Ewa Łupikasza

Recent warming on Spitsbergen—Influence of atmospheric circulation and sea ice cover

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.

Change in Atmospheric Circulation Patterns

This chapter examines both variability and trends in atmospheric circulation favouring the occurrence of flood precipitation defined as daily totals ≥30, ≥50 and ≥100 mm in warm half-year (May–Oct) and in summer (JJA). We used a catalogue of circulation types created for the Upper Vistula Basin, and related circulation indices (zonal circulation index, meridional circulation index, cyclonicity index and NAO) covering the 1874–2015 period. Climatology of atmospheric circulation over the Upper Vistula Basin is discussed as a basis for further investigations. In order to select circulation types and indices impacting both the occurrence and long-term variability of flood precipitation, we calculated the frequency and conditional probability of high precipitation (≥50 mm) in circulation types and correlation between selected circulation characteristics and high precipitation frequency (≥30 mm). Trends in the frequency of circulation types and indices favouring the occurrence of high precipitation were calculated to assess current and possible future flood conditions. In summer and warm half-year the Upper Vistula Basin was usually under an influence of anticyclonic wedge (Ka circulation type) and cyclonic trough (Bc circulation type). Circulation types with the air flow from the west (Wa and Wc) were the most frequent of all advectional types. The occurrence and long-term variability in flood precipitation over the Upper Vistula Basin were strongly linked to the frequency of air advection from the north and north-east under an influence of low pressure system (Nc and NEc circulation types) and to Wi—zonal circulation index at both stations in summer (JJA) and to Ci—cyclonicity index at Kasprowy Wierch station in warm half-year (May–Oct). Trends in majority of circulation characteristics favouring the occurrence of high precipitation and impacting its long-term variability were not statistically significant with an exception of the frequency of Nc type and Ci index in the warm half-year and Wi index in summer. Significant increase in the number of days with Nc circulation type and the cyclonic situations (Ci index) in warm half-year and intensification of air advection from the north-east in summer may lead to increase in the frequency of flood conditions in these seasons. Regardless insignificant trends, the variability in the NEc frequency considerably determines the occurrence and long-term variability of high precipitation thus was recognized as indicator of flood conditions. There was intensification of the air advection from the north (Nc) in the warm half-year (May–Oct) in the 50-year period between 1930 and 1980. High frequency of NEc type was found in seventies and eighties which coincided with the high frequency of floods in those decades in Poland and at the turn of the first and second decades of the 21st century. Low frequencies of these circulation types during 1982–1995 were in phase with relatively dry conditions in Southern Poland without the floods within the Upper Vistula Basin. In the further more wet years the great floods happened in July 1997 and May 2010.

FREQUENCY OF ICE DAYS AT SELECTED METEOROLOGICAL STATIONS IN SVALBARD

Abstract The paper aims to present research into both the long-term variability in the ice days in Svalbard representing the Atlantic sector of the Arctic, and their relations to atmospheric circulation. Ice days are defined as days with a daily maximum temperature below 0°C (Tmax<0°C). They are considered to be amongst the most important indices of current climate change. All the available data on daily maximum air temperature from three Norwegian stations (Svalbard Airport (Svalbard Lufthavn), Bjørnøya and Hopen) and from the Polish Polar Station in Hornsund (SW Spitsbergen) have been employed. The relevance of atmospheric circulation to the frequency of the occurrence of ice days was evaluated by calculating the Spearman correlation coefficients between the frequency of ice days and three regional circulation indices: zonal westerly circulation index (W), meridional southerly circulation index (S) and index of cyclonicity (C). At all the stations the number of ice days exhibited significant decreasing trends in the period of 1979-2012.

