Air Ice Research Articles

Air–Ice–Ocean Momentum Exchange. Part 1:Energy Transfer between Waves and Ice Floes

Abstract The energy exchange between ocean surface waves and ice floes in the marginal ice zone (MIZ) involves the scattering and attenuation of wave energy and the excitation of oscillation modes of the ice floes, as open ocean waves propagate into the MIZ. Heave, pitch, and roll modes of oscillation are linked to estimation of wave scattering and attenuation. A model is presented for wave attenuation and compared to measurements from the Marginal Ice Zone Experiments in the Greenland Sea, as reported by Wadhams et al.

The Antarctic Zone Flux Experiment

In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations s...

Late glacial air temperature, oceanographic and ice sheet interactions in the southern Barents Sea region

Abstract Stratigraphic records from three areas (the Andøya area, the continental slope and the continental shelf of the southern Barents Sea) are used to evaluate the history of the late glacial Barents Sea Ice Sheet and the northern Fennoscandian Ice Sheet. Two late glacial maxima are indicated: one before 22 ka BP (LGM I) and the younger after 19 ka BP (LGM II). A major deglaciation phase was initiated during a warm spell between 16 and 15 ka BP . During a drawdown of marine based ice sheets about 14.5 ka BP large parts of the southern Barents Sea Ice Sheet decayed. This deglaciation was retarded between 13.7 and 13 ka BP . Most of the eastern and northern Barents Sea was deglaciated during the Bølling-Allerød interstadial complex. During the LGM II there was an ice stream in the Bear Island Trough with an estimated velocity at the front of about 2.5 km/year. An average accumulation rate of 0.3–0.4 m/year is estimated for the drainage area of the Bear Island Trough Ice Stream. A close interrelation exists between summer air temperatures and the waxing and waning phases of the northern Fennoscandian and southern Barents Sea ice sheets. It is suggested that most of the ice sheet decay was due to climatic warming, which caused thinning of the ice sheets, making them susceptible to decoupling from the sea bed and increased calving. The subsequent halts/readvances were due to climatic deteriorations caused by huge inputs of icebergs to the Norwegian Sea which cooled the surface water and in turn promoted sea ice preservation through the summer season and thereby increased the albedo.

Recent changes in the North American Arctic boundary layer in winter

Analysis of significant level radiosonde data from a network of Arctic stations reveals a systematic reduction in midwinter surface‐based inversion depths over the past few decades, accompanied by a rise in surface temperature. Similar trends are observed over a wide sector, from 62°W to 162°W and from 70°N to 83°N. Possible causes for these changes include increases in warm air advection, cloud cover, ice crystals, aerosols, and greenhouse gases, but the specific reasons are difficult to identify, due to strong interactions between many potentially important factors. Nevertheless, the changes are significant for studies of Arctic haze, since the midwinter stable boundary layer has been decreasing in depth over time.

Absence of evidence for greenhouse warming over the Arctic Ocean in the past 40 years

ATMOSPHERIC general circulation models predict enhanced greenhouse warming at high latitudes1 owing to positive feedbacks between air temperature, ice extent and surface albedo2–4. Previous analyses of Arctic temperature trends have been restricted to land-based measurements on the periphery of the Arctic Ocean5,6. Here we present temperatures measured in the lower troposphere over the Arctic Ocean during the period 1950–90. We have analysed more than 27,000 temperature profiles, measured by radiosonde at Russian drifting ice stations and by dropsonde from US ‘Ptarmigan’ weather reconnaissance aircraft, for trends as a function of season and altitude. Most of the trends are not statistically significant. In particular, we do not observe the large surface warming trends predicted by models; indeed, we detect significant surface cooling trends over the western Arctic Ocean during winter and autumn. This discrepancy suggests that present climate models do not adequately incorporate the physical processes that affect the polar regions.

Great Lakes Winter-Weather 700-hPa PNA Teleconnections

Abstract A positive 700-hPa Pacific-North America (PNA) circulation index in December 1989 was replaced by a negative PNA index in January and February 1990. This circulation pattern reversal was associated with an anomaly reversal in air temperatures over the eastern half of the United States and anomaly reversals in the air temperature, snowfall, and ice cover of the Great Lakes. Evidence of PNA teleconnections with these Great Lakes climatic variables for a 20-winter base period is presented through correlations of anomalies in the monthly 700-hPa PNA index and PNA coordinates with anomalies in Great Lakes average monthly air temperature, snowfall, and ice cover.

