Meridional Motions and Reynolds Stress Determined by Using Kanzelhöhe Drawings and White Light Solar Images from 1964 to 2016
Sunspot position data obtained from Kanzelhöhe Observatory for Solar and Environmental Research (KSO) sunspot drawings and white light images in the period 1964 to 2016 were used to calculate the rotational and meridional velocities of the solar plasma. Velocities were calculated from daily shifts of sunspot groups and an iterative process of calculation of the differential rotation profiles was used to discard outliers. We found a differential rotation profile and meridional motions in agreement with previous studies using sunspots as tracers and conclude that the quality of the KSO data is appropriate for analysis of solar velocity patterns. By analyzing the correlation and covariance of meridional velocities and rotation rate residuals we found that the angular momentum is transported towards the solar equator. The magnitude and latitudinal dependence of the horizontal component of the Reynolds stress tensor calculated is sufficient to maintain the observed solar differential rotation profile. Therefore, our results confirm that the Reynolds stress is the dominant mechanism responsible for transport of angular momentum towards the solar equator.
KeywordsSunspots Differential rotation Velocity fields
This work was partly supported by the Croatian Science Foundation under the project 6212 “Solar and Stellar Variability” and in part by the University of Rijeka under project number 188.8.131.52.03. We wish to express our gratitude to an anonymous referee, whose careful review and detailed criticism of the manuscript helped to improve the presentation and sharpen the arguments.
Disclosure of Potential Conflicts of Interest
The authors declare that they have no conflicts of interest.
- Hržina, D., Roša, D., Hanslmeier, A., Ruždjak, V., Brajša, R.: 2007, Sungrabber – Software for measurements on solar synoptic images. Central European Astrophysical Bulletin 31. ADS.
- Poljančić Beljan, I., Jurdana-Šepić, R., Brajša, R., Sudar, D., Ruždjak, D., Hržina, D., Pötzi, W., Hanslmeier, A., Veronig, A., Skokić, I., Wöhl, H.: 2017, Solar differential rotation in the period 1964-2016 determined by the Kanzelhöhe data set. Astron. Astrophys. 606, A72. DOI. ADS. ADSCrossRefGoogle Scholar
- Veronig, A.M., Pötzi, W.: 2016, Ground-based observations of the solar sources of space weather. In: Dorotovic, I., Fischer, C.E., Temmer, M. (eds.) Coimbra Solar Physics Meeting: Ground-Based Solar Observations in the Space Instrumentation Era, Astronomical Society of the Pacific Conference Series 504, 247. ADS. Google Scholar