Neural network prediction of solar cycle 24

The ability to predict the future behavior of solar activity has become extremely import due to its effect on the environment near the Earth. Predictions of both the amplitude and timing of the next solar cycle will assist in estimating the various consequences of space weather. The level of solar activity is usually expressed by in- ternational sunspot number （Rz）. Several prediction techniques have been applied and have achieved varying degrees of success in the domain of solar activity prediction. We predict a solar index （Rz） in solar cycle 24 by using a neural network method. The neural network technique is used to analyze the time series of solar activity. According to our predictions of yearly sunspot number, the maximum of cycle 24 will occur in the year 2013 and will have an annual mean sunspot number of 65. Finally, we discuss our results in order to compare them with other suggested predictions.

Numerical simulation of the Hall effect in magnetized accretion disks with the Pluto code

We investigate the Hall effect in a standard magnetized accretion disk which is accompanied by dissipation due to viscosity and magnetic resistivity. By consider- ing an initial magnetic field, using the PLUTO code, we perform a numerical magne- tohydrodynamic simulation in order to study the effect of Hall diffusion on the physi- cal structure of the disk. Current density and temperature of the disk are significantly modified by Hall diffusion, but the global structure of the disk is not substantially affected. The changes in the current densities and temperature of the disk lead to a modification in the disk luminosity and radiation.

Structure of ADAFs in a general large-scale B-field:the role of wind and thermal conduction

We have explored the structure of a hot flow bathed in a general large-scale magnetic field. The importance of outflow and thermal conduction on the self-similar structure of a hot accretion flow has been investigated. We consider the additional 2 2 2 magnetic parameters are the Alfv6n sound speeds in three directions of cylindrical coordinates. In comparison to the accretion disk without winds, our results show that the radial and rotational velocities of the disk become faster, but the disk becomes cooler because of the angular momentum and energy flux which are taken away by the winds. Moreover, thermal conduction opposes the effect of winds and not only decreases the rotational velocity but also in- creases the radial velocity as well as the sound speed of the disk. In addition, we study the effect of the global magnetic field on the structure of the disk. Our numerical re- suits show that all the components of a magnetic field can be important and they have a considerable effect on velocities and vertical structure of the disk.

Hydrodynamical wind in magnetized accretion flows with convection

The existence of outflow and magnetic fields in the inner region of hot accretion flows has been confirmed by observations and numerical magnetohydrodynamic（MHD）simulations.We present self-similar solutions for radiatively inefficient accretion flows（RIAFs）around black holes in the presence of outflow and a global magnetic field.The influence of outflow is taken into account by adopting a radius that depends on mass accretion rateM=M0 （r/r0）s with s〉0. We also consider convection through a mixing length formula to calculate convection parameterαcon.Moreover we consider the additional magnetic field parameters βr,φ,z=c2 r,φ,z /（2c2 s ）,where c2 r,φ,z are the Alfvén sound speeds in three directions of cylindrical coordinates.Our numerical results show that by increasing all components of the magnetic field,the surface density and rotational velocity increase,but the sound speed and radial infall velocity of the disk decrease.We have also found that the existence of wind will lead to reduction of surface density as well as rotational velocity.Moreover,the radial velocity,sound speed,advection parameter and the vertical thickness of the disk will increase when outflow becomes important in the RIAF.