Transition of a synoptic system to a polar low via interaction with the orography of Greenland

Abstract

A case study of a polar low that occurred over the Labrador Sea from December 29–31, 1997 was performed using the Penn State–NCAR Mesoscale Model version 5 (MM5). The polar low was imaged by the synthetic aperture radar (SAR) on the RADARSAT-1 satellite and as a result, unique high resolution information on the polar low’s surface expression is available. This low is also of interest as it formed from a synoptic-scale low pressure system that underwent a bifurcation through an interaction with the topography of Greenland. Our model results showthat the polar lowachieved a minimum central pressure of 954 hPa with maximum 10 m wind speeds in excess of 30 ms −1 . Coincident SSM/I data are in agreement with the model surface wind speed field. Sensitivity studies showed that the genesis of the low was relatively insensitive to air–sea fluxes of sensible and latent heat. The model precipitation field indicates the presence of features reminiscent of rainbands observed to occur in association with tropical cyclones, as well as frontal features typically seen in mid-latitude baroclinic systems. In addition, our model results indicate that precipitation as well as the surface wind contributes to the polar low’s surface expression as imaged by SAR.