Solar Radiation Change

Abstract

Global solar radiation data were analysed at 10 actinometric stations located in different regions of Poland for the period from 19 (Sosnowiec) to 125 years (Krakow; data partially reconstructed). Only series with the data gaps not exceeding 5% were considered. The most important results of the study of changes in solar radiation in Poland are as follows: (1) the average long-term totals of global solar radiation range in Poland from approximately 3750 MJ/m2 to 4070 MJ/m2 throughout the year; (2) the year-to-year variability of solar radiation expressed by coefficient of variability is rather small and ranges from 3.5 to 7% in Poland; the highest values of variability are observed in autumn and winter; (3) long-term trends of global solar radiation in Poland are in most cases statistically insignificant; a few significant tendencies show different trend directions; (4) relative trends of global solar radiation in the area of Poland do not exceed ±10%/10 years; (5) in Krakow, for a 125-year series of global solar radiation values, about 60 years periodicity of radiation changes can be seen, with three periods of relatively high values (1880–1900, 1940–1960, 1990–2018), separated by periods of relatively low values: 1910–1930 and 1970–1990. The global solar radiation course in Krakow largely corresponds to the periods of “global dimming” and “global brightening” described in different parts of the world as a result of urbanisation, industrialisation and the increase in aerosols related to them. A decrease in values was observed until the end of the 1970s or 1980s, depending on the season of the year, and then there was an increase until the end of the twentieth century.