Light Ice Research Articles

THE GEOMETRY AND ORIENTATION OF THE WATER MOLECULE IN ICE Ih

The results of a low-temperature (15K) single crystal neutron diffraction study on light and heavy ice Ih are presented. The reduced thermal motions allow the analysis of the nature and magnitude of the molecular disorder in some detail. The disorder deformation densities show significant differences in H2O and D2O ice Ih indicating that heavy ice Ih is slightly less disordered (more structured) than light ice Ih. The absolute magnitude of the disorder can be deduced from the combination of spectroscopic and crystallographic data, and consistently D2O ice Ih is found to show the emaller disorder displacements. The introduction of molecular disorder leads to OH(D) distances in good agreement with recent quantum chemical calculations, while the theoretical estimate for the intermolecular hydrogen-bonded distances is clearly higher than the observed values indicating that the cooperativity of the hydrogen bonding has not been fully accounted for.

Minimum Flashover Voltage of Iced Insulators

Experimental studies were performed in a 4.8×2.8×3.5 m3 cold room with a HV transformer of 124 kVA, 120 kV. Atmospheric ice was accreted on a vertical string of three types of insulators: a classic glass insulator and two long-rod synthetic insulators. The results obtained show that flashover occurs at the lowest voltage with hard rime formed at -12°C with a density of 0.87. With hard rime it is found that the minimum flashover voltage of the glass insulator used is about 40% of that of a wet insulator. The minimum flashover voltage measured without applied voltage during the icing period is higher than that obtained with voltage applied during icing. Except for very light icing conditions, the length of icicles is a less accurate parameter for the measurement of the severity of the icing than the thickness of ice accreted on a monitoring conductor. For clean iced insulators, it is found that the minmum flashover voltage decreases with increasing thickness of ice up to 2 cm. In addition, the results obtained show that the minimum flashover voltage is linearly proportional to the arc path on iced insulators, i.e. the sum of the spacings and the leakage distance of one clean insulator. It is shown that the effect of the thickness of ice on precontaminated iced insulators, decreases with increasing degree of the contamination.

Arctic marine oil spill research

Canada, with its immense arctic and subarctic regions, wants to develop the promising hydro-carbon potential of the Beaufort Sea, the high arctic islands, the eastern arctic and Labrador. Of necessity, Canada has gradually become a world leader in arctic marine oil spill research. Some of this research has been done by the Canadian federal government through AMOP, the Arctic Marine Oilspill Project. There has been joint oil industry/government research, such as the Beaufort Sea Project and the Baffin Island Oil Spill Project. In oil company initiatives, Dome Petroleum has been a leader in the Beaufort Sea region. Finally, a cooperative oil industry organization, the Arctic Petroleum Operators' Association and its research group, the Canadian Offshore Oil Spill Research Association, have made many important studies. Initial efforts aimed to strengthen existing containment and recovery equipment to operate in light ice conditions. When the limits of this technology were rapidly reached, research turned to developing burning techniques, including fireproof booms, in situ burning against ice edges and in spring melt pools, air deployable igniters and portable burners and incinerators. New dispersant technology was developed for aerial application, for cold water dispersion and for solidification. The effects of dispersed oil in the arctic nearshore and onshore environment were assessed. More recently, subsea containment has become an important area of study. Future research will include methods of mechanical recovery of oil in ice, oil/water emulsions in and under ice, and the mechanism of oil migration upward through pack ice.