Long-term variability of occurrence of precipitation forms in winter in Kraków, Poland

The paper discusses long-term change in snowfall, rainfall and mixed precipitation viewed in conjunction with air temperature and North Atlantic Oscillation (NAO) in winter (December–February). In the study of contemporary climate change and its effect on the hydrological cycle it is useful to focus on winter precipitation forms. A 146-year secular observation series from Kraków, spanning the period 1863–2008, was used to extract data on the number of days with precipitation and on precipitation amount broken down by form. Statistically significant trends were found in total and mixed precipitation, but not in snowfall and rainfall. The climate warming effect has contributed to a material decrease in the snowfall to total winter precipitation ratio during the second half of the 20th c. The highest impact of air temperature was found in the wintertime variation in number of days with snowfall while the NAO had a significant influence on the frequency and amount of both rainfall and snowfall.

Observed Changes in Air Temperature and Precipitation and Relationship between them, in the Upper Vistula Basin

The chapter presents changes in air temperature and precipitation in the Upper Vistula Basin. Data from 18 meteorological stations covering the 1951–2015 period was used to investigate variability and trends in air temperature, precipitation and linkages between them. Air temperature in the Upper Vistula Basin was significantly rising during the research period. Distinct warming on annual scale started in the first half of the eighties. Spring and summer air temperatures have been significantly increasing; winter air temperature trends were much weaker while no significant changes were found in autumn. Upward trends in air temperature within the Upper Vistula Basin were also reflected in the frequency of thermally characteristic days which was significantly changing during the research period. Strong downward trends were found in the frequency of winter days (Tavg ≤ 0 °C) while trends in warm characteristic days were positive. Most observed changes in precipitation were not statistically significant at the level of 0.05. This indicates that significant increase in air temperature is not currently accompanied by significant increase in precipitation thus changes in precipitation are not directly related to changes in air temperature and they possibly vary in time. Relations between precipitation and air temperature are not straightforward. The results indicate that strong increase in air temperature is rather accompanied by decrease in precipitation frequency and amount. However, this applies only to overall precipitation totals and not to extreme events which are random and can occur unexpectedly. Flood precipitation can also occur during drier periods, as in the last decade of the research period. It however must be mentioned that for nearly all stations mean precipitation totals from the warmer period of 1991–2013 (1991–2011) were higher than in previous period 1961–1990. Moreover the study revealed that increasing, statistically significant, trend (from 0.15 to 0.24 °C/decade) in mean annual air temperature likely impacted changes in heavy precipitation. The links between air temperature ranges (0–10, 10–20 °C and above 20 °C) and precipitation ranges (0–10 mm, 10–20 mm, etc. to above 50 mm) for two periods examined at nine stations in the Upper Vistula Basin revealed that when air temperature exceeded 20 °C more intense precipitation was observed in the second warmer period 1991–2013.

Regional Differentiation in Probability of Ice Days Occurrence in Poland

Abstract This paper aims at recognizing spatial differentiation in probability of ice days occurrence with reference to atmospheric circulation, using regional classification of circulation types for Poland. Daily maximum air temperatures measured at nine meteorological stations were used to recognize the ice days occurrence in the period from January 1951 to March 2014. The relations between the ice days occurrence and atmospheric circulation were analysed using catalogues of circulation types compiled for nine grid boxes within Poland. Linkage between the frequency of ice days and atmospheric circulation was recognized in the period of January 2001 - March 2014. A decreasing tendency in the frequency of the occurrence of winter ice days was found. The occurrence of ice days in Poland is clearly related to atmospheric circulation. In the entire area of Poland their occurrence is favoured by eastern and south-eastern advection of air during anticyclonic conditions (types Ea nad SEa). Regional variability is also noticeable.

Changes of flood risk on the northern foothills of the Tatra Mountains

The present paper reviews selected outcomes of the FLORIST project devoted to flood risk in the region of the northern foothills of the Tatra Mountains in Poland and summarizes novel results. The project encompassed theoretical, field, and modeling work. It was focused around observation-based hydroclimatology; projections for the future; dendrogeomorphology; as well as influence of transport of large wood on fluvial processes. The project improved understanding and interpreting changes in high-flow frequency and magnitude as well as changes in flood risk in the region, related to the presence of large wood in mountain streams. A unique database on past episodes of intense precipitation and flooding was created, harnessing multiple sources. The project showed that the analysis of tree rings and wood logs can offer useful information, complementing and considerably enriching the knowledge of river floods in the region of northern foothills of the Tatra Mountains. Retrospective and scenario-defined modeling of selected past fluvial events in the region was also performed.

