation mechanism within shallow convective clouds where rime splintering is not active.

Arctic Cloud‐Base Ice Precipitation Properties Retrieved Using Bayesian Inference

AbstractCloud‐climate feedbacks are still the greatest source of uncertainty in current climate projections. Arctic clouds, which are predominantly stratiform and supercooled, often long‐lived, and nearly continuously precipitate ice particles, contribute roughly 10% of the uncertainty attributed to the global cloud feedback. This Arctic cloud uncertainty is driven by incomplete observational and theoretical knowledge required to estimate and explain the state and active processes occurring in those clouds. A focus on ice precipitation properties at Arctic cloud base rather than the surface deconfounds the product of cloud condensate sink processes from the influence of the atmospheric thermodynamic state below cloud base, rendering cloud‐base properties a more appealing target for inference and evaluation of model simulations. Here I describe an inverse model for the estimation of cloud base ice precipitation properties over Utqiagvik, North Slope of Alaska, using the synthesis of ground‐based radar and lidar measurements. By leveraging a Markov Chain Monte Carlo algorithm as the core of the inverse model, a wide range of particle size distributions are sampled, and different combinations of ice habit models are examined, both of which are typically fixed in other retrieval methods. Results show intriguing links between different cloud base thermodynamic and ice precipitation properties. Apparent ice number concentration enhancements at temperatures of −5 and −15°C suggest possible secondary ice production (SIP). The analysis alludes to an overestimation of SIP occurrence and intensity, especially in studies relying only on radar or lidar measurements. Finally, reflectivity‐dependent ice precipitation rate and ice water content parameterizations are presented.

Effects from Time Dependence of Ice Nucleus Activity for Contrasting Cloud Types

Abstract The role of time-dependent freezing of ice nucleating particles (INPs) is evaluated with the “Aerosol–Cloud” (AC) model in 1) deep convection observed over Oklahoma during the Midlatitude Continental Convective Cloud Experiment (MC3E), 2) orographic clouds observed over North California during the Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX), and 3) supercooled, stratiform clouds over the United Kingdom, observed during the Aerosol Properties, Processes And Influences on the Earth’s climate (APPRAISE) campaign. AC uses the dynamical core of the WRF Model and has hybrid bin–bulk microphysics and a 3D mesoscale domain. AC is validated against coincident aircraft, ground-based, and satellite observations for all three cases. Filtered concentrations of ice (>0.1–0.2 mm) agree with those observed at all sampled levels. AC predicts the INP activity of various types of aerosol particles with an empirical parameterization (EP), which follows a singular approach (no time dependence). Here, the EP is modified to represent time-dependent INP activity by a purely empirical approach, using our published laboratory observations of time-dependent INP activity. In all simulated clouds, the inclusion of time dependence increases the predicted INP activity of mineral dust particles by 0.5–1 order of magnitude. However, there is little impact on the cloud glaciation because the total ice is mostly (80%–90%) from secondary ice production (SIP) at levels warmer than about −36°C. The Hallett–Mossop process and fragmentation in ice–ice collisions together initiate about 70% of the total ice, whereas fragmentation during both raindrop freezing and sublimation contributes <10%. Overall, total ice concentrations and SIP are unaffected by time-dependent INP activity. In the simulated APPRAISE case, the main causes of persistence of long-lived clouds and precipitation are predicted to be SIP in weak embedded convection and reactivation following recirculation of dust particles in supercooled layer cloud.

Effect of Dual-frequency ultrasonic on subcooled water freezing

Ultrasonic-assisted freezing has received much attention for its outstanding capability to improve freezing performance. However, most researchers focus only on single-frequency ultrasound, lacking research on dual-frequency or multi-frequency ultrasound. Based on the relevant theory of the promotion of solution crystallization by ultrasound wave, this paper experimentally studied the subcooling degree and time of water freezing under the action of ultrasound. The experimental study was carried out on the production of ice from water by using different ultrasonic waves under a specific power. The results show that the effect of ultrasound with specific frequency combinations can improve the speed of water freezing and reduce the subcooling degree. When the experimental conditions are 28+33 kHz and 60 W, the comprehensive performance is the best. Compared with the condition without ultrasound, the subcooling degree is reduced by 5.28 K, and the time required for the complete solidification of water into ice was reduced by a duration of 60 s.