Feedback Mechanism Among Decadal Oscillations in Northern Hemisphere Atmospheric Circulation, Sea Ice, and Ocean Circulation

Decadal oscillations of the ice cover in the Barents Sea are examined for the period since 1950. They are highly correlated with atmospheric circulation when that circulation has an anomalous low pressure over the Barents Sea and Eurasian Basin, while the ice cover is weakly correlated with local air temperature. A feedback mechanism between Barents Sea ice and the atmospheric circulation is suggested; increased cyclonic wind-stress curl reduces cold Arctic flow to the Barents Sea and reduces the sea ice. The reduced ice cover encourages heat flux from the Barents Sea to the atmosphere, tending to reinforce the low pressure. This positive feedback amplifies the oscillations of the air–ice–ocean system driven by external forcing with relatively weak decadal variability. A two-level ocean model, which is driven by prescribed buoyancy flux and wind stresses, confirms that Arctic outflow to the Barents Sea decreases during a cyclonic wind stress.

Feedback Mechanism Among Decadal Oscillations in Northern Hemisphere Atmospheric Circulation, Sea Ice, and Ocean Circulation

Decadal oscillations of the ice cover in the Barents Sea are examined for the period since 1950. They are highly correlated with atmospheric circulation when that circulation has an anomalous low pressure over the Barents Sea and Eurasian Basin, while the ice cover is weakly correlated with local air temperature. A feedback mechanism between Barents Sea ice and the atmospheric circulation is suggested; increased cyclonic wind-stress curl reduces cold Arctic flow to the Barents Sea and reduces the sea ice. The reduced ice cover encourages heat flux from the Barents Sea to the atmosphere, tending to reinforce the low pressure. This positive feedback amplifies the oscillations of the air–ice–ocean system driven by external forcing with relatively weak decadal variability. A two-level ocean model, which is driven by prescribed buoyancy flux and wind stresses, confirms that Arctic outflow to the Barents Sea decreases during a cyclonic wind stress.

Thermal budget of river ice covers during breakup

The magnitude and relative importance of atmosheric (air–ice) and hydrothermal (water–ice) heat fluxes to intact and fragmented river ice covers are studied for the case of a thermal breakup. Based on field measurements obtained from the Liard River, the atmospheric sources are shown to be dominant during the period of intact ice cover. Radiation was the primary heat source, but its effect was reduced by a granulation of the decaying columnar ice which increased the cover albedo to that comparable for melting snow. The hydrothermal heat input, even with frazil ice entrained within the flow, was comparable to that from atmospheric sources under low melt conditions. The hydrothermal heat flux dramatically increased with the arrival of the breakup front because of a rapid rise in water temperature and an increase in subsurface ice roughness. Higher surface roughness and lower albedo of the fragmented ice also increased the atmospheric heat fluxes, but these were small relative to the hydrothermal heat input near the leading edge of open water. Key words: floating ice, ice breakup, ice jams, ice melt.

Causes of interannual variability in the sea ice cover of the Eastern Bering Sea

It has been shown that large-scale weather patterns in both the tropical South Pacific (El Nino-Southern Oscillation, or ENSO, events) and the North Pacific (Pacific-North American, or PNA, patterns) have strong teleconnection effects on the air, ice, and ocean environments of the Bering Sea. This signal apparently comes via the atmosphere and not the ocean. The connection between variability of the Bering Sea and the ENSO and PNA appears to be the winter position of the Aleutian Low. Interannual variability in air temperatures, ice cover, and surface winds in the Bering Sea generally are in phase with each other, whereas sea-surface temperatures (SST) tend to lag these variables by 1–3 months. These Bering Sea time-series are significantly correlated with the Southern Oscillation Index (SOI) time-series (an indicator of ENSO events) when the Bering sea data are lagged behind the SOI for up to 18 months. The correlations suggest that warming in the Bering Sea follows negative anomalies in the SOI (i.e., El Nino events). Cooling in the Bering Sea tends to follow positive anomalies (i.e., precursors of El Ninos) in the SOI. Maximal correlations for the PNA also lag the SOI by a mouth or two.

