This article explains the reasons for the long-term variability in sunshine duration (SD) in Central Europe. It presents a recently discovered mechanism regulating changes in sunshine duration, not described so far in the literature. The periods of global dimming and global brightening were linked with changes in the annual frequency of the macrotypes of the middle-tropospheric circulation and the variability in the surface component of the thermohaline circulation in the North Atlantic (NA THC). On the basis of the totals of annual sunshine duration from the years 1951-2015 from 21 stations located in the Netherlands,

The purpose of this study is to find connections between the North Atlantic Thermohaline Circulation (NA THC), climate elements, such as cloud cover, precipitation, air temperature, sunshine duration, and relative humidity, and flow of rivers in Poland. The intensity of NA THC was characterized by the DG3L index, which was established to assess changes in the amount of heat transported by NA THC along with the transport of water to the Arctic. The paper explains and discusses the mechanism of impact of the NA THC changeability on the elements of the catchment water balance variability. The positive and negative phases of the DG3L index are strongly correlated with the heat anomalies in the upper layer of the North Atlantic waters. The obtained results show that changes of NA THC have significant impact on weather conditions and selected climate elements in Poland. Statistically significant positive correlations were found between the DG3L index and average annual air temperatures, particularly in April, July, and August, while negative between the DG3L index and the total cloud cover. Consequently, in the years with the positive values of the DG3L index, there are favorable conditions for the strong increase in evaporation and evapotranspiration from the ground surface. This has impact on flow of rivers in Poland, which shows considerable regional differences.

Measurements of active‐layer thickness (ALT) at seven locations on Calypsostranda, Svalbard (CALM Site P1), over 1986–2009, are used to estimate the influence of cloudiness, precipitation, air temperature, the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). Between 1986 and 2002, ALT amounted to 118 ± 14 cm and did not show any significant trend. During 2002–06, ALT increased rapidly (12.6 cm yr‐1) to a maximum of ~ 174 cm in 2006 and 2007. In 2008 and 2009, ALT decreased. No statistically significant correlations were determined between ALT and monthly precipitation and cloudiness at Barentsburg, Hornsund and Svalbard Airport stations. There were, however, very strong and highly significant (p < 0.001) relationships with air temperatures in May and June (the strongest association being with Svalbard Airport). The influence of air temperature in May and June on ALT is indirect; it regulates the time of the melt of snow cover, which determines the duration of the ground‐warming period. Using statistical relationships between ALT and air temperature at Svalbard Airport, the time series of ALT at Calypsostranda is reconstructed from 1911 to 2010. It was also found that the AO and the NAO did not significantly affect ALT and air temperature on western Spitsbergen. Copyright © 2013 John Wiley & Sons, Ltd.

Changes in sunshine duration in Poland and their causes (1966–2018) The study discusses changes in the sunshine duration in Poland, occurring in the years 1966–2018. The main analysis was carried out on a series of annual area sunshine duration, calculated from 11 stations, distributed relatively evenly throughout the area of Poland (variable UPLRK). A discontinuity was found in the course of UPLRK, consisting a quantum leap of this value in the years 1987–1989, and then the appearance of a statistically significant positive trend in the course of UPLRK. A change in the course of UPLRK and the total change in the sunshine duration regime occurred at the moment of change in ‘circulation epochs’, characterized by a change in the frequency structure of the mid-tropospheric circulation of macro-types W, E and C according to the Wangengejm-Girs classification. The frequency of these macro-types, by controlling the variability of the lower circulation (SLP fields), controls changes in sunshine duration. An increase in the frequency of the W macro-type, with which the UPLRK values are positively correlated, and a simultaneous decrease in the frequency of the E macro-type, with which sunshine duration is negatively correlated, which occurred at the time of change of macro-circulation epochs in 1987–1989, resulted in corresponding changes in the behavior of the sunshine duration process in Poland. Changes in the frequencies of the W and E macro-types are controlled by changes in the distribution of heat resources in particular waters of the North Atlantic. These changes are controlled by changes in the North Atlantic Thermohaline Circulation (NA THC). As a result, the changes in the UPLRK observed in the years 1966–2018 reconstruct changes in both the macro-circulation conditions in the Atlantic-European circulation sector and changes in the NA THC phases. This allows for a conclusion that the variability of UPLRK is a result of the internal dynamics of the climate system, and not, as it has been believed so far, the effects of anthropogenic changes in the concentration of aerosols in the atmosphere. Zarys treści: W pracy omówiono zmiany usłonecznienia rzeczywistego nad Polską, zachodzące w latach 1966–2018. Zasadniczą analizę przeprowadzono dla szeregu rocznego usłonecznienia obszarowego, obliczonego z 11 stacji względnie równomiernie rozłożonych na obszarze Polski (zmienna UPLRK). Stwierdzono w przebiegu UPLRK wystąpienie nieciągłości, polegającej na skokowym wzroście tej wielkości w latach 1987–1989, a następnie pojawienia się w nim statystycznie istotnego trendu dodatniego. Zmiana przebiegu UPLRK i całkowita zmiana reżimu usłonecznienia nastąpiła w momencie zmiany „epok cyrkulacyjnych”, charakteryzowanych przez zmianę struktury frekwencji makrotypów cyrkulacji środkowotroposferycznej W, E i C według klasyfikacji Wangengejma-Girsa. Frekwencja tych makrotypów, poprzez sterowanie zmiennością cyrkulacji dolnej (polami SLP), steruje zmianami usłonecznienia. Wzrost frekwencji makrotypu W, z którym wartości UPLRK skorelowane są dodatnio, i jednoczesny spadek makrotypu E, z którym usłonecznienie skorelowane jest ujemnie, jaki nastąpił w momencie zmiany epok makrocyrkulacyjnych w latach 1987–1989, pociągnął za sobą odpowiednie zmiany zachowania się przebiegu usłonecznienia nad Polską. Zmiany frekwencji makrotypów W oraz E sterowane są przez zmiany rozkładu zasobów ciepła w poszczególnych akwenach Atlantyku Północnego. Tymi zmianami sterują zmiany cyrkulacji termohalinowej na Atlantyku Północnym (NA THC). W rezultacie obserwowane w latach 1966–2018 zmiany UPLRK odtwarzają zmiany zarówno warunków makrocyrkulacyjnych w atlantycko-europejskim sektorze cyrkulacyjnym, jak i zmiany faz NA THC. Pozwala to na twierdzenie, że zmienność UPLRK stanowi rezultat działania wewnętrznej dynamiki systemu klimatycznego, a nie stanowi, jak do tej pory się uważa, skutków antropogenicznych zmian koncentracji aerozoli w atmosferze.

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