Investigating the vertical extent and short-wave radiative effects of the ice phase in Arctic summertime low-level clouds

Abstract. Low-level (cloud tops below 2 km) mixed-phase clouds are important in amplifying warming in the Arctic region through positive feedback in cloud fraction, water content and phase. In order to understand the cloud feedbacks in the Arctic region, good knowledge of the vertical distribution of the cloud water content, particle size and phase is required. Here we investigate the vertical extent of the cloud-phase and ice-phase optical properties in six case studies measured in the European Arctic during the ACLOUD campaign. Late spring- and summertime stratiform clouds were sampled in situ over pack ice, marginal sea ice zone and open-ocean surface, with cloud top temperatures varying between −15 and −1.5 ∘C. The results show that, although the liquid phase dominates the upper parts of the clouds, the ice phase was frequently observed in the lower parts down to cloud top temperatures as warm as −3.8 ∘C. In the studied vertical cloud profiles, the maximum of average liquid phase microphysical properties, droplet number concentration, effective radius and liquid water content, varied between 23 and 152 cm−3, 19 and 26 µm, 0.09 and 0.63 g m−3, respectively. The maximum of average ice-phase microphysical properties varied between 0.1 and 57 L−1 for the ice number concentration, 40 and 70 µm for the effective radius, and 0.005 and 0.08 g m−3 for the ice water content. The elevated ice crystal number concentrations and ice water paths observed for clouds, with cloud top temperatures between −3.8 and −8.7 ∘C can be likely attributed to secondary ice production through rime splintering. Low asymmetry parameters between 0.69 and 0.76 were measured for the mixed-phase ice crystals with a mean value of 0.72. The effect of the ice-phase optical properties on the radiative transfer calculations was investigated for the four cloud cases potentially affected by secondary ice production. Generally the choice of ice-phase optical properties only has a minor effect on the cloud transmissivity and albedo, except in a case where the ice phase dominated the upper cloud layer extinction. In this case, cloud albedo at solar wavelengths was increased by 10 % when the ice phase was given its measured optical properties instead of treating it as liquid phase. The presented results highlight the importance of accurate vertical information on cloud phase for radiative transfer and provide a suitable data set for testing microphysical parameterizations in models.

Astrochemical models of interstellar ices: History matters

Context. Ice is ubiquitous in the interstellar medium. As soon as it becomes slightly opaque in the visible, it can be seen for visual extinctions (AV) above ~1.5. The James Webb Space Telescope (JWST) will observe the ice composition toward hundreds of lines of sight, covering a broad range of physical conditions in these extinct regions. Aims. We model the formation of the main constituents of interstellar ices, including H2O, CO2, CO, and CH3OH. We strive to understand what physical or chemical parameters influence the final composition of the ice and how they benchmark to what has already been observed, with the aim of applying these models to the preparation and analysis of JWST observations. Methods. We used the Nautilus gas-grain model, which computes the gas and ice composition as a function of time for a set of physical conditions, starting from an initial gas phase composition. All important processes (gas-phase reactions, gas-grain interactions, and grain surface processes) are included and solved with the rate equation approximation. Results. We first ran an astrochemical code for fixed conditions of temperature and density mapped in the cold core L429-C to benchmark the chemistry. One key parameter was revealed to be the dust temperature. When the dust temperature is higher than 12 K, CO2 will form efficiently at the expense of H2O, while at temperatures below 12 K, it will not form. Whatever hypothesis we assumed for the chemistry (within realistic conditions), the static simulations failed to reproduce the observed trends of interstellar ices in our target core. In a second step, we simulated the chemical evolution of parcels of gas undergoing different physical and chemical situations throughout the molecular cloud evolution and starting a few 107 yr prior to the core formation (dynamical simulations). We obtained a large sample of possible ice compositions. The ratio of the different ice components seems to be approximately constant for AV > 5, and in good agreement with the observations. Interestingly, we find that grain temperature and low AV conditions significantly affect the production of ice, especially for CO2, which shows the highest variability. Conclusions. Our dynamical simulations satisfactorily reproduce the main trends already observed for interstellar ices. Moreover, we predict that the apparent constant ratio of CO2/H2O observed to date is probably not true for regions of low AV, and that the history of the evolution of clouds plays an essential role, even prior to their formation.

