83rd Annual

Thursday, 13 February 2003: 3:45 PM
A comparison of model output with SAR imagery of a polar low over the Labrador Sea
Rebekah Martin, University of Toronto, Toronto, ON, Canada; and G. W. K. Moore and P. Vachon
Polar lows are short-lived, intense mesoscale storm systems that develop over oceans in Polar Regions. The interaction of the very cold atmosphere with the relatively warm ocean below is what provides these storm systems with their intense energies. As a result of their small spatial and temporal scales, and their development in regions where observational coverage is minimal, models and observations can easily miss the genesis and lifetime of a polar low. It is for this reason that satellite imagery, and in particular Synthetic Aperture Radar (SAR) imagery, is a very important tool in the furthering of our understanding of these systems. SAR is an excellent way to image marine weather systems specifically because it can penetrate the dense cloud cover that accompanies these systems, and it can provide information to within a 100 m resolution about surface winds.

A polar low that was imaged by the RADARSAT-1 satellite on December 29, 1997 is simulated with the Penn State/NCAR fifth-generation Mesoscale Model (MM5). Model results of the near surface wind fields are compared to the SAR imagery from the satellite and are found to possess strikingly similar features. Specifically, the low wind speed eye of the storm and high wind speed fronts are apparent in both the SAR image and the model output. Comparison of observational data from Greenland and Baffin Island to model surface and upper air output provides a further check of the model performance. The model shows a deep low with near zero central wind speeds and maximum wind speed of around 25 m/s.

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