Angular momentum transport and large-scale velocity field on the Sun

Skokić, Ivica (2014) Angular momentum transport and large-scale velocity field on the Sun. Doctoral thesis, Faculty of Science > Department of Physics.

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Abstract

Aims: The main goal of this thesis is to investigate Reynolds stresses and to verify the hypothesis that they are responsible for the angular momentum transport toward the solar equator, maintaining the observed profile of the solar rotation velocity. Residual rotation velocities and meridional velocities and their correlation is also analyzed, as well as their dependence on time, phase of the solar activity cycle and heliographic latitude. Methods: Positions of sunspot groups from GPR (Greenwich Photoheliographic Results) and SOON/USAF/NOAA (Solar Observing Optical Network/United States Air Force/National Oceanic and Atmospheric Administration) catalogs and positions of coronal bright points deduced from images taken by SOHO/EIT (Solar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope) and SDO/AIA (Solar Dynamics Observatory/ Atmospheric Imaging Assembly) were used to calculate velocities, by applying synodic-sidereal and height corrections. Results: Meridional motions of sunspot groups are toward the center of activity, i.e. the mean latitude of sunspot groups, from all observed latitudes and in all phases of the solar activity cycle. Motions of the coronal bright points show a complex pattern variable in time and phase of solar activity. The range of meridional and residual rotation velocities is ±10 m s-1. Expected pattern of torsional oscillations was not observed within statistical significance. Horizontal Reynolds stress is negative at all available latitudes and indicates that there is a minimum value of q _ −3000 m2 s-2 located at latitudes ±30_. Conclusions: In convetion used where positive velocities indicate poleward motions and negative equatorward motions, negative Reynolds stress indicates that angular momentum is trasported toward the solar equator, in agreement with the observed rotational profile of the Sun. Also, an improved method of calculating the synodic-sidereal correction was presented.

Item Type: Thesis (Doctoral thesis)
Keywords: Sun, sunspots, coronal bright points, Reynolds stress, differential rotation, meridional motions, torsional oscillations, solar activity cycle
Supervisor: Brajša, Roman
Date: 27 May 2014
Number of Pages: 105
Subjects: NATURAL SCIENCES > Physics
Divisions: Faculty of Science > Department of Physics
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 11 Jul 2014 11:03
Last Modified: 11 Jul 2014 11:03
URI: http://digre.pmf.unizg.hr/id/eprint/2511

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