Variability of Flood Frequency and Magnitude During the Late 20th and Early 21st Centuries in the Northern Foreland of the Tatra Mountains

Much of the flood risk in Poland is related to the Upper Vistula River Basin, and its right-bank tributaries on the northern foreland of the Tatra Mountains significantly contribute to the total flood damage. Therefore, the question whether the magnitude and frequency of floods in this region have changed in the past decades is of high interest. This chapter focused on the inter-decadal variability of magnitude, frequency, and seasonality of floods since the mid-20th century using a multi-temporal approach in which trends are fitted to several combinations of start and end years in a record. The correlation between flood parameters and different large-scale climate indices for the Northern Hemisphere was calculated, as well as trends of intense precipitation indices, number of days with snow cover, cyclonic circulation types, air temperature and moisture conditions were calculated to explain the detected trends. Other potential external drivers, such as catchment and channel changes were also considered. Results show that floods in the area exhibit considerable inter-decadal variability, however, certain patterns are apparent. Less frequent floods, although perhaps more extreme, are now likely to occur, with a shift in the seasonality, decreasing flood magnitudes in winter and increasing during autumn and spring.

Definitions and Indices of Precipitation Extremes

Definitions of extreme climatological and meteorological events may depend on the objective of the study, the type of data, or the researcher’s subjective opinion. This chapter discusses definitions of extreme climatic events and presents indices of precipitation extremes found in the literature. The spatial and seasonal variability in a range of these indices were analysed, and the results were used to select criteria for identifying extreme precipitation in Europe adopted in this study. These criteria were then applied in subsequent chapters. During the study period, the maximum daily precipitation totals in Europe ranged from 37.6 to 520 mm. An overwhelming majority of stations (89 %) recorded daily precipitation greater than 50 mm less than once per year. Because there is great variability between precipitation regimens in Europe, this study adopted a statistical definition of extreme precipitation events. The events were identified separately for each of the weather station and in each of the months using an empirical distribution of the daily precipitation totals. Precipitation totals exceeding or equal to the 95th percentiles of daily precipitation were selected as extreme. The 95th percentile (95P) was calculated from days with daily totals ≥1 mm during the period 1961–1990. The resulting spatial and seasonal variability of the threshold values corresponding to the 95P daily precipitation across Europe is similar to the spatial and seasons variability of the monthly totals.

Synoptic climatology of fog in selected locations of southern Poland (1966–2015)

Abstract. This paper investigates fog frequency in southern Poland in relation to various relief (concave and convex) and atmospheric circulation types. It also discusses long-term variability in the annual and seasonal number of days with fog. Daily information on fog occurrence was taken from three high quality synoptic stations representing various landforms: Krakow-Balice (bottom of the hollow), Katowice-Muchowiec (Silesian Upland) and Bielsko-Aleksandrowice (summit of Carpathian Foothill). In the central part of southern Poland during the last 50 years (1966-2015) fog occurred on average during 53-67 days a year. The annual number of foggy days in Krakow (67 days) located in a structural basin was by 14-15 days higher than in Bielsko (53 days) situated in the Silesian Foothill. In annual course high fog occurrence (above 6 days per month) was observed from September to January with maximum in Krakow (10 days in October). The monthly minimum of fog occurrence in all stations fell on July (2 days). In summer and spring the highest probability of fog occurrence was found at days with anticyclonic types and air advection from the northeastern (Na, NEa) and eastern (Ea, SEa) sectors. In autumn the high probability was also found for the anticyclonic types with advection of air mass from the eastern and southern sectors. In the Carpathian Foothill (Bielsko) the probability of fog occurrence in summer and winter was significantly enhanced only for the cyclonic types with air advection from the eastern sector (NEc, Ec, SEc) and nonadvective types Cc (cyclone center) and Bc (cyclonic trough). Fluctuations dominated in the long-term course of fog frequency. The only significant trend was found in Krakow on annual scale and in summer when fog frequency was little.