Abstract
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 2007–2012. 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.
Highlights
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
Automatic sunshine duration sensors have been replacing the Campbell-Stokes sunshine recorder (CS), which has been in service since the late nineteenth century
With thick, layered clouds of higher tiers (Altostratus and Cirrostratus), which cause scattered radiation, the Campbell-Stokes sunshine recorder records sunshine while the CSD3 does not
Summary
In Poland, synoptic stations began measuring sunshine duration with automatic sensors on 1 January 2014. Several national weather services, including Switzerland, Denmark, the Netherlands, UK and Luxembourg, make their reports on sunshine duration measurements available online Most of these studies mention the existence of differences between the values obtained from different types of devices, but they stop short of explaining the possible causes. They only observe that the introduction of automatic sensors has broken the homogeneity of sunshine measurements and warn against the use of post-2000 data in climatological analyses (Pokorný and Vaníček 2007)
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