Long-term variability of extreme precipitation in Hornsund (Spitsbergen) and their relation with atmospheric circulation

Celem opracowania jest określenie charakterku wieloletnich zmian i zmienności ekstremów opadowych w okresie obserwacji instrumentalnych w Hornsundzie oraz zbadanie synoptycznych przyczyn ich występowania. Badania przeprowadzono na podstawie dobowych sum opadów atmosferycznych z okresu lipiec 1978 – grudzień 2006. Za ekstremalne zjawisko opadowe uznano dobową sumę opadów przekraczającą wartość progową opadu, zdefiniowaną jako 90 i 95 percentyl. Ogólne tendencje w przebiegu czasowym wskaźników opadów ekstremalnych zbadano stosując analizę trendów metodą Mann-Kendala. Związki pomiędzy ekstremal-nymi zdarzeniami opadowymi i cyrkulacją atmosferyczną zbadano poprzez obliczenie częstości opadów ekstre-malnych oraz prawdopodobieństwa warunkowego ich wystąpienia w poszczególnych typach cyrkulacji według T. Niedźwiedzia.Exploration of the long-term variability of precipitation extremes and its connections with atmo-spheric circulation is the main goal of this study. Daily precipitation total for the period July 1979 – December 2006 measured at Hornsund station located at West coast of Spitsbergen as well as calendar of circulation types for Spitsbergen (Niedźwiedź 2006) were used. Extreme precipitation was defined as days with precipitation above the 90th and 95th percentile calculated based on days with precipitation >0.1mm and >1.0 mm in the period 1979–2005. Several indices of precipitation extremes, describing its frequency, amount and share in the overall total were calculated for year, accumulation period (September-May), both warm (April-September) and cold (October-March) half-years and submitted to further analysis. In order to research the general trends of extreme precipitation indices Mann-Kendal method was applied. Relation between extreme precipitation characteristics and atmospheric circu-lation were investigated by analysis of frequency of extreme precipitation and conditional probability its occurrence at each of circulation types used. The most significant trends were noted in the case of share of extreme precipitation in overall precipitation totals whereas annual as well as accumulation period values of extreme precipitation indices were characterized by the most permanent trends. No statistically significant tendencies of extreme precipitation were observed for its warm half-year values. All indices of precipitation extremes show decreasing tendency from 1979 to the middle of the eighties. Clear increasing tendencies of the number of days with extreme precipitation, extreme precipitation total as well as its share in overall precipitation totals fall on the second half of the eighties and on the nineties. Weak decreasing tendencies of the annual values of extreme precipitation indices as well as their values for accumulation period and cold half-year were observed at the end of the 20th century and at the beginning of the new century (21st). Opposite direction of the extreme precipitation trends within the period mentioned above were only noted in the cold half-year. In the long-term variability of the extreme precipitation in Hornsund two sub periods (1979-1993 and 1994-2006) different in the averages values of the extreme precipitation indices can be pointed out. Extreme precipitation is the most probable at SWc synoptic situation in the warm half year whereas in the cold half-year extreme precipitation occurs with the highest probability at southern inflow of air masses at cyclonic situation (Sc). 10

Variability in the occurrence of rain and snow at Hornsund over the period July 1978 - December 2002