Cyclone Climatology of the Bering Sea and Its Relation to Sea Ice Extent

A monthly storm-track climatology is derived from monthly maps of cyclone tracks for the winter season, October through March, averaged over 23 years, 1957/58–1979/80, for a 2° latitude×4° longitude grid bounded by 51°N, 65°N, 157°W and 171°E. There is a decrease in the number of cyclones with latitude in all months and division into two storm tracks, one propagating north-northeast along the Siberian peninsula and one entering the southern Bering Sea on a northeasterly course and either curving northward into the central Bering Sea or continuing parallel to the Aleutian Island chain. Monthly average ice extents are established for February and March 1958–80 along a line from Norton Sound southwest toward the ice edge, perpendicular to the average maximum extent. Comparison of composite cyclone charts summed over the winter season and over the five heaviest and five lightest ice years shows a shift in cyclone centers toward the west in light ice years. The correlation between maximum seasonal ice extent and the difference between the number of cyclone centers in the eastern minus the western part of the basin over each winter season is 0.71. The relation of sea ice extent and the location of cyclone tracks is consistent with previous observations that advance of the ice edge in the Bering Sea is dominated by wind-driven advection and that southerly winds associated with cyclone tracks to the west inhibit this advance. These results indicate that the interannual variability in seasonal sea-ice extent in the Bering Sea is controlled by an externally determined variation in storm-track position related to large-scale differences in the general circulation. A skewed distribution of ice extents toward heavy ice years, however, suggests the possibility of an oceanographic constraint on the magnitude of extreme seasonal ice extents, such as the inability of melting ice to cool the mixed layer beyond the continental shelf to the freezing point or the increased influence of the northwestward flowing, continental slope current.

Monthly and seasonal variability in the ocean‐ice‐atmosphere systems of the North Pacific and the North Atlantic

Four regional indices of sea ice variability and thirty years of monthly sea surface temperature (SST) and sea level pressure (SLP) data are used to evaluate the large‐scale interactions within the ocean‐ice‐atmosphere systems of the North Pacific and the North Atlantic. A direct association between positive (negative) SST anomalies and light (heavy) ice in the Bering Sea is indicated. The SST/ice coupling in the northern Alaskan waters is also statistically significant. The SST anomalies in both the North Pacific and the North Atlantic appear as persistent responses to atmospheric forcing. The SLP distributions over both oceans correlate significantly with the arctic SLP distribution, although the midlatitude atmospheric circulation shows no systematic tendency to lead or lag the arctic circulation. Sea ice fluctuations correlate most highly with the atmospheric forcing over antecedent periods of approximately 9 months in the northern Alaskan waters, 3–4 months in the Bering Sea, and 5–7 months in the East Greenland Sea. The strength of the 9‐month mean onshore air flow component describes over 70% of the northern Alaskan ice variance.

Stress amplification under a moving load on floating ice

The plane‐wave solution found in earlier work for the response of a viscoelastic floating plate to a moving line load is evaluated for a variety of conditions that might occur for floating ice sheets. The equivalent wave loading stress produced in a thin ice sheet by a line load moving at the critical speed is found to exceed the applied static loading stress by a substantial factor. As the ice thickness or the modulus increases, or the water depth decreases, the maximum loading factor decreases. The response of a floating ice sheet to a moving vehicle is discussed in the light of this behavior. The results suggest that ice less than 0.25 m thick might be efficiently broken by several relatively light ice breakers, such as air cushion vehicles, operating in a line abreast at the critical speed.

Lidar depolarization studies of the atmosphere at the South Pole

Some examples of lidar backscatter and depolarization profiles obtained at the South Pole during the austral summer period 1976-77 are presented. The examples illustrate the variety of data obtainable from various meteorological conditions as well as how this kind of lidar can help determine cloud layer structures in the polar atmosphere. Clear sky ice crystal precipitation and light ice precipitation under overcast sky conditions produced volume backscatter coefficients in the 2-4 x 10(-3)-km(-1) range and depolarization values up to 0.46, while mixed phase and supercooled water drop layers were also observed with maximum backscatter coefficients ranging from 5 x 10(-2) to 2.4 x 10(-1) km(-1) and depolarization values from a few to ~20%. Some of these layers may have contained aligned plates which resulted in enhanced backscatter values and lower depolarization values, therefore, the identification is sometimes ambiguous.