On the efficiency with which aerosol particles of radius larger than 0.1 μm are collected by simple ice crystal plates

A theoretical model is presented which allows computing the efficiency with which aerosol particles of radius 0.1≤r≤10 μm are collected by simple ice crystal plates of radius 50≤a c ≤640 μm in air of various relative humidities, temperatures and pressures. Particle capture due to thermophoresis, diffusiophoresis and inertial impaction are considered. It is shown that the capture efficiency of an ice crystal in considerably affected by phoretic effects in the range 0.1≤r≤1 μm. For aerosol particles ofr>1 μm the efficiency is strongly controlled by the flow field around the crystal and the density of the aerosol material. Trajectory analysis also predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretica results are found to agree satisfactorily with the laboratory studies presently available. Comparison shows that for the same pressure, temperature and relative humidity of the ambient air ice crystal plates are better aerosol particle scavengers than water drops.

VLF mode analysis using a ceramic dielectric model of the Earth-ionosphere waveguide

The mode content of very-low-frequency (VLF) energy propagating away from a horizontally polarized source over long ice-covered paths is studied by means of a laboratory model of the earth-ionosphere waveguide that incorporates one lossy wall. A reflecting upper boundary simulates the nighttime ionosphere; powdered ceramic materials are used at 4 GHz to represent the 15 kHz properties of air and Antarctic ice. The model is a flexible experimental tool potentially applicable to a number of propagation problems. In terms of the immediate study, namely, VLF propagation on the Antarctic continent, it is demonstrated that the three lowest TE modes are sufficient to represent the total far field under the assumed conditions. The laboratory results agree well with theoretical predictions; their relationship to ray concepts is pointed out.

On the Relation between Air Temperature and Ice Formation in the Baltic

On the Relation between Air Temperature and Ice Formation in the Baltic

On the Relation Between Air Temperature and Ice Formation in the Baltic

Ice formation in the Baltic is mainly dependent upon the meteorological elements. The problem of ice forecasting is in fact a problem of translating the weather prognosis into an ice forecast by using the relations between weather and ice. At the Swedish Meteorological and ttydrological Tnstitute in Stockholm much interest is devoted to the problem of ice forecasting, and a special section collaborating with the Central Office of the Government Icebreaking Service has been organized there. Being in charge of that section the author has been commissioned to study the relations between weather and ice. The necessary condition for ice formation is an upward net heat transport from the sea surface when the surface water temperature is at the freezing-point. This heat transport may be caused by radiation, precipitation, evaporation and conduction. But the formation of ice may at the same time be prevented by wind, by waves and currents in the sea and by the upwelling of deep water. Ice is formed when the ice producing elements dominate. On the other hand, even when these ice-producing elements are active ice may not be formed if they are suppressed by elements preventing ice formation. If we want to study this {struggle between the ice-producing and ice-preventing elements, we must be able to decide whether the ice-producing elements are active although ice is not formed. Tn this paper such a criterion will be discussed concerning that part of the heat transport which is caused by conduction. The salinity in the Baltic is low, and the freezing point is approximately o° C Furthermore, the Baltic is an almost closed sea system and its water temperature is mainly a function of the air which has been in contact with the sea surface. Therefore, instead of studying the sea temperature itself} we may examine the past air temperature. Investigations of this kind have already been made by Ostman (I950), Nusser (I950) and Palosuo (I95I). ostman adds the air temperatures only when they are below o° C, beginning with the first frost in the autumn or early winter. The result is a ¢frost-sum, which he then correlates with the ice formation in the adjacent sea. In the harbours of the northern part of the Gulf of Bothnia the ice in 62 °X0 of the cases was formed within a week before or after the occurrence of the frost-sum normally observed at ice formation. In the harbours of the southern part of the Gulf the corresponding figure is 22 °X0 and further south in the Baltic 28 °X0. For the passages along the coasts of the respective seas the figures are 26, I5 and 20 °X0 and in the open seas generally about I5 °X0. Ostman