In the polar regions, the sums of precipitation of the accumulation period is of great importance, because they are an component one of the most valid processes connected with glacier mass balance - accumulation. From glaciological point of view, to determine which part of annual sums of precipitation appears in the form liquid and mixed and solid precipitation is the crucial problem. In this connection, the main aim of this paper is analyse variability of the precipitation with respect of their form in the annual course as well as their long-term variability in Hornsund in the period of 1978-2002. The data used in this article are mainly derived from meteorological yearbook Hornsund (2000, 2001) that was published by Institute of Meteorology and Water Management - maritime department in Gdynia and from yearbook Meteorological Conditions Hornsund, Spitsbergen (2001) that was published by Polish Academy of Science in Warsaw. Collected numerical data are not complete. There is a lack of data concerned precipitation sums and meteorological phenomenon for the period from 01sth to 26sth of July 1981. Moreover the data describing precipitation sums does not exist for the days: 04, 07, 09, 19 July 1979. In this article three main form of precipitation (liquid, mixed and solid) were considered. The form of precipitation was determined on the base of meteorological phenomenon that was recorded as current and last weather. The average, maximum and minimum daily air temperatures were additional criterions. In this connection that the notation of meteorological data prevented to consider each event of appearance of precipitation, the days with individual form of precipitation were subjected to analysis. The day with mixed precipitation means that during all 24 hour period (from 6 given to 6 next day) appeared one time snow and second time rain or snow and rain in the same time. The annual course of individual form of precipitation and their probability of appearance in each month, long term variability of sums of individual form of precipitation and the number of days with this form of precipitation in the accumulation and annual periods were discussed. The linear trends and variability coefficients were calculated for long term characteristics of precipitation. It was stated that in Hornsund long-term average sum of annual precipitation amounted at about 424 mm The greatest part of this appear in the liquid (37%) and the lowest in a mixed form. On average in Hornsund there is noted at about 239 days with precipitation in year from what 63% falls on days with snow and 13% on days with snow and rain. In the accumulation period the solid precipitation were characterized by greatest sums as well as greatest number of days with this one. Long-term course of individual form of precipitation shows similar tendencies. In the annual period as well as in the accumulation this one liquid precipitation are characterized by the highest variability coefficient and range of change. Their lowest sums occur in the middle of 80ies and from mid-80ies they show increasing tendency. Mixed precipitation shows the smallest range of change, their highest sums occur in the middle of 80ies and in the case of annual period also in the second half of 90ies. From the second half of 90ies mixed precipitation show decreasing tendency. Statistically significant increasing tendencies of liquid and mixed precipitation during all considered period accompany decreasing tendency of solid precipitation. The highest sums of solid precipitation occur in the first half of 80ies and the lowest one in the second half of the same decade. From the beginning of 90ies there is a decreasing tendency in the course of solid precipitation. During all considered period the solid precipitation dominate as regards number of days with precipitation. The number of days with solid precipitation until the end of 80ies was greater and in the 90ies was lower than long-term average

Features of the precipitation changesover the Svalbard in the annual cycle

This article discusses the changes in an annual cycle of precipitation observed over many years in the Svalbard area. Monthly precipitation sums recorded at the Isfjord Radio station, Björnöya, Jan Mayen were used to accomplish the analysis. Data presented come from GHCN (Vose et al. 1997), MCDW (1957-1997) and WWR (1929,1944,1947,1959,1968,1979,1981, 1987, 1994, 19(5). The characteristics of the annual precipitation were described using Wilgat's indicator of periodicity of precipitation ( 1949) and Vemic's pluviometric coefficient (Szreffel 1961). Apart from that the amount of the highest and the lowest occurrence of precipitation in each month was calculated during the 10-years moving periods. In addition the annual change of the monthly sums of precipitation was characterised. The analysis of the annual change of the periodicity indicator has proved that during the examined period the precipitation regime on Isfjord Radio station and Jan Mayen do not show clear changes. On Björnöya station from the mid forties periodicity of precipitation has decreased. On all examined stations until the late thirties the value of the pluviometric coefficient were less than 50%. Since the mid forties over half of the amount of precipitation occurred from March to November. The highest sums of precipitation most often occurred in April, May and June. The highest sums of precipitation on Jan Mayen station and Björnöya station occurred mainly in September and October. On Isford Radio station the highest sums of precipitation were recorded chiefly in March. September. February and August

