BINARY INTERACTIONS BETWEEN POLAR LOWS

In this study, the movement of polar lows is addressed from a novel an d perspicuous viewpoint. The usual assumption has been that these meso scale systems are, to a first approximation, advected by the larger sc ale flow in which they are embedded. However, when there are two or mo re polar lows in the same vicinity, binary interactions between pairs of polar lows can cause a cyclonic co-rotation of the pair. In geograp hic coordinates these interactions can appear as unusual loops, twists and turns in the low tracks, due to the interplay between the cycloni c co-rotation and the translation of the binary pair by the ambient ho w. However when the tracks are replotted in centroid relative coordina tes, a mutual rotation is unmistakable. Satellite imagery from several case studies has been examined to accurately determine the polar low tracks, and thus the co-rotations. Using surface wind observations, a theoretical rotation rate can be estimated, based on barotropic vortex dynamics. There is a good correspondence between the observed and cal culated rotation rates. Recognizing the existence of binary interactio ns between polar lows emphasises the connection between polar lows and tropical cyclones, where binary interactions have been described in s everal studies. Indeed, in the cases studied here, binary interactions are strongest during the secondary (convective) stage of polar low de velopment where the lows are somewhat analogous to arctic hurricanes.