Regenerator performance using freezing concentration for heat source tower heat pump system

Freeze concentration has a good regeneration effect and is easy for latent heat utilization. The electronic expansion valve opening has a great impact on the icing process. Hence, to investigate variations in the freezing process and gain the optimum regeneration effect, a solution regenerator was tested under different system-side control strategies. The solution volume flow was 5 m3/h and the electronic expansion valve opening degree (OEEV) was from 100% to 50%. For ice-covering growth, ice in low opening degree spent a long time to cover the plate. The area of ice under 100% to 65% OEEV was 1.43 times that under 50% OEEV. Peak velocities from 100% to 50% OEEV all appeared in the early stage of icing development. Moreover, the low opening degree made the ice distribute unevenness. The percentage slope of 100% OEEV was 1.23% and that of 50% OEEV was 3.46%. In addition, decreasing ice thickness uniformity was beneficial to the separation process. The separation ratio from 100% to 50% OEEV was 49.51%, 51.67%, 57.88%, and 74.54%, respectively. Both the low average thickness growth rate and high separation ratio were beneficial to increase the regeneration concentration. The effective specific ice production rate was from 100% to 50% OEEV was 5.99 kg/kWh, 6.18 kg/kWh, 6.94 kg/kWh, and 6.88 kg/kWh, respectively. Results showed that 65% OEEV operation was optimum for the solution regenerator unit using freeze concentration.

Lattice Boltzmann model for predicting frosting process on surfaces considering wettability.

The process of frosting is a multiscale problem, which leads to challenges of proposing accurate numerical methods. In this study, a lattice Boltzmann model for predicting frost formation and growth on surfaces of various wettabilities is proposed based on the heterogeneous nucleation and dendrite growth theories. Three lattice Boltzmann equations are used to calculate the velocity, humidity, and temperature distributions. Furthermore, the heterogeneous nucleation theory and dendrite growth theory are used to construct the equations that govern ice production during the frosting process, so that the surface wettability can be considered. After experimental validation, the model was used in the analysis of frosting behaviors on plates and in microchannels with different wettabilities. The effects of the intrinsic contact angles and roughness on the frost layer properties were evaluated. This study will likely facilitate a better understanding of frosting on the mesoscopic level.

Slowdown of Antarctic Bottom Water export driven by climatic wind and sea-ice changes

Antarctic Bottom Water (AABW) is pivotal for oceanic heat and carbon sequestrations on multidecadal to millennial timescales. The Weddell Sea contributes nearly a half of global AABW through Weddell Sea Deep Water and denser underlying Weddell Sea Bottom Water that form on the continental shelves via sea-ice production. Here we report an observed 30% reduction of Weddell Sea Bottom Water volume since 1992, with the largest decrease in the densest classes. This is probably driven by a multidecadal reduction in dense-water production over southern continental shelf associated with a >40% decline in the sea-ice formation rate. The ice production decrease is driven by northerly wind trend, related to a phase transition of the Interdecadal Pacific Oscillation since the early 1990s, superposed by Amundsen Sea Low intrinsic variability. These results reveal key influences on exported AABW to the Atlantic abyss and their sensitivity to large-scale, multidecadal climate variability.

The application of freezing technology for zinc removal from Faro pit mine-impacted water, Yukon, Canada

The application of freezing technology (cryopurification) could be a viable water treatment solution to the environmental industry, especially in northern climates as it holds several advantages, including high energy efficiency, the absence of chemical pre-treatment and cost-efficiency. The use of cryopurificiation in Northern Canada is of interest, considering three of the five largest federal contaminated mine sites where water treatment is typically required are located within Yukon and Northwest Territories. The current research aims to address the problem of elevated zinc concentrations in mine-impacted water (Faro Mine, Yukon, Canada) by applying cryopurification. The paper scope includes laboratory testing to quantitatively describe zinc removal from Faro Mine's water using cryopurification under various initial and boundary conditions. Based on laboratory testing results, zinc could be removed with an efficiency of above 75% and 95% using single-stage freezing under no mixing and constant mixing conditions, respectively and up to 97% in freezing-melting tests. The results reveal the purest ice production at freezing temperature range from −0.5 to −5 °C. Ice is purer with each subsequent melt fraction according to the results of freezing-melting laboratory tests. The addition of seed ice crystals enhances the purity of ice up to 10–14% and ice block shape has an effect on the purification process, as the results of laboratory testing show. The effect of mixing shows 23–72% improvement in overall removal efficiency depending on freezing temperature. The outcomes of current research form a foundation toward the development of an exceptional water treatment process utilizing northern climates' cold temperature conditions and having a potential to be scaled up.