The long-term variability of precipitation in the Atlantic sector of the Arctic

In this study the multiyear variability of the annual and seasonal sums of precipitations in the Atlantic sector of Arctic were studied. The analysis were caried out on the base of 8 meteorological stations localized above the 60O N of latitude. The meteorological data were mainly obtained from GHCN (Peterson T. C et. all 1998) and NACD (Frich P. et. all., 1996). It was stated that at the large majority of the meteorological stations the greatest part of annual sums of precipitation appear in autum and the lowest one in spring. The annual as well as seasonal sums of precipitation were distinguised by considerable variation but their 5-years running of standarized value hardly ever exceeded 1 standard deviation. The coefficients variability counted in the running 11-years periods indicate on decrease of variability of the annual sa well as sprinf and winter sums of precipitation in the greatest part of Atlantic sector of Arctic

Dependence of precipitation forms on air temperature in Hornsund (Spitsbergen) in the period 1978-2007

Opracowanie dotyczy związków pomiędzy występowaniem różnych rodzajów opadu atmosfe-rycznego (ciekły, mieszany, stały) i temperaturą powietrza w Hornsundzie w okresie od lipca 1978 do grudnia 2007. Częstość oraz prawdopodobieństwo wystąpienia różnych rodzajów opadu określono w przedziałach śred-niej dobowej temperatury powietrza. Ponadto analizowano zależność liczby dni z rodzajami opadu od średniej miesięcznej temperatury oraz związki pomiędzy wieloletnią zmiennością liczby dni z poszczególnymi rodzajami opadu i średnią dobową, maksymalną i minimalną temperaturą powietrza w porach roku. Wysokie prawdopodobieństwo opadów ciekłych przypada na zakres średniej dobowej temperatury powietrza w granicach od 3.0°C do 7.0°C. Opady stałe występują najczęściej przy temperaturze od 0.0°C do –11.0°C. Dni z opadem ciekłym stanowią od 80 do 100% wszystkich dni z opadem w miesiącach ze średnią temperaturą .4.0°C, natomiast nie pojawiają się nigdy kiedy średnia miesięczna temperatura spada poniżej –13.0°C. Dni z opadem stałym stanowią od 80 do 100% liczby dni z opadem w miesiącach ze średnią temperaturą .–10.0°C. Opady ciekłe w dniach z temperaturą <0.0°C zdarzają się sporadycznie (przeciętnie raz w roku). Opady śniegu w dniach z temperaturą średnią powyżej 0.0°C notowane są średnio 14.6 razy w ciągu roku.This paper is devoted to research on connections between the occurrence of liquid, mixed and solid precipitation forms and air temperature. The analysis was based on meteorological data (daily temperature: average, maximum and minimum, daily precipitation totals and past and current weather notations) covering the period from July 1978 to December 2007. The way of noting meteorological phenomena has not allowed to examine each precipitation case separately. Therefore, days with liquid precipitation (only rain or drizzle occurred during a precipitation day), days with mixed precipitation (only rain and snow or sleet occurred during a precipitation day) and days with solid precipitation (only snow occurred during a precipitation day) were taken into account. In this work the following problems were considered: – average daily temperature on days with various precipitation types, – frequency and conditional probability of various precipitation types occurrence at average daily temperature intervals, – relations between the number of days with various precipitation types (expressed as a percent of days with precipitation) and average monthly air temperature, – relations between variability of the number of days with various precipitation types and air temperature (average, average maximum and minimum) for climatological seasons. It was stated that at Hornsund station the highest frequencies of each of precipitation types were connected with daily temperature slightly higher or lower than 0.0oC (temperature range from 4.0°C to –2.0°C). However, daily temperature range characterized by high conditional probability of solid and liquid precipitation was much wider. While the highest frequencies of liquid precipitation were noted at daily temperature range from 3°C to 4°C, liquid precipitation was also equally probable at higher temperature, reaching 7.0°C. The highest frequencies of solid precipitation occurred at daily temperature intervals from –2.0°C to 0.0°C, however snowfall was also highly probable in the 0.0°C to –11.0°C daily temperature brackets. At Hornsund station liquid precipitation on days with average temperature lower than 0.0oC happened on average 1.1 a year, and they accounted for 0.2% of all days with liquid precipitation. Days with solid precipitation and average temperature above 0.0°C were reported 14.6 times a year and they accounted for 4% of all days with snowfall. At Hornsund station precipitation was not observed on the most frizzing days with average temperature below –26.0°C, when Spitsbergen was under the influence of anticyclone with an inflow of air from NE sector. At Hornsund station connections between average monthly air temperature and contribution of days with liquid precipitation and then days with solid precipitation to the overall number of days with precipitation were the clearest. While the average monthly air temperature was .4.0°C, days with liquid precipitation accounted for 80% to 100% of the overall number of days with precipitation. Days with rain or drizzle were not recorded in months with average temperature below –13.0°C. In months with average temperature .–10.0°C, days with solid precipitation accounts for 80-100% of days with precipitation. It was difficult to determine the critical value of average monthly temperature above which snowfalls did not occur. However, temperature of 5.0°C might be pointed out. Variability of number of days with liquid precipitation was significantly connected with temperature (mostly average maximum one) in autumn. Solid precipitation occurrence significantly depended on summer temperature, especially the average minimum one. However, temperature of nearly each season, except of winter, significantly influenced the number of days with mixed precipitation

