Interfacial generation of internal waves and turbulent heat flux due to enhanced inertial motion for deformed sea-ice floe: Preliminary results from MOSAiC expedition

2021 ◽  
Author(s):  
Yusuke Kawaguchi ◽  
Zoe Koenig ◽  
Mario Hoppman ◽  
Daiki Nomura ◽  
Mats Granskog ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Sea Ice ◽  
Internal Waves ◽  
Inertial Motion ◽  
Eddy Heat Flux ◽  
Ice Drift ◽  
Ice Floes ◽  
Ocean Boundary ◽  
Perennial Ice

<p>Sea-ice drift becomes most energetic at last moment in summer when refreezing is about to onset. Perennial ice floes, surviving over all seasons, tend to experience a number of deformation events over yearlong drift, with uneven distribution in thickness. Deformed ice floes protrude tall keels into water of ice-ocean boundary, and then stir it up. Consequently, combination of fast ice drift and deformation-experienced perennial ice could be a primary source of momentum/thermal energy for upper waters through propagation of internal waves. In this study, during MOSAiC expedition, we attempted to perform direct observation of wave generation in ice-ocean boundary layer underneath a drifting ice floe in the central Arctic Ocean. Time series of turbulent signals, represented by Reynolds stress <u'w'> and eddy heat flux <w'T'>, were obtained by an eddy covariance system (ECS), coupling a high-frequency (34 Hz) single-point current meter and a temperature sensor. Vertical/temporal properties of near-inertial waves were obtained by a downward-looking ADCP, collocated with ECS on the same ice floe. At same time, a triangle of high-precision GPS systems tracked ice movement to represent mean drift speed, rotation and deformation about the same floe seamlessly in time. Preliminary analyses of those combined data suggested that pronounced signals of inertial motion occurred in early September of 2020 as sheer ice keels dragged underlying waters, stratified by accumulation of melt water. It then allowed occurrence of near-inertial internal waves that tend to be trapped within the interfacial boundary layer, located within top 20 m. At the conference, we will present latest and quantitative knowledges from the MOSAiC expedition.</p>

scholarly journals On simulating high-frequency variability in Antarctic sea-ice dynamics models

1998 ◽  
Vol 27 ◽  
pp. 443-448 ◽  
Author(s):  
W. D. Hibler III ◽  
Petra Heil ◽  
Victoria I. Lytle
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
High Frequency ◽  
Ice Dynamics ◽  
Antarctic Sea Ice ◽  
Sea Ice Dynamics ◽  
Ice Drift ◽  
Dynamics Models ◽  
The Antarctic ◽  
Ocean Boundary

Due to frequent and intense storm systems moving across the Antarctic sea ice, ice drift and deformation fluctuate substantially. Observations of drilling buoys show inertial power to be a substantial component of ice drift and deformation. Because the inertial period at high latitudes is close to tidal periods, this peak can be amplified due to resonance. in practice, the energy dissipation by ice interaction plays a significant role in dampening out this inertial energy. in present sea-ice dynamics models both with and without ice interaction, this inertial motion is overdamped due to the underestimation of coupling to the ocean boundary layer. To develop a more consistent treatment of ice drift under fluctuating wind fields, we consider here a vertically integrated formulation of the ice-ocean boundary-layer system that incorporates a more realistic treatment of the upper ocean. Under steady wind conditions this model reduces to the normal water-drag formulation used in most sea-ice dynamics models. Simulations using this “imbedded” model are analyzed to elucidate the role of ice interaction in the Antarctic ice-pack in modifying the high-frequency motion and inducing deformation which in turn significantly impact ice-thickness characteristics. The simulations demonstrate that in an interacting ice field in the presence of kinematic waves inertial imbedding can lead to oscillations in ice concentration of up to ~10% open water. These variations are similar in magnitude to observed deformation fluctuations in tide-free regions.

scholarly journals Airborne observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

2015 ◽  
Vol 15 (14) ◽  
pp. 8147-8163 ◽  
Author(s):  
M. Schäfer ◽  
E. Bierwirth ◽  
A. Ehrlich ◽  
E. Jäkel ◽  
M. Wendisch
Keyword(s):  
Boundary Layer ◽  
Radiative Transfer ◽  
Sea Ice ◽  
Three Dimensional ◽  
Open Water ◽  
Radiative Effects ◽  
Arctic Boundary Layer ◽  
Boundary Layer Clouds ◽  
Ice Edge ◽  
Ice Floes

