Abstract
Sunshine duration analysis was based on a series of measurements spanning the period from 1901 to 2014 for Śnieżka (1603 m a.s.l.) and from 1961 to 2000 for Szrenica (1362 m a.s.l.). The average annual sunshine duration (SD) on Śnieżka is 1423.0 h, which is among the lowest values in Poland. On average, the main ridge of the Karkonosze range receives 31% of potential sunshine duration in annual terms: from 25% in December to 36% in August and May. The changes in sunshine duration recorded on Śnieżka point to the existence of two cycles: a short one of approx. 2–4 years and a long one of approx. 60 years. The former most probably reflects the rhythm of atmospheric circulation in the North Atlantic (North Atlantic Oscillation), while the latter reflects the impact of ocean circulation associated with the AMO (Atlantic Multidecadal Oscillation) mechanism. Annual SD totals for the years 1901–2014 exhibit a slight trend to an increase of approx. 2.5 h/10 years, and the rate of increase during the winter quarter is many times higher than during the other seasons. Average monthly sunshine duration differences between Śnieżka and Szrenica are positive for all months of the year with the average monthly difference being 10 to 11 h. This means that the average radiation conditions on Śnieżka are more favourable than the main ridge of the Karkonosze range, which lies at an altitude 200 to 250 m lower. Average daily sunshine durations recorded on Śnieżka are only shorter than those on Szrenica for macro-types of atmospheric circulation with advection from the south.
Highlights
Sunshine duration trends are among the most important issues in studies of climate change, since sunshine duration affects the Earth’s radiation and energy balance
The results presented in the study confirm the slightly downward trends in annual sunshine duration observed in other places, e.g. in Central and South-Eastern Europe (Brázdil et al 1994), in the Czech Republic (Bednar 1990), in Slovakia (Horecka 1990), in Germany (Weber 1990), in Austria (Dobesch 1992), in Spain (Sanchez-Lorenzo et al 2007), in India (Jhajharia and Singh 2011) and in Poland (Morawska-Horawska 1984, 1985; Dubicka 1997; Matuszko 2014)
In the main ridge of the Karkonosze, adverse weather conditions associated with a high degree of cloudiness and lack of sunshine are the result of the presence of orographic clouds, those associated with a föhn (Kwiatkowski and Hołdys 1985)
Summary
Sunshine duration trends are among the most important issues in studies of climate change, since sunshine duration affects the Earth’s radiation and energy balance. Orliczowa (1968) studied the variability of cloud cover and sunshine in the hypsometric profile of the Tatra Mountains. Later Polish publications on sunshine duration in the mountains included work on the variability of sunshine duration in the hypsometric profile of the Western Carpathians (Limanówka and Ustrnul 1993) and its variability in the Sudetes and Carpathian Mountains, including their foreland (Dubicka and Limanówka 1994). Significant studies of the problem of sunshine duration in the Karkonosze Mountains include an article on the Śnieżka climate during the 1961–1990 multi-annual period (Głowicki 1995), the variability of sunshine duration on Śnieżka in connection with atmospheric circulation and cloud cover in the years 1901–1995 (Dubicka 1997) and on Szrenica in the years 1961–1990 (Dubicka and Karal 1994)
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