Some characteristics of sea ice in the antarctic in comparison with the arctic

Abstract Fast ice is generally less developed in the Antarctic than in the Arctic because of the steeper shores and lesser dissection of the Antarctic coast. Polynyas in the Antarctic are shown by space imagery to occur mainly off the west shore of ice shelves or land cusps extending far into the sea. Satellite photography also shows that ice conditions around Antarctica are associated with atmospheric circulation patterns, with light ice prevailing during a zonal pattern and heavy ice during a meridional pattern. In some regions of the Antarctic, fluctuations in the amount of ice are found to be cyclic, with the same period as in Arctic seas.

Positron Lifetimes in Pure and Doped Ice and in Water

Positron lifetime spectra were measured in mono- and polycrystalline light ice, polycrystalline heavy ice, doped light ice, as well as in light and heavy water. All spectra were resolved into three components. At temperatures between −196° and −100°C the lifetimes and relative intensities are virtually constant, being 0.12 nsec and 20%, 0.44 nsec and 28%, 0.68 nsec and 52%, and attributed to annihilation of para-Ps, free positrons, and ortho-Ps, respectively. Above −100°C the longest lifetime increases with temperature to 1.1 nsec at 0°C. Its relative intensity is unchanged, while the parameters for the other components show a complex behavior. The spectra for mono- and polycrystalline light ice and for polycrystalline heavy ice are identical. For water long lifetime components attributed to ortho-Ps are 1.86 nsec, 27% for H2O and 2.01 nsec, 22% for D2O. Theoretical explanations are suggested. Fast frozen solutions of HF with concentrations larger than approximately 10−5 mole fraction have a lifetime component at −160°C of 1.23 nsec, 52% attributed to trapping of ortho-Ps in amorphous regions. Very good agreement is found between the experiments and a trapping model. Irreversible changes of the spectra are found by heating above approximately −120°C. Measurements on a number of fast frozen aqueous solutions of acids, bases, and salts are reported, none of them showing as strong influence on the ortho-Ps lifetime as HF.

Pulsed-Neutron Diffusion Parameters in Mixtures of Heavy and Light Water and Ice

The diffusion parameters for mixtures of 0, 20, 50, 80, and 100% D2O in H2O have been measured by the pulsed-neutron method at temperatures near the freezing point and in ice at −20°C. A 250-keV Co...

Phonon Spectrum and Thermal Neutron Scattering in Light Water Ice

The phonon spectrum of light water ice at 0°C is computed by the root sampling method for a sampling of 1,050 points in an irreducible sampling region of the first Brillouin zone. The scattering law for thermal neutron scattering in hexagonal ice is also calculated and found to agree well with reported experimental values.

Mechanische D�mpfung von D2O-Einkristallen

The mechanical resistance of D₂O crystals, approxi-mately 12 cm long and 1.5 cm in diameter, was measured at frequeneies from 0.2 to 4 kHz and at temperatures from -90 to + 2 deg C. The results showed that the resistance of D₂O crystals has the same dependence on temperature and frequency, oscillation type, and crystallographic orientation as light ice. The activation energy, determined from the temperature dependence of the resistance maxima, has the same value as that of H₂O crystals. The frequency displacement was calculated. (J. S.R.)

Reviews and abstracts

The recent appearance of the 1939 issue of this unique publication marks the return after an absence of several years of the annual report of Arctic ice conditions. Five plates in color showing the mean monthly ice limits for April, May, June, July, and August follow 16 pages of text describing conditions in greater or lesser detail in different parts of the Arctic.In the Greenland Sea the ice was considerably below the normal except in the estuaries of the fjords on the northeast coast. There the ice melted very slowly owing to the unusual combination of very heavy ice encrusted snow on the sea ice, and the absence of any gales during June and July which normally break up the ice at these points. The coasts of Iceland were free of ice throughout the year which is the sixth year in the 1930's with such unusually light ice conditions off Iceland. The light ice conditions in the Greenland Sea were associated with unusually severe ice conditions off Newfoundland and Labrador, another instance of a previously noted inverse relationship between ice in the Greenland Sea and ice off Newfoundland.