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

Abstract

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