engleski

A comparison of sunspot position measurements from different data sets

There are several data sets containing information about the positions of sunspots and sunspot groups that differ in format and precision, e.g. GPR (Greenwich Photoheliographic Results) and SOON/USAF/NOAA (Solar Optical Observing Network/United States Air Force/National Oceanic and Atmosferic Administration). The aim of this paper is to check the precision of the SOON/USAF/NOAA data set and compare it with the GPR data set. For this purpose, we have used a third data set, the Kanzelhöhe Observatory data set, as a basis of sunspot position measurments comparison. The positions of selected sunspot groups in the digitized Solar Observatory Kanzelhöhe drawings were determined with a special software Sungrabber. The selected groups consisted mostly of single sunspots (Zürich types H and J) from the years 1972 and 1993 belonging to the similar phases of the solar activity cycles. The determined Kanzelhöhe sunspot group coordinates were compared with those from GPR for the year 1972 and SOON/USAF/NOAA for the year 1993. The rotation velocities calculated for sunspot groups observed at Kanzelhöhe were compared with the ones obtained from the two data sets mentioned above in the same observing periods. With the assumption of constant precision of Kanzelhöhe drawings, it was established that SOON/USAF/NOAA data are somewhat less precise than the GPR ones.

heliographic coordinates; heliographic longitude; heliographic latitude; angular velocity; data set

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