The variation of the atmospheric precipitation in Hornsund (Spitsbergen) in the period 1978-2000

In the polar area, the precipitation is a component of one of the most important processes connected with the glacier mass balance ? accumulation and ablation. In this case particular signifi-cance is attributed to the height of the precipitation for a month of a cool season. The aim of this study is to examine the long-term variability of the atmospheric precipitation in Hornsund by the analysis of the monthly, seasonal and annual sums of precipitation and the sums of the precipitation for the accumulation season. Moreover, the long-term variability of the frequency of the days with precipitation (>= 0.0 mm), of the days with trace precipitation (= 0.0 mm), of the days with the precipitation >= 0.1 mm, >= 1.0 mm, >= 5.0 mm, >= 10.0 mm, >= 20.0 mm was discussed in the scale of the year, seasons and the accumulation period. The investigation of long-term variability of the precipitation in Hornsund that was carried out indicated that annual sums of precipitation amount to 421.7 mm. The annual sums of the precipitation are distinguished by the rising tendency showing up from the beginning of the measurement period to 1995. In the second half of the 90-ties, despite of high sums, annual precipitation is characterised by decreasing tendency that is connected with the low sums of precipitation in 1998. The highest part of annual precipitation falls in autumn and slightly less in summer. The lowest precipitation sums appear in spring. A slightly decreasing tendency is visible in the long-term course of spring precipitation. Both the autumn and the summer precipitation is characterised by the higher sums in the last decade of the 20th century than in the earlier period. Moreover, the autumn sums of precipitation are distin-guished by an increasing trend in the last decade of the 20th century while the course of summer precipitation shows the decreasing tendency from 1994. Taking into consideration the monthly values it was stated that September predominates in respect of the height of precipitation. High precipitation also occurs in August. The lowest sums of the monthly precipitation occur in the end of winter and in spring, with especially low sums in May and April. The long-term course of precipitation in particular months is diverse and exhibits specific features. The frequency of the days with defined thresholds of precipitation sums exhibits a great diversity of long-term course in the considered scales of time. The period in the turn of the 80-ties and 90-ties is interesting from the point of view of temporary variability of the frequency of precipitation. In this period the highest frequencies of the days with defined thresholds of precipitation sums often occured or the change of tendencies direction took place

Change in precipitation intensity in Hornsund (Spitsbergen) in the 1878-2008 period

