Aerial observations of the evolution of ice surface conditions during summer
TL;DR: In the summer of 1998, a program of aerial photography was carried out at the main site of the Surface Heat Budget of the Arctic Ocean (SHEBA) program at altitudes ranging from 1220 to 1830 m as mentioned in this paper.
Abstract: [1] During spring and summer, the Arctic pack ice cover undergoes a dramatic change in surface conditions, evolving from a uniform, reflective surface to a heterogeneous mixture of bare ice, melt ponds, and leads. This transformation is accompanied by a significant decrease in areally averaged, integrated albedo. The key factors contributing to this reduction in albedo are the melting of the snow cover, the formation and growth of the melt ponds, and the increase in the open water fraction. To document these changes and enable quantification of the evolution of the ponds throughout the melt season, a program of aerial photography was carried out at the main site of the Surface Heat Budget of the Arctic Ocean (SHEBA) program. A modified square pattern, 50 km on a side, surrounding the SHEBA site was flown at altitudes ranging from 1220 to 1830 m. Twelve of these aerial survey photography flights were completed between 20 May and 4 October 1998. The flights took place at approximately weekly intervals at the height of the melt season, with occasional gaps as long as 3 weeks during August and September due to persistent low clouds and fog. In addition, flights on 17 May and 25 July were flown in a closely spaced pattern designed to provide complete photo coverage of a 10-km square centered on the SHEBA main site. Images from all flights were scanned at high resolution and archived on CD-ROMs. Using personal computer image processing software, we have measured ice concentration, melt pond coverage, statistics on size and shape of melt ponds, lead fraction, and lead perimeter for the summer melt season. The ponds began forming in early June, and by the height of the melt season in early August the pond fraction exceeded 0.20. The temporal evolution of pond fraction displayed a rapid increase in mid-June, followed by a sharp decline 1 week later. After the decline, the pond fraction gradually increased until mid-August when the ponds began to freeze. By mid-September the surface of virtually all of the ponds had frozen. The open water fraction varied between 0.02 and 0.05 from May through the end of July. In early August the open water fraction jumped to 0.20 in just a few days owing to ice divergence. Melt ponds were ubiquitous during summer, with number densities increasing from 1000 to 5000 ponds per square kilometer between June and August.
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TL;DR: The Surface Heat Budget of the Arctic Ocean (SHEBA) project as discussed by the authors collected ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges.
Abstract: A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goal...
575 citations
TL;DR: In this article, the spectral and wavelength-integrated albedo on multi-year sea ice was measured every 2.5 m along a 200m survey line from April through October.
Abstract: [1] As part of ice albedo feedback studies during the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, we measured spectral and wavelength-integrated albedo on multiyear sea ice. Measurements were made every 2.5 m along a 200-m survey line from April through October. Initially, this line was completely snow covered, but as the melt season progressed, it became a mixture of bare ice and melt ponds. Observed changes in albedo were a combination of a gradual evolution due to seasonal transitions and abrupt shifts resulting from synoptic weather events. There were five distinct phases in the evolution of albedo: dry snow, melting snow, pond formation, pond evolution, and fall freeze-up. In April the surface albedo was high (0.8–0.9) and spatially uniform. By the end of July the average albedo along the line was 0.4, and there was significant spatial variability, with values ranging from 0.1 for deep, dark ponds to 0.65 for bare, white ice. There was good agreement between surface-based albedos and measurements made from the University of Washington's Convair-580 research aircraft. A comparison between net solar irradiance computed using observed albedos and a simplified model of seasonal evolution shows good agreement as long as the timing of the transitions is accurately determined.
444 citations
Journal Article•
TL;DR: In this paper, the authors measured spectral and wavelength-integrated albedo on multi-year sea ice from a 200m survey line from April through October and observed changes in the evolution of albedos.
Abstract: [1] As part of ice albedo feedback studies during the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, we measured spectral and wavelength-integrated albedo on multiyear sea ice. Measurements were made every 2.5 m along a 200-m survey line from April through October. Initially, this line was completely snow covered, but as the melt season progressed, it became a mixture of bare ice and melt ponds. Observed changes in albedo were a combination of a gradual evolution due to seasonal transitions and abrupt shifts resulting from synoptic weather events. There were five distinct phases in the evolution of albedo: dry snow, melting snow, pond formation, pond evolution, and fall freeze-up. In April the surface albedo was high (0.8-0.9) and spatially uniform. By the end of July the average albedo along the line was 0.4, and there was significant spatial variability, with values ranging from 0.1 for deep, dark ponds to 0.65 for bare, white ice. There was good agreement between surface-based albedos and measurements made from the University of Washington's Convair-580 research aircraft. A comparison between net solar irradiance computed using observed albedos and a simplified model of seasonal evolution shows good agreement as long as the timing of the transitions is accurately determined.
422 citations
TL;DR: In this paper, the authors examined the impact of seasonal ice cover on sea ice albedo and found that the shift from a multi-year to seasonal cover has significant implications for the heat and mass budget of the ice and for primary productivity in the upper ocean.
