Variations in Air-Ice Drag Coefficient

Objectives

To relate the variation in air-ice drag coefficient to ice surface roughness conditions, wind data were measured for 2 winters on the pack ice in the Gulf of St. Lawrence. It is expected that, even under constant wind conditions, various pack ice regions, with different surface roughness, experience different wind forcing and that ice pressure events within the pack ice do exist.

Ice beacons with anemometers at 2 m and 4 m heights.

Ice beacons with anemometers at 2 m and 4 m heights.

Ice-ocean modellers have tended to use constant values of drag coefficient which has been seen, from this experiment, to not always be appropriate. Variable drag coefficients for ice-ocean models that depend on the evolution of pack ice can be determined with the increasing capability of remotely-sensed imagery to classify ice types and ice roughness conditions.

Ice beacons with anemometers at 2 m and 4 m heights.

Ice beacons with anemometers at 2 m and 4 m heights.

Data Collection

Hourly wind profiles over various ice surfaces were collected by ice beacons deployed on the pack ice in the Gulf of St. Lawrence during the winters, from 1998-2000. Wind time series data from heights 0.6 m to 6.0 m were collected for 5 locations to relate the variation in air-ice drag coefficient C10 to surface roughness conditions measured by helicopter-borne instrumentation.

The Video Sensor System collected digital video images and laser/radar altimeter profiles with GPS positioning. This provided ice concentration, ice roughness, and ridge, floe, and lead distribution data.

Instruments

  • satellite-tracked atmospheric ice beacons built by MetOcean Data Systems Ltd. of Dartmouth, N. S.
  • atmospheric ice beacon built at BIO
  • Video-Laser-GPS Sensor System

Results

Wind speed regression plots for 2 m versus 6 m observation pairs.  Derived C<sub>10</sub> values are listed along with value used by forecast models.

Wind speed regression plots for 2 m versus 6 m observation pairs. Derived C10 values are listed along with value used by forecast models.

Related Projects

Related Publications

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  • Prinsenberg, S. J. and I. K. Peterson. 2001. "Variations in Air-Ice Drag due to Ice Surface Roughness"
  • Prinsenberg, S. J. and I. K. Peterson. 2002. "Variations in Air-Ice Drag due to Ice Surface Roughness"
  • van der Baaren, A. and S. J. Prinsenberg. 2001. "Satellite-tracked Ice Beacon Program, 1999-2001"