Abstract. Based on airborne spectral imaging observations, three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and highly variable Arctic surfaces were identified and quantified. A method is presented to discriminate between sea ice and open water under cloudy conditions based on airborne nadir reflectivity γλ measurements in the visible spectral range. In cloudy cases the transition of γλ from open water to sea ice is not instantaneous but horizontally smoothed. In general, clouds reduce γλ above bright surfaces in the vicinity of open water, while γλ above open sea is enhanced. With the help of observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge (for a dark-ocean albedo of αwater = 0.042 and a sea-ice albedo of αice = 0.91 at 645 nm wavelength). The affected distance Δ L was found to depend on both cloud and sea ice properties. For a low-level cloud at 0–200 m altitude, as observed during the Arctic field campaign VERtical Distribution of Ice in Arctic clouds (VERDI) in 2012, an increase in the cloud optical thickness τ from 1 to 10 leads to a decrease in Δ L from 600 to 250 m. An increase in the cloud base altitude or cloud geometrical thickness results in an increase in Δ L; for τ = 1/10 Δ L = 2200 m/1250 m in case of a cloud at 500–1000 m altitude. To quantify the effect for different shapes and sizes of ice floes, radiative transfer simulations were performed with various albedo fields (infinitely long straight ice edge, circular ice floes, squares, realistic ice floe field). The simulations show that Δ L increases with increasing radius of the ice floe and reaches maximum values for ice floes with radii larger than 6 km (500–1000 m cloud altitude), which matches the results found for an infinitely long, straight ice edge. Furthermore, the influence of these 3-D radiative effects on the retrieved cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge results in uncertainties of up to 90 and 30 % in retrievals of τ and effective radius reff, respectively. With the help of Δ L, an estimate of the distance to the ice edge is given, where the retrieval uncertainties due to 3-D radiative effects are negligible.

scholarly journals The importance of capturing late melt season sea ice conditions for modeling the western Arctic ocean boundary layer

Elem Sci Anth ◽  
2019 ◽  
Vol 7 ◽  
Author(s):  
Shawn G. Gallaher
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Late Summer ◽  
Open Water ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Near Surface ◽  
Ice Conditions ◽  
Western Arctic ◽  
Ocean Boundary

To better understand the response of the western Arctic upper ocean to late summer ice-ocean interactions, a range of surface, interior, and basal sea ice conditions were simulated in a 1-D turbulent boundary layer model. In-ice and under-ice autonomous observations from the 2014 Marginal Ice Zone Experiment provided a complete characterization of the late melt-season sea ice and were used to set initial conditions, update boundary conditions, and conduct model validation studies. Results show that underestimates of open water and melt pond fraction at the sea ice surface had the largest influence on ocean-to-ice turbulent heat fluxes reducing basal melt rates by as much as 32%. This substantial reduction in latent heat loss was attributed to underestimates of open water areas and the exclusion of melt ponds by low-resolution synthetic aperture radar imagery. However, the greatest overall effect on the ice-ocean boundary layer came from mischaracterizations of basal roughness, with smooth ice scenarios resulting in 7 m of summer halocline shoaling and preservation of the near-surface temperature maximum. Rough ice conditions showed a 23% deepening of the mixed layer and erosion of heat storage above 40 m. Adjustments of conductive heat fluxes had little effect on the near-interface heat budget due to small internal thermal gradients within the late summer sea ice. Results from the 1-D boundary layer simulations highlight the most influential components of sea ice structure during late summer conditions and provide the magnitude of errors expected when ice conditions are mischaracterized.

scholarly journals Year-round observations of sea-ice drift and near-inertial internal waves in the Northwind Abyssal Plain, Arctic Ocean

Polar Science ◽  
2019 ◽  
Vol 21 ◽  
pp. 212-223 ◽  
Author(s):  
Yusuke Kawaguchi ◽  
Motoyo Itoh ◽  
Yasushi Fukamachi ◽  
Erika Moriya ◽  
Jonaotaro Onodera ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Internal Waves ◽  
Abyssal Plain ◽  
Ice Drift ◽  
Sea Ice Drift

scholarly journals Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

2016 ◽  
Vol 29 (10) ◽  
pp. 3767-3785 ◽  
Author(s):  
G. Gastineau ◽  
B. L’Hévéder ◽  
F. Codron ◽  
C. Frankignoul
Keyword(s):  
Heat Flux ◽  
Sea Ice ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Late Winter ◽  
Atmospheric Response ◽  
Overturning Circulation ◽  
The North ◽  
Eddy Heat Flux ◽  
The North Atlantic