Abstract: [1] There is an ongoing shift in the Arctic sea ice cover from multiyear ice to seasonal ice. Here we examine the impact of this shift on sea ice albedo. Our analysis of observations from four years of field experiments indicates that seasonal ice undergoes an albedo evolution with seven phases; cold snow, melting snow, pond formation, pond drainage, pond evolution, open water, and freezeup. Once surface ice melt begins, seasonal ice albedos are consistently less than albedos for multiyear ice resulting in more solar heat absorbed in the ice and transmitted to the ocean. The shift from a multiyear to seasonal ice cover has significant implications for the heat and mass budget of the ice and for primary productivity in the upper ocean. There will be enhanced melting of the ice cover and an increase in the amount of sunlight available in the upper ocean.
323 citations
Cites background from "Aerial observations of the evolutio..."
...In contrast, multiyear ice, with its undulating topography, typically has peak pond fractions of only 0.3–0.4 [Fetterer and Untersteiner, 1998; Perovich et al., 2002a; Tschudi et al., 1997] because meltwater is collected into deeper ponds with less area....
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...Integrated over an entire summer melt cycle these omissions will have modest impact [Perovich et al., 2002a]....
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TL;DR: The Community Climate System Model, version 4 has revisions across all components and the most notable improvements are the incorporation of a new shortwave radiative transfer scheme and the capabilities that this enables.
Abstract: The Community Climate System Model, version 4 has revisions across all components. For sea ice, the most notable improvements are the incorporation of a new shortwave radiative transfer scheme and the capabilities that this enables. This scheme uses inherent optical properties to define scattering and absorption characteristics of snow, ice, and included shortwave absorbers and explicitly allows for melt ponds and aerosols. The deposition and cycling of aerosols in sea ice is now included, and a new parameterization derives ponded water from the surface meltwater flux. Taken together, this provides a more sophisticated, accurate, and complete treatment of sea ice radiative transfer. In preindustrial CO2 simulations, the radiative impact of ponds and aerosols on Arctic sea ice is 1.1 W m−2 annually, with aerosols accounting for up to 8 W m−2 of enhanced June shortwave absorption in the Barents and Kara Seas and with ponds accounting for over 10 W m−2 in shelf regions in July. In double CO2 (2XCO2) ...
320 citations
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11,456 citations
TL;DR: In this article, the authors investigated the response of a climate model to a gradual increase or decrease of atmospheric carbon dioxide in a general circulation model of the coupled atmosphere-ocean-land surface system with global geography and seasonal variation of insulation.
Abstract: This study investigates the response of a climate model to a gradual increase or decrease of atmospheric carbon dioxide The model is a general circulation model of the coupled atmosphere-ocean-land surface system with global geography and seasonal variation of insulation To offset the bias of the coupled model toward settling into an unrealistic state, the fluxes of heat and water at the ocean-atmosphere interface are adjusted by amounts that vary with season and geography but do not change from one year to the next Starting from a quasi-equilibrium climate, three numerical time integrations of the coupled model are performed with gradually increasing, constant, and gradually decreasing concentration of atmospheric carbon dioxide It is noted that the simulated response of sea surface temperature is very slow over the northern North Atlantic and the Circumpolar Ocean of the Southern Hemisphere where vertical mixing of water penetrates very deeply However, in most of the Northern Hemisphere an
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TL;DR: In this article, the authors measured light transmission and reflection on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher's Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.).
Abstract: Measurements of light transmission and reflection were carried out on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher’s Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.). Spectral albedos (400-1 000 nm) and extinction coefficients (400-800 nm) were determined for melt ponds, snow, and various types of bare ice. Albedos were largest in the 400-600 nm range, decreasing toward longer wavelengths at a rate which appeared to be related to the liquid-water content of the near-surface layers. Extinction coefficients remained nearly constant between 400 and 550 nm, but increased rapidly above 600 nm. At 500 nm, albedos ranged from 0.25 over mature melt ponds to 0.93 over dense dry snow, while the corresponding extinction coefficients ranged from 0.6 to 16 m-1. Intensity profiles taken in the upper 50 cm of the ice indicated that the extinction coefficient at a particular wavelength was nearly constant with depth below 15 cm, although the bulk extinction coefficient decreased with depth because of the strong attenuation in the red. Near the surface it was found that multi-year ice absorbed slightly more energy than did first-year blue ice, but at depths below 10 cm the flux divergence in the first-year ice was three to four times larger than that in the multi-year ice. A simple procedure is described for estimating light transmission and absorption within the ice under clear or cloudy skies from total flux measurements at the surface. Methods by which satellite data could be used to estimate regional albedos, melt-pond fraction, and lead area are also presented.
576 citations
TL;DR: The Surface Heat Budget of the Arctic Ocean (SHEBA) project as discussed by the authors collected ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges.
Abstract: A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goal...
575 citations