Vertical Photospheric Currents: Footprints of Eruptive Flux Ropes in the Corona.

Abstract:

In the solar corona, magnetic field is dominant and the current density vector is nearly aligned with the magnetic field lines for strong and stressed field region. Stressed and highly twisted flux ropes are at the origin of eruptive events such as flares and coronal mass ejections which inject material in the interplanetary medium. The standard three dimensional (3D) flare model predicts the complex evolution of flare loops, flux rope before eruption. There are no possibilities to observe directly flux ropes in the corona. However it start to be possible to detect their footprints in the photosphere.

Recent high resolution and temporal spectro-polarimeters have allowed us to compute the photospheric electric currents and follow their evolution. Characteristics pattern like J-shaped ribbons indicate the presence of flux rope before the flare.

We will present the vertical component of current density obtained with the magnetographs (THEMIS, HMI) and with the UNNOFIT inversion code for a few examples (September 2005, February 15 2011, July 12 2012, Sept 10 2014). The results confirm the predictions of the 3D MHD standard model of eruptive flares and allow to understand the evolution of the photospheric currents.