Spitsbergen has experienced some of the most severe temperature changes in the Arctic during the last three decades. This study relates the recent warming to variations in large‐scale atmospheric circulation (AC), air mass characteristics, and sea ice concentration (SIC), both regionally around Spitsbergen and locally in three fjords. We find substantial warming for all AC patterns for all seasons, with greatest temperature increase in winter. A major part of the warming can be attributed to changes in air mass characteristics associated with situations of both cyclonic and anticyclonic air advection from north and east and situations with a nonadvectional anticyclonic ridge. In total, six specific AC types (out of 21), which occur on average 41% of days in a year, contribute approximately 80% of the recent warming. The relationship between the land‐based surface air temperature (SAT) and local and regional SIC was highly significant, particularly for the most contributing AC types. The high correlation between SAT and SIC for air masses from east and north of Spitsbergen suggests that a major part of the atmospheric warming observed in Spitsbergen is driven by heat exchange from the larger open water area in the Barents Sea and region north of Spitsbergen. Finally, our results show that changes in frequencies of AC play a minor role to the total recent surface warming. Thus, the strong warming in Spitsbergen in the latest decades is not driven by increased frequencies of “warm” AC types but rather from sea ice decline, higher sea surface temperatures, and a general background warming.

ABSTRACT:The study investigated spatial and temporal variability of extreme precipitation trend magnitudes and their directions. Daily precipitation from 48 synoptic stations in Poland for the period 1951-2006 were used. Five indices of precipitation extremes were chosen: the highest 5-day precipitation total, precipitation total from events ≥90 th and 95 th percentiles as well as number of days with precipitation ≥90 th and 95 th percentiles of daily precipitation amount. Trends in extreme precipitation indicators were analysed over semi-annual periods as well as over the standard climatological seasons. Trends were calculated for each of the 30-year moving periods within 1951-2006 using a simple linear regression method. Their significance was tested with the Mann-Kendall method.Decreasing trends in extreme precipitation indices dominated in both the warm and cool halves of the year and in the seasons. The greatest change was recorded in the least extreme precipitation indices. Summer was the season with the greatest number of statistically significant trends, mostly decreasing ones. Upward trends, having the greatest spatial extend in autumn, dominated the initial 30-year periods of the study period whereas the decreasing trends were common in the 30-years from 1956. In summer and winter, decreasing trends reached the greatest degrees of stability in southern Poland. In spring and autumn, a stable fall of extreme precipitation indices was mainly recorded in the south-western part of the country. Stable increasing trends were recorded sporadically. However, in spring trends towards an increase were more frequent than in other seasons. The strongest decreasing trends were observed in summer and winter, mainly in the south, while in autumn they also occurred in the west.

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The Svalbard Airport composite series spanning the period from 1898 to the present represents one of very few long-term instrumental temperature series from the High Arctic. A homogenized monthly temperature series is available since 2014. Here we increase the resolution from a monthly to daily basis, and further digitization of historical data has reduced the uncertainty of the series. The most pronounced changes in the 120-year record occur during the last three decades. For the 1991–2018 period the number of days warmer than 0 and 5 °C has increased by 25 (21%) and 22 (59%), respectively, per year compared to the 1961–1990 standard normal. Likewise, comparing the same periods, the number of days colder than −10 and −20 °C has decreased by 42 (32%) and 27 (62%), respectively. During the entire time span of the series, the western Spitsbergen climate has gone through stepwise changes, alternating between cold and warm regimes: 1899–1929 was cold, 1930–1961 warm, 1962–1998 cold and 1999–2018 warm. The latest cold regime was 1.0 °C warmer than the first cold one, and the latest warm regime was 1.7 °C warmer than the previous warm one. For the whole series the linear trend for annual means amounts to 0.32°C/decade, which is about 3.5 times the increase of the global mean temperature for the same period. Since 1991, the rate of warming at Svalbard Airport is 1.7 °C/decade, which is more than twice the Arctic average (0.8 °C/decade, north of 66 °N) and about seven times the global average for the same period.

Spatial and temporal trend variability in extreme precipitation indices was studied for the meteorological seasons from 1951 to 2006. Eight indices were used, describing their frequency (90pNoD, 95pNoD), totals (1dayT, 5dayT, 90pT, 95pT) and intensity (90pInt, 95pInt). The following key challenges were addressed: (1) temporal variability in the relative number of stations with significant 30-year trends, (2) temporal stability and (3) average magnitude of the calculated 30-year trends. Temporal changes in the spatial extent of statistically significant extreme precipitation trends proceeded differently in each season. The trend direction, indicated by trend stability analysis, was consistent with that of averaged 30-year trend magnitudes at most stations. A distinct spatial differentiation emerged in the prevailing trend directions between the eastern and the western part of the study area. In all seasons, increasing trends in extreme precipitation dominated in central-eastern Germany, whereas opposite trends prevailed in southern Poland. This pattern was particularly prominent in winter. Similarities in the temporal variability of the percentage of significant trends between the eastern and the western sub-regions emerged in autumn only. Summer was characterized by the most pronounced temporal changes in the percentage of significant negative trends. Summer also showed the most stable extreme precipitation trends of all seasons and a higher trend magnitude than the transitional seasons. Spatial patterns of trend directions in spring, showing the most complex pattern of all seasons, vary depending on the index, particularly with respect to trend stability.

This contribution provides the basics of the climatology of the Polish Tatra Mountains in a nutshell, with particular reference to intense precipitation and its relation to atmospheric circulation. Variability of various precipitation characteristics, including selected indices of intense precipitation in Zakopane and at Kasprowy Wierch, is illustrated in this paper. None of the trends in these characteristics and indices calculated for the entire time interval exhibit a statistical significance, but short-time fluctuations are evident. The occurrence of intense precipitation in the Tatra Mountains is strongly related to three circulation types. These situations (Nc, NEc, Bc) are associated with cyclones following track Vb after van Bebber. In addition to changing frequencies of circulation, this study also reveals an increase in the frequency of the circulation types associated with extreme precipitation.

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The paper discusses the impact of atmospheric circulation on the occurrence of various types of precipitation. A 146-year-long precipitation record from Kraków spanning the period 1863-2008 was used alongside a calendar prepared by Niedźwiedź (1981Niedźwiedź ( , 2009) describing circulation types covering the period 1873-2008 and air masses and atmospheric fronts covering the period 1951-2008 in southern Poland. The influence of atmospheric circulation on precipitation was measured using the frequency, conditional probability and average daily totals of precipitation. Circulation types, air masses and atmospheric fronts exerted influences on precipitation as a result of the seasonal variations of the thermal and moisture properties of air masses. The impact is best expressed by circulation types as these combine the aspect of cyclonicity/anticyclonicity with that of the direction of air advection, the two elements which determine the physical properties of the air. On average, liquid precipitation prevailed in all circulation types, except the Ea type in which snowfall dominated over liquid precipitation. Depending on the season, one of the three types of circulation, Wa, Wc and Bc, were shown to coincide with the greatest amount of liquid and thunderstorm precipitation. There was no single dominant circulation type for mixed precipitation or snowfall. In summer, the circulation types Nc, NEc, Cc and Bc were the most favourable to liquid and thunderstorm precipitation in terms of both probability and totals. In winter, snowfall was the most favoured by the Ec type. Frontal precipitation was twice as likely to occur as air mass precipitation, with the exception of snowfall which was predominantly an air mass type of precipitation in terms of probability, but its greatest totals were recorded on atmospheric fronts.