Artykuł porusza problematykę zmian intensywności opadów atmosferycznych w Hornsundzie (Spitsbergen) w okresie 1979-2008. Szczegółową analizę opadów dobowych przeprowadzono w przedziałach/ klasach kwantyli równych sum opadów, które wyznaczono metodą zaproponowaną przez Karla i in. (1995) oraz Karla i Knighta (1998), a zmodyfikowaną przez Osborna i in. (2000), Brunettiego i in. (2001) oraz Brunettiego (2004). Wydzielone klasy kwantyli sum opadów zawierają w sobie łączną informację o sumie i liczbie dni z opadem, dzięki czemu zostały uznane za uproszczony wskaźnik intensywności opadów. Dla każdego z wydzielonych wskaź-ników intensywności, obliczono tendencje udziału opadów w całkowitej sumie rocznej oraz w sumach półroczy i sezonów. W Hornsundzie, w okresie 1979-2008 istotne trendy wzrostowe intensywności opadów zaobserwowano jedynie w okresie rocznym, w półroczu chłodnym oraz jesienią. W pozostałych porach roku oraz w półroczu ciepłym tendencje były nieistotne statystycznie, chociaż na wiosnę zaznaczył się spadek intensywności opadów.This paper deals with problems of temporal changes in distribution of precipitation intensity in Hornsund (Spitsbergen) in the period 1979-2008. Trends in precipitation totals, number of days with precipitation and average daily precipitation amount were calculated in order to assess general changes in precipitation intensity. Detailed analysis of changes in distribution of daily precipitation amount was conducted by categorizing all daily precipitation into 10 classes of precipitation intensity and then computing the proportion of each seasonal total which was provided by events of each class. This class intervals, which can be thought of as 10 equal amount quantiles, were calculated after Osborn et al. (2000). In the next step trends in contribution of each precipitation intensity class-interval to annual and seasonal (warm and cool half-year, spring, summer, autumn, winter) precipi-tation total were calculated. Linear regression fitted by the least square method was used to assess trends magnitude and direction. Trends were expressed in percentage of average indices values for the 1979-2008 period (relative trends) which enabled the comparison of the trends magnitude calcu-lated for indices expressed with different units and for class-intervals characterized by various range of daily precipitation amounts. Statistical significance of trends was checked by Mann-Kendall test. Trends with significance level p between 0.2 and 0.1 were recognized as slightly significant whereas trends with p equal to or less than 0.1 were recognized as significant. The 1979-2008 period was the base for trend analysis. Moreover, several arbitrary selected long-term periods (1979-00, 1979-01, 1979-02, …, 1979-08) were also considered in order to assess the trends stability. In Hornsund in the period 1979-2008 significant changes in daily precipitation intensity appeared on annual basis as well as in cool half year and in autumn. There was a significant increase in annual precipitation total and no sign of any changes in the number of days with precipitation. These were a result of an increase in contribution of extreme precipitation (K10) to total annual precipitation and a decrease in contribution of daily precipitation of low intensity. Similar pattern of precipitation intensity changes was noted in cool half year. In this case the changes are a consequence of decreasing trends in contribution of lower intensity class-intervals (K1, K2 I K4) to total precipitation. In autumn statistically significant were increasing trends in precipitation totals, number of days with precipitation and average daily precipitation amounts – at the same time the increases in precipitation totals and average precipitation amounts were much more higher than in the number of days with precipitation. These changes were a result of decreasing trends in contribution of K1, K2 and K3 intensity classes and increasing trends in contribution of K7 and K8 intensity classes in total autumn precipitation. In spring statistically significant drop in precipitation totals accompanied by unchanged number of days with precipitation indicates the decrease in precipitation intensity. However, detailed analysis of trends in contribution of class-intervals to total winter precipitation has not proven any significant changes of precipitation intensity in this season. It is worth to notice that there were negative trends in contribution of majority of precipitation intensity class-intervals to total spring precipitation which probably resulted in significant decrease in intensity of total precipitation. It also should be mentioned that there are opposite trend directions in spring and autumn precipitation totals. In Hornsund the relationships between precipitation and atmospheric circulation depend on daily precipitation intensity. In majority of seasons daily precipitation of the least intensity (class-interval K1) are the most frequent during an inflow of air masses form east under influence of low pressure system. Precipitation form K4 and higher intensity classes were usually noted in SWc type. It must be said that the results of this study are probably influence by well-known problem of precipitation measu-rement errors in polar regions especially in relation to snow and cool period of year

