The purpose of this paper is to compare daily sunshine duration data measured using a Campbell-Stokes sunshine recorder (CS) and a CSD3 sunshine duration sensor (AUTO) as well as to attempt to explain discrepancies between the two data sets. The paper is based on heliographic data and cloudiness observations for [2007][2008][2009][2010][2011][2012]. All the data come from the research station of the Jagiellonian University located in Krakow, Poland. Both instruments tend to produce similar sunshine duration data; however, the electronic sensor tends to show more sunshine duration than the CS. The difference may amount to several hours a day, especially on days with maximum solar radiation. The CSD3 sensor is twice as sensitive as the CS and reacts quickly to solar radiation. This is especially true for the first hour following sunrise, the last hour before sunset and when the Sun's disc becomes visible for short periods of time due to changes in cloudiness. However, there are days when the CSD3 registers less sunshine duration (up to an hour) than the CS. This happens with Cumulus clouds in the sky, which tend to pass the Sun's disc very quickly. The CSD3 sensor does not register sunshine in the presence of thick Altostratus and Cirrostratus clouds due to the relative lack of direct radiation. The sunshine recorder, on the other hand, registers this low level of sunshine.

This paper aims to describe the influence of cloud cover, its extent and cloud genus, on solar radiation intensity measured at the Earth's surface. Solar radiation intensity values at varying degrees of cloudiness, based on observations and measurements performed between 2003 and 2007 in Krakow (Poland), are analysed in this paper. Analyses show that cloud cover impacts solar radiation intensity in two ways: usually weakening it, but intensifying in certain weather conditions. The greatest solar radiation intensity can be detected not when the sky is cloudless, but when it is partly cloudy (3/8-6/8), with convective clouds present.

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ABSTRACT:The article presents characteristics of long-term variability in sunshine duration and total solar radiation in Krakow, reconstructed based on the relative intensity of total radiation (global transmission). The analysis is based on hourly sunshine duration data from the period 1884-2010 and total radiation intensity data from the period -2007 show that the variability of incident solar radiation depends on global factors -circulation-type and anthropogenic-type factors, in particular by industralization between the 1950s and 1980s -which are affected by local conditions.

This paper presents the long-term, annual and diurnal cloud amount values for Cracow (Poland) on the basis of 95-year records. Cloud data were taken from climatological observations made at the Department of Climatology, Jagiellonian University, in the years 1906-2000.On the basis of traditional statistical methods, the following values were calculated: average cloudiness (cloud amount), number of cloudless sky occurrences for three climatological terms, daily and yearly averages, and sums of cloudless days. The cloudiness was also analysed from the point of view of its quality. For that purpose, ten specific genera of clouds adopted in the international classification were examined, taking into account the frequency of their occurrence within every month, separately for each of the climatological periods.