Large-Amplitude Velocity Fluctuations in Coronal Loops: Flare Drivers?

Recent space observations of coronal lines broadening during a flare occurrence suggest that unresolvednonthermal velocity rises well above the background level before the start of the flare, defined as the start ofhard X-ray emission. Using a new shell model to describe the Alfve´nic turbulence inside a coronal loop, it isshown that the occurrence of high values (of the order of 100 km/s) of the large-scale fluctuating velocity canrepresent an efficient trigger to a nonlinear intermittent turbulent cascade and then to the generation of a burstof dissipated energy. The numerical results of the model furnish a well-supported physical explanation for thereason why large velocity fluctuations represent the flare trigger rather than the result of the later energy deposition.

Recent space observations of coronal lines broadening during a flare occurrence suggest that unresolvednonthermal velocity rises well above the background level before the start of the flare, defined as the start ofhard X-ray emission. Using a new shell model to describe the Alfve´nic turbulence inside a coronal loop, it isshown that the occurrence of high values (of the order of 100 km s1) of the large-scale fluctuating velocity canrepresent an efficient trigger to a nonlinear intermittent turbulent cascade and then to the generation of a burstof dissipated energy. The numerical results of the model furnish a well-supported physical explanation for thereason why large velocity fluctuations represent the flare trigger rather than the result of the later energy deposition.