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Öğe A magnetohydrodynamic model applied to the lower convective region in the Sun(Oxford Univ Press, 2007) Cavus, H.; Karafistan, A. I.We have investigated the effects of a toroidal-type magnetic field of 10 T (10(5) G), in the lower convective region of a standard solar model. From the numerical solution of the magnetohydrodynamic (MHD) equations, distributions of some physical variables are obtained in spherical coordinates for this layer. It is shown that the most important feature of this type of magnetic field is to break the spherical symmetric distribution of density and alter its compressibility with respect to latitude. This type of magnetic field does not change much the density of the reference model, and the resulting flux is also comparable to that found in other research. It is further shown that the MHD plasma acts as incompressible at the poles, in contrast to the perfect fluid behaviour at the equator. As a result we have estimated the limits and applicability of the anelastic and Boussinesq approximations for this layer. Thus our results might be useful, especially in simplifying the numerical integration schemes related to the lower convection zone in the Sun.Öğe Effect of Viscosity on Shock Waves Observed After Two Different Coronal Mass Ejection Activities CME20/11/2003 and CME11/04/2010(Springer/Plenum Publishers, 2017) Cavus, H.; Zeybek, G.Coronal mass ejections are the main results of powerful solar activity. These activities are capable of generating shock waves in the interplanetary medium. The shock waves happen when the solar particles change their velocities from supersonic to subsonic. Since the interaction of shock waves with viscosity is one of the central problems in the supersonic regime of compressible gas flow, investigations of these events play a crucial role in space weather research [1]. The main purpose of this study is to study the effects of viscosity on the shock waves observed after the CMEs of 20/11/2003 and CME11/04/2010.Öğe Effects of viscosity on the behavior of entropy change in the shock wave that occurred after the December 13, 2006 coronal mass ejection(Maik Nauka/Interperiodica/Springer, 2015) Cavus, H.; Kurt, A.Coronal mass ejections (CMEs) and the solar wind are the two main demonstrations of solar activity. These events can drive a shock wave. The shock wave occurs where the solar wind changes from being supersonic (with respect to the surrounding interplanetary medium) to subsonic. The main purpose of this study is to apply the algorithm and the results given in our recent papers to the shock wave that happened after the December 13, 2006 CME, and evaluate the behavior of entropy during this solar activity.Öğe On the effect of magnetic field on the low-l solar p-mode oscillations(Elsevier Science Bv, 2010) Cavus, H.; Karafistan, A. I.One of the possible magnetic field effects on the stellar pulsations is known to be a splitting in the observed frequencies. Using this knowledge in the solar convection zone, there are two aims in this work Considering the Sun as an incompressible fluid, our first objective was to investigate the variation of the physical parameters in the 30% outermost convective solar layer, during a pulsation period. The second purpose was to calculate, by means of the spherical harmonics, the shifts on the low-l p-mode frequencies which could be caused by the presence of the magnetic field in the Sun. The first order perturbation approximation was used in order to calculate analytically the resulting frequency shifts and the small perturbations on the magnetic field, as well as the physical parameters, such as density, pressure and temperature, of a Standard Solar Model excluding both rotation and magnetic field (Christensen-Dalsgaard et al., 1996) in the unperturbed equilibrium case. (C) 2010 Published by Elsevier B.V.Öğe On the Modelling of Rotational Effects in the Lower Convective Region of the Sun(Springer, 2010) Cavus, H.; Karafistan, A. I.The purpose of this work is to study effects of differential rotation in the lower convective region of the Sun. Similar to MHD case; the governing equations are separated in variables, allowing numerical integration in this layer. This algorithm facilitates solutions of more complicated systems, with less computing time. Two different known rotation profiles are used in order to fit the model. The fitting procedure is accomplished by making use of sphericity and density shape parameters related to the rotation profiles. It is also shown that the most important feature of rotation is to break the spherical symmetric distribution of density in this layer. As in the MHD effects found before, differential rotation changes considerably the density of the reference model for both cases.Öğe On the variations of some physical quantities above the sunspot bands near the equatorial plane(Maik Nauka/Interperiodica/Springer, 2016) Cavus, H.; Ilbikci, N.In this work, some solutions of magnetohydrodynamic (MHD) equations are searched in order to investigate some large scale physical quantities in the sunspot dominated latitudinal regions near the equatorial plane. Special separation of variables is used to obtain the radial and latitudinal changes in spherical coordinates. Present parametric analysis yields three important parameters which are the sphericity, density and radial components shape parameters in the latitudinal distributions of physical variables. In the region of interest there is a considerable change in physical quantities with respect to regions where sunspots do not appear.Öğe On the viscosity effects in the shock wave observed in the solar wind after the December 13, 2006 coronal mass ejection(Maik Nauka/Interperiodica/Springer, 2015) Cavus, H.Coronal mass ejections (CMEs) and solar wind are the main results of solar activity. These events can drive interplanetary shock waves and produce geomagnetic storms. The study of these events is very important for space weather purposes. The shock waves occur where the solar wind changes its characteristics from being supersonic (with respect to the surrounding interplanetary medium) to being subsonic. In the supersonic regime of compressible gas flow, the interaction of shock waves with viscosity is one of the central problems. The main purpose of this study is to search for the effects of viscosity in the shock wave observed after the December 13, 2006 coronal mass ejection.Öğe Some MHD solutions for the bottom of the solar convective layer(Astronomical Soc Pacific, 2007) Cavus, H.; Karafistan, A. I.The magnetic field responsible for the solar activity is stored in the base of the convective zone. Applying this knowledge to the bottom of the convection zone in the Sun our objective was to investigate some magnetohydrodynamical (MHD) solutions. The first order perturbation approximation was used in order to calculate the small perturbations on the physical parameters of a Standard Solar Model (SSM) excluding both rotation and magnetic field (Christensen-Dalsgaard et al. 1996) in the unperturbed equilibrium case. The validity of each approximation is tested and examined from the SSM. The MHD results thus obtained are presented graphically and compared with those of the SSM.
