Solar differential rotation in the period 1964–2016 determined by the Kanzelhöhe data set

Abstract

Context. Kanzelhöhe Observatory for Solar and Environmental Research (KSO) provides daily multispectral synoptic observations of the Sun using several telescopes. In this work we made use of sunspot drawings and full disk white light CCD images. Aims. The main aim of this work is to determine the solar differential rotation by tracing sunspot groups during the period 1964 -2016, using the KSO sunspot drawings and white light images. We also compare the differential rotation parameters derived in this paper from the KSO with those collected fromf other data sets and present an investigation of the north -south rotational asymmetry. Methods. Two procedures for the determination of the heliographic positions were applied: an interactive procedure on the KSO sunspot drawings (1964 -2008, solar cycles nos. 20 -23) and an automatic procedure on the KSO white light images (2009 -2016, solar cycle no. 24). For the determination of the synodic angular rotation velocities two different methods have been used: a daily shift (DS) method and a robust linear least-squares fit (rLSQ) method. Afterwards, the rotation velocities had to be converted from synodic to sidereal, which were then used in the least-squares fitting for the solar differential rotation law. A comparison of the interactive and automatic procedures was performed for the year 2014. Results. The interactive procedure of position determination is fairly accurate but time consuming. In the case of the much faster automatic procedure for position determination, we found the rLSQ method for calculating rotational velocities to be more reliable than the DS method. For the test data from 2014, the rLSQ method gives a relative standard error for the differential rotation parameter B that is three times smaller than the corresponding relative standard error derived for the DS method. The best fit solar differential rotation profile for the whole time period is ω(b) = (14.47 ± 0.01) -(2.66 ± 0.10) sin 2 b (deg/day) for the DS method and ω(b) = (14.50 ± 0.01) -(2.87 ± 0.12) sin 2 b (deg/day) for the rLSQ method. A barely noticeable north -south asymmetry is observed for the whole time period 1964 -2016 in the present paper. Rotation profiles, using different data sets, presented by other authors for the same time periods and the same tracer types, are in good agreement with our results. Conclusions. The KSO data set used in this paper is in good agreement with the Debrecen Photoheliographic Data and Greenwich Photoheliographic Results and is suitable for the investigation of the long-term variabilities in the solar rotation profile. Also, the quality of the KSO sunspot drawings has gradually increased during the last 50 years.

Meridional Motions and Reynolds Stress Determined by Using Kanzelhöhe Drawings and White Light Solar Images from 1964 to 2016

“…The differential rotation profile obtained in this work is the same (within 1σ) as the one obtained by Poljančić Beljan et al (2017) (2017). The values of differential rotation parameters from different methods and datasets are compared in more detail in Sudar et al (2015) and Poljančić Beljan et al (2017).…”

“…Since the Solar Cycle 23 ended in 2008 to have an homogeneous dataset within the solar cycle only the data during 2009-2016 were obtained by the automatic method. A detailed description of both methods and the availability of the data is given in Poljančić Beljan et al (2017).…”

“…Consequently, the venture of determination of the heliographic positions from the sunspot drawings and full disc white light CCD images was undertaken. The procedure and results for solar rotation in the period 1964-2016 are presented in Poljančić Beljan et al (2017). Here we present the analysis of meridional motions and Reynolds stress determined from KSO data in the same period 1964-2016.…”

Kanzelhöhe Observatory: Instruments, Data Processing and Data Products

“…White light images and sunspot drawings are used for deriving solar differential rotation rates and meridional flows (e.g. Hanslmeier and Lustig, 1986;Lustig and Hanslmeier, 1987;Poljančić Beljan et al, 2017;Ruždjak et al, 2018), as well as for sunspot catalogs (Baranyi, Győri, and Ludmány, 2016). Ca II K images are used for long-term solar irradiance investigations (e.g.…”

Observing the changing surface structures of the active K giant σ Geminorum with SONG

“…In the solar case, tracking the movement of sunspots has been used to study solar differential rotation, for example by Balthasar et al (1986) and Poljančić Beljan et al (2017). Doing the same in the stellar case is more challenging due to a lack of spatial and temporal resolution in the available observations (for different stellar techniques see, e.g.…”