Accession Number : ADA298688

Title :   A Physically Based Model of the Form Drag Associated with Sastrugi,

Corporate Author : COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH

Personal Author(s) : Andreas, Edgar L.

PDF Url : ADA298688

Report Date : JUL 1995

Pagination or Media Count : 18

Abstract : On Ice Station Weddell, some characteristics of the neutral-stability-air-icedrag coefficient at a reference height of 10 m (C sub DNl0) were observed that had not been documented before. The main finding was that wind driven snow continually alters the sea ice surface; the resulting snowdrifts determine how large C sub DNl0 is. In particular, this report describes three observations and attempts to explain them: (1) C sub DNl0 is near 0.0015 when the wind is well aligned with the drifted snow; (2) C sub DN10 is near 0.0025 when the wind makes a large angle with the dominant orientation of the snowdrifts; (3) C sub DNl0 can increase by 20% if, after being well aligned with the drift patterns, the mean wind direction shifts by as little as 20 deg. To investigate this behavior of C sub DN10, this report adapts a model developed by Raupach that partitions the total surface stress into contributions from form drag and skin friction. With reasonable choices for free model parameters and with little fine-tuning, this physically based model can reproduce the three main observations. In other words, the model seems to include the basic physics of air-ice momentum exchange. This modeling implies that 10- cm-high sastrugi-like roughness elements, rather than pressure ridges, sustain most of the form drag over compact sea ice in the western Weddell Sea. Lastly, the report speculates on what the observations and this model say about how to parameterize C sub DN10 over snow-covered sea ice. (MM)

Descriptors :   *DRAG, *SEA ICE, *SNOWDRIFTS, ANGLES, OCEAN SURFACE, DISPLACEMENT, SURFACE ROUGHNESS, DRIFT, SNOW, COEFFICIENTS, SHIFTING, WIND VELOCITY, HEIGHT, SKIN FRICTION.

Subject Categories : Snow, Ice and Permafrost

Distribution Statement : APPROVED FOR PUBLIC RELEASE