The occurrence of coreless winters in central Spitsbergen and their synoptic conditions
Ten warm-core winters were distinguished in the period 1975/76-2007/08, drawing on data from the Svalbard Airport weather station in central Spitsbergen and using the conditions tm-1 < tm and tm > tm+1 (t is the monthly mean temperature while m-1, m and m+1 denote subsequent winter months) and the parameter of a coreless rate, cr (the ratio of the second, a2, to the first, a1, harmonic of the annual temperature wave). Composite maps of sea-level pressure and z 500-hPa means, as well as anomaly maps, were constructed separately for the mid-winter warm events and for the cold months before and after warming. Using the clustering method, different pressure patterns were recognized among the days of mid-winter warm spells. The occurrence of coreless winters in central Spitsbergen seems to be largely controlled by the position, extent and intensity of large-scale atmospheric systems, mainly the Icelandic Low. When the low spreads to the east and its centre is over the Barents Sea the inflow of air masses from the northern quadrant is observed over central Spitsbergen. This inflow of cold air of Arctic origin to the island takes place during the months preceding and following warm mid-winter events. Different circulation conditions appear when the Icelandic Low gets deeper than usual and shifts northwards, which coincides with warm spells. Sometimes a secondary cyclonic centre is located over Fram Strait and its warm sector encompasses Svalbard.
Keywords: Spitsbergen; coreless winters; air temperature; circulation; polar climate
(Published: 13 December 2011)
Citation: Polar Research 2011, 30, 12218, DOI: 10.3402/polar.v30i0.12218
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