Osobliwości klimatu Karkonoszy i Gór Izerskich

Climatic peculiarities of the Izera and Giant Mountains (Western Sudetes)

Summary: Orography and altitude play an important role controlling specific features of mountain climate. It is characterized by considerable spatial variability of topoclimatic conditions issuing from absolute and relative height, aspect and inclination of slopes, distance from surrounding mountain massifs and their size as well as shape, dimension and type of landform. The following factors are crucial to control climatic peculiarities of the Western Sudetes: exposure to advection of humid Atlantic air masses implied by position at the NW rim of the whole Sudetes ridge; the absence of other mountain massifs on the windward side and typical for the Izera Mts wide flat-bottomed concave landforms situated at relatively high altitude. One of the most interesting climatic curiosities is expressed by rapid and very deep nocturnal temperature drop at cloudless and calm nights during anticyclonic situations. So called "cold air lakes" situated at the bottom of flat valleys in the Izera Mts plateau is the result of negative radiation balance of land surface, gravity-induced drainage of cold air along slopes towards valley bottom and very poor flux of sensible heat from the ground. Since 1995 when temperature measurements (2 meters above the ground level) had been started at Hala Izerska, the lowest value was -36,8 °C on January 24st 2004 (Fig. 1). Low minima of air temperature are characteristic also the for vegetation period. In July 1996 temperature dropped to -5,5oC. The following unusual feature is extreme diurnal temperature range at Hala Izerska. The largest was observed on 24 February 2003 equal to 31°C and was not connected with any air mass change (Fig. 2). Due to distinct airflow deformation produced by a conspicuous landform situated on a windward side of the Sudetes, the highest annual precipitation at the scale of whole Sudetes exceeding 1500 mm are observed in the Izera Mts. Additional features of precipitation pattern are exceptionally high totals in the cool part of year and their quasi constant annual variations (Fig. 3). At three selected stations (Stóg Izerski, Orle and Hala Izerska - Fig. 1) average monthly precipitation exceeds 100 mm during the whole year. The main ridge of the Giant Mts. oriented WNW-ESE is perpendicular to prevailing wind directions. Because of their length and compact orography, the Giant Mts. are characterised by the highest wind speed in continental part of Europe. At Śnieżka (the highest summit, Fig. 1) and Szrenica (where Meteorological Observatory of the Wrocław University is situated) the average annual wind speed exceeds 12 and 9 ms-1 respectively (Tab. 1). It is much higher than at isolated and screened peaks like in the Alps or Carpathians where the air flows rather around the barrier than above - which is in contrast to the Giant Mts. Altitude, morphology, location related to circulation pattern, distance to sea, type of landform - favour occurrence of fog. A very good example of the role of these factors are Giant Mts. that show the number of days with fog near 300 per year (Fig. 4). It is the largest fog frequency in continental Europe. These facts (high wind speed and number of days with fog) make the Giant Mts. the area with huge additional water flux in the form of horizontal precipitation (Tab. 2). The efficiency of fog droplets deposition varies depending on size and surface area index of any receptor present. In the Izera Mts. the role of fog in total water flux could be locally greater than precipitation. Such situation is observed under trees at the edge of a spruce forest stand which belongs to the most efficient type of receptors. Summarising, the climatic conditions in the Western Sudety Mts. show great spatial variability. Paradoxically in some places of the Izera Mts. like flat-bottomed concave landforms situated on a mountain plateau, typical features of both maritime and continental climate are clearly visible. Maritime character of climate is expressed by relatively high sum of precipitation, high frequency of fog and its important role in a total water flux. On the other hand frequent and extremely intense inversions, very deep nocturnal temperature drop and extreme diurnal temperature range are observed there.

Słowa kluczowe: Góry Izerskie, Karkonosze, Sudety, zjawiska ekstremalne, klimat gór.

Krzemień K., Trepińska J., Bokwa A. (red.), 2005, Rola stacji terenowych w badaniach geograficznych, IGiGP UJ, Kraków, s. 109-121.

Instytut Geografii i Gospodarki Przestrzennej UJ

ISBN 83-88424-52-1

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