Abstract In climate models, an intensification of the Atlantic meridional overturning circulation (AMOC) precedes a warming in the North Atlantic subpolar basin by a few years. In the IPSL-CM5A-LR model, this warming may explain the atmospheric response to the AMOC observed in winter, which resembles a negative phase of the North Atlantic Oscillation (NAO). To firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in this model, ensembles of atmosphere-only simulations are conducted, prescribing the SST and sea ice anomalies that follow an AMOC intensification. In late winter, the North Atlantic SST and sea ice anomalies drive atmospheric circulation anomalies similar to those found in the coupled model. Simulations only driven by the SST anomalies related to the AMOC show that the largest oceanic influence is due to the warm subpolar SST anomaly, which enhances the oceanic heat release and decreases the lower-tropospheric baroclinicity in the region of maximum eddy growth, resulting in a weaker meridional eddy heat flux in the atmosphere. The transient eddy feedback leads to a negative NAO-like response. An AMOC intensification is also followed by less sea ice over the Labrador Sea and more sea ice over the Nordic seas. The simulations with full boundary forcing suggest that such anomalies act to strengthen both the poleward momentum flux and the upward heat flux into the polar stratosphere and lead to a stratospheric warming, which then reinforces the negative NAO signal in late winter.

scholarly journals Characterizing sudden changes in Arctic sea ice drift and deformation on synoptic timescales

2016 ◽  
Author(s):  
Jennifer V. Lukovich ◽  
Cathleen A. Geiger ◽  
David G. Barber
Keyword(s):  
Sea Ice ◽  
Oil And Gas ◽  
Beaufort Sea ◽  
Arctic Sea Ice ◽  
Ice Drift ◽  
Shock Response ◽  
Near Shore ◽  
Sea Ice Drift ◽  
Ice Conditions ◽  
Ice Floes

Abstract. In this study, we develop a framework for the assessment of sudden changes in sea ice drift and associated deformation processes in response to atmospheric forcing and ice–coastal interactions, based on analysis of ice buoy triplet centroids and areas. Examined in particular is the spatiotemporal evolution in sea ice floes that are tracked with GPS beacons deployed in triplets in the southern Beaufort Sea at varying distances from the coastline in fall, 2009 – triplets A to D, with A (D) located closest to (furthest from) the coastline. This study illustrates the use of shock-response diagnostics to evaluate eight identified sudden changes or shock events on daily timescales. Results from this analysis show that shock events in the southern Beaufort Sea occur in at least one of two forms: (1) during a reversal in winds, or (2) sustained north/easterly winds, with response mechanisms governed by ice conditions and interactions with the coastline. Demonstrated also is the emergence of a shear-shock event (SSE) that results in reduced ice concentrations for triplets B, C, and D, one, three and five days following the SSE, respectively and loss of synchronicity in ice-atmosphere interactions. The tools developed in this study provide a unique characterization of sea ice dynamical processes in the southern Beaufort Sea, with implications for quantifying "shock-response" systems relevant for ice hazard assessments and forecasting applications required by oil and gas, marine transportation, and indigenous use of near shore Arctic areas.

scholarly journals Observations and simulations of three-dimensional radiative interactions between Arctic boundary layer clouds and ice floes

2015 ◽  
Vol 15 (2) ◽  
pp. 1421-1469 ◽  
Author(s):  
M. Schäfer ◽  
E. Bierwirth ◽  
A. Ehrlich ◽  
E. Jäkel ◽  
M. Wendisch
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Optical Thickness ◽  
Three Dimensional ◽  
Open Water ◽  
Arctic Boundary Layer ◽  
Boundary Layer Clouds ◽  
Cloud Optical Thickness ◽  
Ice Edge ◽  
Ice Floes

