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  • Author or Editor: Konrad Steffen x
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Konrad Steffen
and
Ted deMaria

Abstract

The surface energy balance of sea ice was measured during degree one-week periods in November, January, and February of 1980–81 in the Barrow Strait, Northwest Territories, Canada. Turbulent fluxes were derived with the bulk aerodynamic transfer method, using temperature, dewpoint, and wind speed profile measurements. The conductive heat flux was balanced by the sensible and latent heat fluxes, and by the radiative fluxes for all three measuring periods. In November, when there was a mean ice thickness of 0.32 m, approximately 80%, ±6% of the conductive heat flux (− 129 W m−2) was dissipated by the sensible heat flux (108 W m−2), approximately 20% ± 8% of the energy was lost by longwave radiation (30 W m−2), and the latent heat flux (6 W m−2) accounted for 4% of the total surface energy balance. Ice growth rates could be predicted for young ice with an accuracy of 10%, based on conductive flux measurements. Brine-wetted snow on sea ice increased the conductive heat flux to two Lorries that of pure snow. In January, when there was a mean ice thickness of 0.92 m, approximately 50% ± 9% of the conductive heat flux (−50 W m−2) was dissipated by sensible heat flux (26 W m−2), approximately 50% ± 9% was dissipated by radiative cooling (27 W m−2), and the latent heat flux had a mean value of 0 W m−2. Variations in the surface energy balance tend to be related to synoptic events, such as the horizontal advection of warm air and the increased cloudiness of transient eddies. In February, the mean conductive heat flux was −36 ± 4 W m−2, which was balanced by the radiative flux of 32 ± 2.5 W m−2 (80% ± 8%) and by the sensible flux of 10 W m−2 (20% ± 6%). Again, large-scale synoptic events dominated the surface energy balance. On a weekly basis, the mean surface energy balance residuals were within the predicted uncertainties, based on instrument resolution.

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Julienne Stroeve
and
Konrad Steffen

Abstract

The Advanced Very High Resolution Radiometer is used to derive surface temperatures for one satellite pass under clear skies over the Greenland ice sheet from 1989 through 1993. The results of these temperatures are presented as monthly means, and their spatial and temporal variability are discussed. Accuracy of the dry snow surface temperatures is estimated to be better than 1 K during summer. This error is expected to increase during polar night due to problems in cloud identification. Results indicate the surface temperature of the Greenland ice sheet is strongly dominated by topography, with minimum surface temperatures associated with the high elevation regions. In the summer, maximum surface temperatures occur during July along the western coast and southern tip of the ice sheet. Minimum temperatures are found at the summit during summer and move farther north during polar night. Large interannual variability in surface temperatures occurs during winter associated with katabatic storm events. Summer temperatures show little variation, although 1992 stands out as being colder than the other years. The reason for the lower temperatures during 1992 is believed to be a result of the 1991 eruption of Mount Pinatubo.

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Julienne Stroeve
,
Marcel Haefliger
, and
Konrad Steffen

Abstract

The relationship between Along Track Scanning Radiometer (ATSR) thermal radiances and snow surface temperature for the Greenland ice sheet is examined through forward calculations of the LOWTRAN 7 radiative transfer model. Inputs to the model include in situ radiosonde profile measurements of temperature, pressure and humidity, surface temperatures, and cloud observations for spring-summer 1990 and 1991 from the ETH-CU research camp, located at 69°34′N, 49°18′W on the Greenland ice sheet. Atmospheric correction coefficients were determined through a statistical analysis of daily clear-sky profiles for three different combinations of the ATSR thermal infrared (TIR) channels. Using all available ATSR TIR information, the 11- and 12-μm channels in both the nadir and forward views showed the smallest rms error of less than 0.2 K in the estimated surface temperature. This dual-view algorithm was found to be least sensitive to changes in concentrations of atmospheric constituents, in contrast to the standard “split-window” technique. Assuming accurate surface emissivities can be obtained, the dual-view algorithm is recommended for applications in polar regions where the variety of atmospheric conditions can be large.

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Christopher A. Shuman
,
Konrad Steffen
,
Jason E. Box
, and
Charles R. Stearns

Abstract

On 4 May 1987, the first automatic weather station (AWS) near the summit of the Greenland Ice Sheet began transmitting data. Air temperature records from this site, AWS Cathy, as well as nearby AWS at the Greenland Ice Sheet Project II (GISP2, now Summit) camp have been combined with Special Sensor Microwave Imager brightness temperature data to create a composite temperature history of the Greenland summit. This decadal-plus-length (4536 days) record covers the period from May 1987 to October 1999 and continues currently. The record is derived primarily from near-surface temperature data from AWS Cathy (May 1987–May 1989), AWS GISP2 (June 1989–November 1996), and AWS Summit (May 1996 and continuing). Despite the 35-km distance between them, the AWS Cathy data have been converted to the equivalent basis of temperatures from the AWS GISP2 and AWS Summit locations. The now completed “Summit” temperature time series represents a unique record that documents a multiyear temperature recovery after the eruption of Mt. Pinatubo in June 1991 and that initiates a baseline needed for climate change detection.

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