Circulation conditions favouring fog and low visibility occurrence in Hornsund (Spitsbergen)

W artykule omówiono przebieg roczny występowania mgieł i ograniczonej widzialności poziomej (<1km) w Hornsundzie. Wykorzystano w tym celu dane o zjawiskach meteorologicznych w okresie od lipca 1978 do połowy listopada 2016 roku. Zbiór danych poszerzono o wyniki bardzo dobrej jakości obserwacji zgromadzonych podczas Międzynarodowego Roku Geofizycznego (lipiec 1957 – sierpień 1958). W Hornsundzie mgły występowały średnio podczas 34 dni w roku. Częściej, bo przez 55 dni, widzialność pozioma była ograniczona poniżej 1 km. Zjawiska te najczęściej pojawiały się latem (średnio 21 dni), zwłaszcza w lipcu podczas dni z adwekcją powietrza z południowego zachodu. Dysproporcja pomiędzy częstością występowania dni z mgłą i ograniczoną widzialnością była niewielka latem i osiągała maksimum w zimie kiedy widzialność pozioma jest ograniczona głównie przez intensywne opady śniegu lub zawieje i zamiecie śnieżne. W zimie największym prawdopodobieństwem występowania mgły (8 %) wyróżniała się sytuacja synoptyczna z centrum wyżu nad Spitsbergenem (typ Ca), zaś prawdopodobieństwo wystąpienia ograniczonej widzialności w typach cyklonalnych było większe (18%) niż w typach antycyklonalnych (6%).Data on meteorological phenomenon from Polish Polar Research Station in Hornsund were used to recognize the annual course of fog days and days with horizontal visibility <1km and their relation to atmospheric circulation. Fog occur relatively often in the Arctic being noticed on 34 days a year. Days with limited horizontal visibility are even more frequent (55 days). The highest frequency of the phenomenon falls in summer (21 days), with the clear maximum in July (9 days), mainly on days with south-western air advection. On such days probability of the phenomenon in anticyclonic situation (SWa 56%) is 11% higher than in analogous cyclonic situation (SWc 45%). In summer the frequencies of fog and horizontal visibility <1km are similar. In other season disproportion in the frequency of these phenomena is bigger, particularly in winter. This indicates that in summer the limited visibility is usually due to fog while in other seasons it is related to intense snow precipitation, blowing snow or blizzards. South-western flow of air masses also favours the occurrence of fog and limited horizontal visibility in autumn. In spring these relations are slightly different. The highest probability of the phenomena is related to air advection from the west. Fog occurrence is favoured by Wa type (22%), while limited visibility is related to Wc type(31%). In winter fog probability increases on days with anticyclone centre located over Spitsbergen (Ca 8%). In these season the relation between fog occurrence and atmospheric circulation are quite different than between limited visibility and atmospheric circulation. Limited visibility probability in cyclonic situations (18%) is higher than in anticyclonic (6%), with the maximum in SEc (37%) and Cc (31%) types. In winter visibility is mainly limited by intense snow precipitation, blowing snow and blizzards, which are related to low pressure systems

