The thermal, anemometric and bioclimatic conditions on the topoclimatic scale were investigated in the summer season in the EbbaValley region in central Spitsbergen. Eight measurement sites, representing different ecosystems and different types of active surfaces typical of Spitsbergen, were chosen and automatic, hourly recorded, measurements were per− formed at the sites between 11 and 25 of July 2009. The analysis of the spatial distribution of the air temperature and thewind−chill temperature, both for the dayswith radiation and non−ra− diation weather, indicates that the most favorable regions in the interior of Spitsbergen are those situated in the shielded central parts of the valleys and in the lower parts of the slopes with southern exposure. The thermal and wind conditions are definitely less favorable at the tops of elevations and on the glacier. Large differences between the air temperature and the wind−chill temperature were noted, particularly during the unfavorable non−radiation weather, on the glacier and on open peaks due to a large horizontal and vertical wind−chill temperature gradient. The thermal inversions observed in the Ebba Valley in July 2009 were not of the typi− cal, glacier katabatic wind origin. They appeared during the western air circulation, which brings advection of cooled air from above the cold waters of Petunia Bay. The cold air pene− trates into the valley and pushes upwards themass of warmer air in the valley, creating a rather thin inversion layer, whose upper edge is marked with thin Stratus clouds.

The coreless winters ( i.e. not having a cold core) were distinguished in four stations within the European sector of the Arctic. Anomalies of the frequency of the Niedźwiedź’s (2011) circulation types were calculated separately for the mid−winter warm months and for cold months preceding and following the warm−spells. Furthermore, composite and anomaly maps of the sea level pressure as s well as anomaly maps of the air temperature at 850 gpm (geopotential meters) were constructed separately for the mid−winter warm events and for the cold months before and after warming. Different pressure patterns were recognized among the days of mid−winter warm spells, using the clustering method. The occurrence of coreless winters in the study area seems to be highly controlled by the position, extension and intensity of large scale atmospheric systems, mainly the Icelandic Low. When the Low spreads to the east and its centre locates over the Barents Sea the inflow of air masses from the northern quadrant is observed over the North Atlantic. This brings cold air of Arctic origin to the islands and causes an essential drop in the air temperature. Such situation takes place during the cold months preceding and following the warm mid−winter events. During the warm spells the Icelandic Low gets deeper−than−usual and it is pushed to the northeast, which contributes to the air inflow from the southern quadrant.

In this study, weather conditions causing warm waves in north−western Spits − bergen, exemplified by Ny− Å lesund station, were analyzed. Between 1981 and 2010, 536 days with the maximum temperature exceeding 8.3 ° C (the value of 95 percentile) were selected. 37 warm waves, which altogether lasted 268 days, were identified. A typical feature of pressure pattern causing warm waves was the appearance of positive anomalies of both the sea level pressure and the height of isobaric surface 500 hPa in the Euro−Atlantic sector of the Arctic. This indicates a presence of high−pressure systems in this region. Extremely warm days appeared more often with the circulation from the eastern than the western sector. Longer and warmer heat waves occurring in the last decade of the analyzed period may be considered as a sign of climate warming, which has a significant impact on environment, i.e. reduction in area and thickness of glaciers, reduction of permafrost and snow cover, changes in biodiversity, etc . The increase in the air temperature and more frequent occurrence of heat waves may encourage development of tourism in polar areas, potentially causing further changes in the environment.

Significant increasing trends in the air temperature were found both in the surface station of Svalbard Lufthavn and in the low-tropospheric temperature field over the Atlantic Arctic. The variability in temperature, as well as the multiannual trend, is at least three times bigger in the winter months than in summer. An attempt was made to explain the high day-to-day variability in the winter air temperature by the daily variability in the regional pressure field and circulation conditions. Six regional-scale circulation patterns were found by applying the principal component analysis to the mean daily sea level pressure (SLP) reanalysis data and their impact on the low-tropospheric air temperature variability was determined. A bipolar pattern, with a positive center over Greenland and a negative center over the White Sea, dominates in the region and strongly influences the air temperature field at 850 hPa geopotential height (correlation coefficients up to –0.65). The second pattern that impacts the temperature field in the Atlantic Arctic is the one with a center of action over Svalbard (mostly a low-pressure center in winter), strongly influencing the air temperature over the Barents Sea. The remaining circulation types, explaining only 5–8% of the total variance of the SLP field each, do not modify significantly the air temperature at 850 hPa geopotential level over the Atlantic Arctic, and none of the circulation types seems to influence the multiannual temperature trends.