Cechy solarne klimatu Łodzi
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The objective of the study was the characterization of solar regime of Łódź and the surroundings e.g. the daily, the annual, the long-term variability of sunshine duration and total and UV solar radiation, the structure of sunshine duration with a special consideration of sunless and very sunny days, the relationship between solar components of climate, the influences of clouds on solar radiation income to an active surfaces, etc. The experimental materials for the study constituted of the daily totals of actual and relative sunshine duration in the period 1951-2000, the daily sums of total solar radiation in the period 1991-2002, measured in the Łódź-Lublinek station (S-W part of the city), 5-year data series of 10-minutes averages of intensity (in Wm-2) of total (305-2800 nm) and UV (290-400 nm) solar radiation in the period 1997-2001, registered in the city center of Łódź. The long-term tendencies of sunshine duration were analyzed by means of linear regression method and sequential version of the non-parametric Mann-Kendall test. All months excluding March, June and September are distinguished by a growing tendency of actual and relative sunshine duration. The number of sunny hours increases in spring, summer and winter, and decreases in autumn. An increase of annual sunshine duration totals (3.5h/year) within the 50-year period was stated. Transformation of the annual course of sunshine duration within 50-year period was detected. The annual maximum of sunshine duration during the first 25-year period occurred in June and September. The second 25-year period was characterized by increase of the number of sunny hour in May and August and by decrease of sunshine duration in June and September. The time of registration of sunshine duration extended in the morning hours and before the Sun set as a consequences of low cloudiness negative trend. The structure of sunshine duration in Łódź was presented in 5 classes of possible sunshine duration (0 - sunless days, 0.1-25% - cloudy days, 25.1-50% - moderately sunny days, 50.1-75% - sunny days, > 75% - very sunny days). Only very sunny days were distinguished by a positive annual totals trend, on average 4 days per 10 years. The tendencies of sunshine duration recorded in Łódź within fifty last years are representative for Poland and result from the macroscale factor (atmospheric circulation) not only from the influences of local (anthropogenic) conditions. The regular fluctuations in the time series of sunshine duration and solar radiation were investigated by Blackman-Tukey classical spectral analysis method. The weak periodicity (statistical insignificance) amounted 8.3, 2.5, 2.8, 3.8 years and the significance short oscillations amounted 182.5, 91.2, 73 days were detected in sunshine duration time series. The total and UV solar radiation time series were characterized by 182.5, 121.7, 73 days significance periodicities. The values of transmission coefficient of total and UV solar radiation were investigated. The daily values of transmission coefficient varied from 25% (total radiation) and 14% (UV) in December to 50% (total radiation) and 26% (UV) in May.