Dynamics of circulation indices over Spitsbergen

Artykuł dotyczy wieloletnich zmian cyrkulacji atmosfery nad Spitsbergenem opisanej za pomocą trzech syntetycznych wskaźników cyrkulacji – wskaźnika cyrkulacji strefowej W, wskaźnika cyrkulacji południkowej S oraz wskaźnika cykloniczności C – wyznaczonych na podstawie częstości występowania typów cyrkulacji nad Spitsbergenem. W odpracowaniu wykorzystano chronologiczne ciągi wymienionych wskaźników za okres od grudnia 1950 do września 2015 roku. Artykuł jest aktualizacją wcześniejszych opracowań publikowanych w latach 2001 i 2006. Pomimo iż Spitsbergen leży w strefie dominacji wiatrów wschodnich to w okresie badawczym stwierdzono istotny statystycznie wzrost częstości adwekcji powietrza z zachodu oraz wzrost częstości występowania układów niżowych w skali roku. Istotny wzrost występowania sytuacji niżowych stwierdzono również w większości sezonów z wyjątkiem lata. Cyrkulacja strefowa (wskaźnika W) nie podlegała istotnym statystycznie zmianom w rozpatrywanym okresie. Kierunek trendów wskaźnika cyrkulacji południkowej S zmieniał się w zależności od pory roku, przy czym statystycznie istotny był jedynie wzrostowy trend zimą wskazujący na wzrost nasilenia napływu powietrza z sektora południowego.This paper discusses long-term variability of atmospheric circulation over Spitsbergen using three complex circulation indices – zonal circulation index W, meridional circulation index S and cyclonicity index C. The indices were calculated on the basis of the frequency of circulation types occurrence over Spitsbergen. Chronological series of circulation indices covering the period from December 1950 to September 2015 were used. This paper is an update of previously published papers in 2001 and 2006 on the changes in atmospheric circulation over Spitsbergen. Although Spitsbergen is located in the zone of eastern winds dominance, significant increase in the frequency of air advection from the west and increase in the frequency of low pressure systems were found on annual scale. Significant increasing trends in the frequency of cyclonic types were also found in every season except for summer. Trends in W index were not statistically significant on seasonal scale. Direction of trends in meridional circulation index (S index) is diversified depending on season however significant changes were only found in winter indicating an increase in the air advection from the southern sector

The influence of the atmospheric circulation on the occurrence of ice days in Hornsund (Spitsbergen)

Dni mroźne, definiowane jako dni z Tmax<0°C są jednym z termicznych wskaźników współ-czesnych zmian klimatu. Celem artykułu jest określenie wieloletnich zmian częstości występowania dni mroźnych w Hornsundzie oraz określenie relacji pomiędzy ich występowaniem i cyrkulacją atmosfery. Badania przeprowa-dzono na podstawie dostępnych danych dobowej maksymalnej temperatury powietrza (26.07.1957-16.08.1958 MRG; 4.07.1978-29.02.2012). Średnio w Hornsundzie notuje się 183 dni mroźnych w roku. Najczęściej pojawiają się one w marcu, zaś w ogóle nie występują w lipcu i sierpniu. W badanym okresie częstość występowania dni mroźnych istotnie malała w maju, czerwcu i grudniu. Tendencja spadkowa dotyczy również rocznych wartości liczby dni mroźnych. Sezonowe zróżnicowanie relacji pomiędzy częstością występowania dni mroźnych a cyrkulacją atmosfery jest słabsze niż w przypadku dni z przejściem temperatury przez próg 0°C. W większości miesięcy największym prawdopodo-bieństwem ich wystąpienia charakteryzują się typy antycyklonalne: Na, NEa, Ea, NWa oraz Ca i Ka. Występowaniu dni mroźnych nie sprzyja adwekcja ciepłego powietrza z południa.Ice days defined as days with daily maximum temperature below 0°C are placed amongst the indices of current climate change. This paper aims at research both the long-term variability in the ice days occurrence and their relations to atmospheric circulation. All available data on daily maximum temperature were used (26.07.1957-16.08.1958 MRG; 4.07.1978-29.02.2012). On average, 183 ice days a year are noted in Hornsund. The highest number of the days occurs on March whereas they do not appear on July and August. The frequency of ice days were significantly lowering in May, June and August. The downward trend was also found in the annual index values. Seasonal differentiation of the relations between the ice days occurrence and atmospheric circulation are weaker than in case of days with freeze-thaw events. In majority months the highest probability of the ice days occurrence is linked to the six anticyclonic types (Na, NEa, Ea, NWa, Ca and Ka). Advection of warm air from south results in rarer ice days