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Ackley, S. F.

Publications and source records attributed to Ackley, S. F..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Sea ice ridging in the eastern Weddell Sea

Measurements of sea ice ridge heights and spatial frequency in the eastern Weddell Sea using a shift-based acoustical sounder are reported. A total of 933 ridges were measured along a track length of 415 km using a minimum ridge sail height of 0.75 m. The ridge frequency varied from 0.4 to 10.5 ridges per km. The mean height of the ridges was found to be about 1.1 m regardless of the ridge frequency. These results are compared to other ridging statistics from the Ross Sea and found to be similar. Comparison with Arctic data indicates that the height and frequency of the ridges are considerably less in the Weddell Sea than in the Arctic. Whereas in the Arctic, the mean ridge height tends to increase with the ridge frequency, this was not found to be the case in the Weddell Sea, where the mean ridge height remained constant irrespective of the ridge frequency. Estimates of the contribution of deformed ice to the total ice thickness are generally low except for a single 53-km section where the ridge frequency increased by an order of magnitude.

Lytle, V. I.↗
NASA NTRS1989

Passive microwave in situ observations of winter Weddell Sea ice

Results are presented on the microwave radiative characteristics of Antarctic sea ice measured during the 1986 Winter Weddell Sea Project with a set of portable radiometers. Radiometer measurements at 6, 10, 18, 37, and 90 GHz in vertical and horizontal polarizations were supplemented by near-simultaneous measurements of the ice physical characteristics (including ice thickness, salinity, temperature, snow cover, and density) made during two cruises, lasting 3 months each. Measurements were obtained on various types of sea ice over a large portion of the Weddell-Sea ice cover, including four transects across the entire ice pack. Data analysis shows a large variability in the multispectral microwave emissivities of different ice types, especially at 90 GHz, demonstrating a strong potential of the use of the 90-GHz channel, in combination with lower-frequency channels, for detailed characterizations of the ice cover.

Comiso, J. C.↗
NASA NTRS1984

Sea Ice

Scientific objectives and observational requirements relative to sea ice studies in the 1990's are discussed. The development of coupled ice-ocean-atmosphere models that provide information comparable to real data sets through interactive processes is discussed. A series of particular problems that would provide the basis for such a verification data set and which is amenable to satellite systems available or realizable over the next 20 years is presented.

Ackley, S. F.↗
NASA NTRS1984

Antarctic sea ice microwave signatures and their correlation with in situ ice observations

The general characteristics and microwave radiative properties of sea ice in the Weddell Sea region during the onset of spring are studied by using the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and other satellite sensors, in conjunction with in situ observations from the Mikhail Somov. The position of the ice edge, the gradient of ice concentration, and the width of the Marginal Ice Zone are inferred from the microwave data, and are found to be consistent with ship observations, especially at 18 GHz. The sensitivities of the various SMMR frequencies to surface and other effects are investigated by using multispectral cluster analysis. The results show considerable variability in emissivity, especially at 37 GHz, likely associated with varying degrees of surface wetness. Ice concentrations are derived by using two methods: one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed. Using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations.

Comiso, J. C.↗
NASA NTRS1983

Numerical simulation of the Weddell Sea pack ice

In order to determine the degree to which a coupled dynamic thermodynamic model can reproduce the seasonal cycle of the Antarctic Sea ice in the Weddell Sea, a series of two-year simulations of the Weddell Sea ice pack were carried out. The simulations employed Hibler's (1979) model and used a one-day time step on an 18 x 15 grid with a resolution of 222 km. Daily atmospheric data from 1979 were used to drive the simulations. The simulations yielded a seasonal cycle of ice with maximum and minimum extents close to that observed. Except for portions of the western Weddell, the advance of the ice is found to be primarily thermodynamic in nature, while the rapid decay depends critically on the presence of both leads and lateral ice advection. In early summer the ice motion causes a residual tongue of ice to extend eastward from the Antarctic Peninsula in agreement with observations. Mean ice thicknesses are consistent with observations, as are the mean drift rates of about 5 km/day.

Hibler, W. D., III↗