Solar flares and Kelvin-Helmholtz instabilities: A parameter survey

Abstract

Hard X-ray (HXR) sources are frequently observed near the top of solar flare loops, and the emission is widely ascribed to bremsstrahlung. We here revisit an alternative scenario which stresses the importance of inverse Compton processes and the Kelvin- Helmholtz instability (KHI) proposed by Fang et al. (2016). This scenario adds a novel ingredient to the standard flare model, where evaporation flows from flare-impacted chromospheric foot-points interact with each other near the loop top and produce turbulence via KHI. The turbulence can act as a trapping region and as an efficient accelerator to provide energetic electrons, which scatter soft X-ray (SXR) photons to HXR photons via the inverse Compton mechanism. This paper focuses on the trigger of the KHI and the resulting turbulence in this new scenario. We perform a parameter survey to investigate the necessary ingredients to obtain KHI through interaction of chromospheric evaporation flows. When turbulence is produced in the loop apex, an index of -5/3 can be found in the spectra of velocity and magnetic field fluctuations. The KHI development and the generation of turbulence are controlled by the amount of energy deposited in the chromospheric foot-points and the time scale of its energy deposition, but typical values for M class flares show the KHI development routinely. Asymmetry of energy deposition determines the location where the turbulence is produced, and the synthesized SXR light curve shows a clear periodic signal related to the sloshing motion of the vortex pattern created by the KHI.

arXiv comment12 pages, 14 figures

References in corpus (17)

• CHIANTI - An atomic database for Emission Lines. Version 8
• Radiative Hydrodynamic Models of the Optical and Ultraviolet Emission from Solar Flares
• Imaging coronal magnetic-field reconnection in a solar flare
• MPI-AMRVAC for Solar and Astrophysics
• MPI-AMRVAC 2.0 for Solar and Astrophysical Applications
• Velocity Characteristics of Evaporated Plasma Using Hinode/EIS
• RHESSI and SOHO/CDS Observations of Explosive Chromospheric Evaporation
• Temporal evolution of chromospheric evaporation: case studies of the M1.1 flare on 2014 September 6 and X1.6 flare on 2014 September 10
• Imaging and spectroscopic observations of magnetic reconnection and chromospheric evaporation in a solar flare
• Turbulent kinetic energy in the energy balance of a solar flare
• Global sausage oscillation of solar flare loops detected by the Interface Region Imaging Spectrograph
• RHESSI Observation of Chromospheric Evaporation
• Turbulent pitch-angle scattering and diffusive transport of hard-X-ray producing electrons in flaring coronal loops
• Modelling of Reflective Propagating Slow-mode Wave in a Flaring Loop
• Reflection Of Propagating Slow Magneto-acoustic Waves In Hot Coronal Loops : Multi-instrument Observations and Numerical Modelling
• Soft X-ray emission in kink-unstable coronal loops
• The Role of Inverse Compton Scattering in Solar Coronal Hard X-ray and Gamma-ray Sources

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• Scaling laws of quasi-periodic pulsations in solar flares
• Imaging and Spectroscopic Observations of the Dynamic Processes in Limb Solar Flares
• Nonthermal electron acceleration in turbulent post-flare coronal loops
• Accessing the fine temporal scale of EUV brightenings and their quasi-periodic pulsations: 1 second cadence observations by Solar Orbiter/EUI