Abstract. Based on airborne spectral imaging observations three-dimensional (3-D) radiative effects between Arctic boundary layer clouds and ice floes have been identified and quantified. A method is presented to discriminate sea ice and open water in case of clouds from imaging radiance measurements. This separation simultaneously reveals that in case of clouds the transition of radiance between open water and sea ice is not instantaneously but horizontally smoothed. In general, clouds reduce the nadir radiance above bright surfaces in the vicinity of sea ice – open water boundaries, while the nadir radiance above dark surfaces is enhanced compared to situations with clouds located above horizontal homogeneous surfaces. With help of the observations and 3-D radiative transfer simulations, this effect was quantified to range between 0 and 2200 m distance to the sea ice edge. This affected distance Δ L was found to depend on both, cloud and sea ice properties. For a ground overlaying cloud in 0–200 m altitude, increasing the cloud optical thickness from τ = 1 to τ = 10 decreases Δ L from 600 to 250 m, while increasing cloud base altitude or cloud geometrical thickness can increase Δ L; Δ L(τ = 1/10) = 2200 m/1250 m for 500–1000 m cloud altitude. To quantify the effect for different shapes and sizes of the ice floes, various albedo fields (infinite straight ice edge, circles, squares, realistic ice floe field) were modelled. Simulations show that Δ L increases by the radius of the ice floe and for sizes larger than 6 km (500–1000 m cloud altitude) asymptotically reaches maximum values, which corresponds to an infinite straight ice edge. Furthermore, the impact of these 3-D-radiative effects on retrieval of cloud optical properties was investigated. The enhanced brightness of a dark pixel next to an ice edge results in uncertainties of up to 90 and 30% in retrievals of cloud optical thickness and effective radius reff, respectively. With help of Δ L quantified here, an estimate of the distance to the ice edge for which the retrieval errors are negligible is given.

Poleward eddy heat flux anomalies associated with recent Arctic sea ice loss

2017 ◽  
Vol 44 (1) ◽  
pp. 446-454 ◽  
Author(s):  
Kazuhira Hoshi ◽  
Jinro Ukita ◽  
Meiji Honda ◽  
Katsushi Iwamoto ◽  
Tetsu Nakamura ◽  
...  
Keyword(s):  
Heat Flux ◽  
Sea Ice ◽  
Arctic Sea Ice ◽  
Eddy Heat Flux ◽  
Arctic Sea ◽  
Arctic Sea Ice Loss

scholarly journals Sea ice drift and arch evolution in the Robeson Channel using the daily coverage of Sentinel-1 SAR data for the 2016–2017 freezing season

2020 ◽  
Vol 14 (11) ◽  
pp. 3611-3627
Author(s):  
Mohammed E. Shokr ◽  
Zihan Wang ◽  
Tingting Liu
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Linear Trend ◽  
Ice Cover ◽  
The Arctic ◽  
Sar Images ◽  
Ice Drift ◽  
Sea Ice Drift ◽  
Ice Floes

Abstract. The Robeson Channel is a narrow sea water passage between Greenland and Ellesmere Island in the Arctic. It is a pathway of sea ice from the central Arctic and out to Baffin Bay. In this study, we used a set of daily synthetic aperture radar (SAR) images from the Sentinel-1A/1B satellites, acquired between September 2016 and April 2017, to study the kinematics of individual ice floes as they approach and then drift through the Robeson Channel. The tracking of 39 selected ice floes was visually performed in the image sequence, and their speed was calculated and linked to the reanalysis 10 m wind from ERA5. The results show that the drift of ice floes is very slow in the compact ice regime upstream of the Robeson Channel, unless the ice floe is surrounded by water or thin ice. In this case, the wind has more influence on the drift. On the other hand, the ice floe drift is found to be about 4–5 times faster in the open-drift regime within the Robeson Channel and is clearly influenced by wind. A linear trend is found between the change in wind and the change in ice drift speed components, along the length of the channel. Case studies are presented to reveal the role of wind in ice floe drift. This paper also addresses the development of the ice arch at the entry of the Robeson Channel, which started development on 24 January and matured on 1 February 2017. Details of the development, obtained using the sequential SAR images, are presented. It is found that the arch's shape continued to adjust by rupturing ice pieces at the locations of cracks under the influence of the southward wind (and hence the contour kept displacing northward). The findings of this study highlight the advantage of using the high-resolution daily SAR coverage in monitoring aspects of sea ice cover in narrow water passages where the ice cover is highly dynamic. The information will be particularly interesting for the possible applications of SAR constellation systems.

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