Numerical simulations of solar spicules: Adiabatic and non-adiabatic studies

Abstract

Aims. We aim to study the formation and evolution of solar spicules using numerical simulations of a vertical velocity pulse that is launched from the upper chromosphere. Methods. With the use of the PLUTO code, we numerically solved adiabatic and non-adiabatic magnetohydrodynamic (MHD) equations in 2D cylindrical geometry. We followed the evolution of spicules triggered by pulses that are launched in a vertical velocity component from the upper chromosphere. Then we compared the results obtained with and without non-adiabatic terms in the MHD equations. Results. Our numerical results reveal that the velocity pulse is steepened into a shock that propagates upward into the corona. The chromospheric cold and dense plasma follows the shock and rises into the corona with the mean speed of 20–25 km s-1 . The nonlinear wake behind the pulse in the stratified atmosphere leads to quasi-periodic rebound shocks, which lead to quasi-periodic rising of chromospheric plasma into the corona with a period close to the acoustic cut-off period of the chromosphere. We found that the effect of non-adiabatic terms on spicule evolution is minor; the general properties of spicules such as their heights and rising-time remain slightly affected by these terms. Conclusions. In the framework of the axisymmetric model we devised, we show that the solar spicules can be triggered by the vertical velocity pulses, and thermal conduction and radiative cooling terms do not exert any significant influence on the dynamics of these spicules.