Understanding the Physical Forcings Behind the Biogeochemical Productivity of the Hudson Bay Complex

AbstractMultiple factors influence the spatial and temporal chlorophyll‐a concentration of marine systems. The Hudson Bay Complex has historically been seen as a large, low‐production inland sea situated in the north of Canada. However, recent field campaigns, for the BaySys project, have provided new data on primary production in the bay. Due to the Hudson Bay complex's positioning, it experiences seasonal sea‐ice cover and has many rivers draining into it, resulting in a unique estuarine‐like environment. We use the biogeochemical model BLINGv0 + DIC, coupled to the online regional physical oceanographic and sea‐ice models, NEMOv3.6 and LIM2, respectively, forced with two bias‐corrected Coupled Model Intercomparison Project 5 climate forcings (MIROC5 and MRI) to simulate the base of the ecosystem. The simulations were evaluated with chlorophyll‐a satellite imagery and observations collected in 2018 and analyzed with Empirical Orthogonal Functions to understand the underlying physical forcings and key areas of chlorophyll‐a concentration distribution. The evaluation showed that both simulations successfully reproduced the sea‐ice melt, from west to east and formation, from north to south and correlated well with spatial bloom patterns. The main drivers of phytoplankton growth are the seasonal light and nutrient levels (48% and 54%), the mixed layer depth dynamics (18% and 14%), nutrient supply from rivers (13% and 8%), and sea ice production (7%) for the MIROC5 and MRI simulations, respectively. The sea‐ice dynamics and river runoff played a significant role in the system's productivity. Therefore, with future climate change and increased river regulation projects, up to 20% of overall chlorophyll‐a may be negatively impacted.

Modelling the Impact of Secondary Ice Production on the Charge Structure of a Mesoscale Convective System

Modelling the Impact of Secondary Ice Production on the Charge Structure of a Mesoscale Convective System

Evaluation of Microbial Quality of Fishes and Sanitary Condition of Wholesale and Retail Fish Markets in Peri-urban Area of Kolkata, India

The present study conducted during October, 2019 to January, 2020 was aimed to assess the microbial quality of selected fish species viz., Labeo rohita, Lates calcarifer and Johnius belangeri and check the sanitary condition of two selected fish markets i.e., Baghajatin wholesale fish market and Garia retail fish market in Kolkata, India. The results of TPC of fish muscle never crossed the limit of 4.70 log cfu g-1 as specified by ICMSF. Total plate count (TPC) of fish muscle were well within the limit of acceptability suggesting to be fit for consumption. The Total plate count value of water, ice, and swab samples were found higher in the month of October and lower in the month of January. The high values of TPC were recorded in water, ice and swab samples suggesting poor sanitation, improper handling and use of contaminated water in ice production. All the three species collected from two different selected fish markets were detected to contain the pathogenic microorganisms like Salmonella sp., Clostridium sp., Listeria sp. and Staphylococcus aureus. The results also indicated the presence of faecal coliform in water, ice and swab samples. It is recommended that potable water must be used for manufacturing of ice and handling should be done under good hygiene and sanitary conditions.

Spatial characteristics of frazil streaks in the Terra Nova Bay Polynya from high-resolution visible satellite imagery

Abstract. Coastal polynyas around the Antarctic continent are regions of very strong ocean–atmosphere heat and moisture exchange that are important for local and regional weather, sea ice production, and water mass formation. Due to extreme atmospheric conditions (very strong offshore winds, low air temperature, as well as humidity) the surface ocean layer in polynyas is highly turbulent, with mixing due to combined Langmuir, wind-induced, and buoyancy-driven turbulence. One of the visible signs of complex interactions between the mixed-layer dynamics and the forming sea ice are frazil streaks, elongated patches of high ice concentration separated by areas of open water. In spite of their ubiquity, observational and modelling analyses of frazil streaks have been very limited largely due to the fact that their significance for heat flux and ice production is only just becoming apparent. In this study, the first comprehensive analysis of the spatial variability of surface frazil concentration is performed for the Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in high-resolution (pixel size 10–15 m) visible satellite imagery, and their properties (surface area, width, spacing, and orientation) are linked to the meteorological forcing (wind speed and air temperature). This provides a simple statistical tool for estimating the extent and ice coverage of the region of high ice production under given meteorological conditions. It is also shown that the orientation of narrow streaks tends to agree with the wind direction, suggesting the dominating role of the local wind forcing in their formation. Very wide streaks, in turn, deviate from that pattern, as they are presumably influenced by several additional factors, including local water circulation and the associated convergence zones. An analysis of peak wavelengths and directions determined from the images, compared to analogous open-water wavelengths computed with a spectral wave model, demonstrates a significant slow-down in the observed wave growth in TNBP. This suggests an important role of frazil streaks in modifying wind-wave growth and/or dissipation in polynyas.