New insight into transition region dynamics via SUMER observations and numerical modelling

Abstract

We explore the idea that the occurrence of nano-flares in a magnetic loop around the O vi formation temperature could explain the observed red-shift of mid-low transition region lines as well as the blue-shift observed in low coronal lines (T > 6x 10^5\ K). Observations are compared to numerical simulations of the response of the solar atmosphere to an energy perturbation of 4x 10²⁴ ergs representing an energy release during magnetic reconnection in a 1-D semi-circular flux tube. The temporal evolution of the thermodynamic state of the loop is converted into C iv 1548, O vi 1032 and Ne viii 770 line profiles in non-equilibrium ionization. Performing an integration over the entire period of simulations, a redshift of ~ 6\ km\ s^-1 is found in C iv, while a blue-shift of ~ 2\ km\ s^-1 and ~ 10\ km\ s^-1 were derived for O vi and Ne viii, respectively, in reasonable agreement with observations.