Polar low 'Le Cygne' over the Norwegian Sea October 13-16, 1993
A very interesting polar low development in the Barents Sea and the Norwegian Sea took place during 13th-14th October 1993. During the 15th it decayed slowly while moving southward outside the coast of Norway until it died out rapidly as it made landfall in Southern Norway in the morning hours the 16th. A satellite picture at a stage where the polar low was developing showed cloud forms that clearly justify the name "The Swan". Results from a numerical simulation of the development of the polar low using the NORLAMS are in a very good agreement with the results obtained from analysis of the satellite measurements. The overall setting prior to the development of the polar low is characterized by a synoptic scale low over Northern Scandinavia together with a ridge over the Greenland ice cap. The analyzed satellite measurements and the results of the numerical simulations indicate an initial strong low level baroclinic zone close to the ice edge in the Barents Sea where baroclinic instability seems to be released and where the static stability is low. At upper levels an outbreak of upper cold air is found with high values of potential vorticity above the baroclinic zone. Between this cold air outbreak and the low level air is a strong inversion which prohibits immediate interaction. When at a certain stage the baroclinic instability is sufficiently well developed, the interaction between the upper and lower systems causes the inversion to break down. The result is deep convection with organized cyclonic circulation, i.e. a "classic" polar low.
References:
Claud, C., Heinemann, G., Raustein E., Mcmurdie, L., 2004: Polar low 'Le Cygne': Satellite observations and numerical simulations. Quart. J. Roy. Meteorol. Soc. 130, 1075-1102.
Nielsen, N.W., 1997: An early Autumn polar low formation over the Norwegian Sea. J. Geophys.Res 102, 13955-13973.
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Copyright by Günther Heinemann.