Slow and sausage loop mode excitation due to local and global spontaneous perturbations

Abstract

Aims. We analyse the capability of different types of perturbations associated with usual environment energy fluctuations of the solar corona to excite slow and sausage modes in solar flaring loops. Methods. We performed numerical simulations of magnetohydrodynamic ideal equations with a consideration of straight plasma magnetic tubes subject to local and global energy depositions. Results. We find that local loop energy depositions of typical microflares [∼(1027 − 1030) erg] are prone to driving slow shock waves that induce slow-mode patterns. The slow-mode features are obtained for every tested local energy deposition inside the loop. Meanwhile, in order to obtain an observable sausage mode pattern, a global perturbation that is capable of instantaneously modifying the internal loop temperature is required; specifically, the characteristic conductive heating time must be much smaller than the radiative cooling one. Experiments carried out by varying the parameter β demonstrate that the excitation of sausage modes does not significantly depend on the value of this parameter but, rather, depends on the global or local character of the energy source.