| Presentation Title: | High-cadence IRIS solar flare imaging and spectroscopy: recent advances and open questions |
| Author(s): | Juraj Lorincik |
Abstract:
High cadence flare campaigns of the Interface Region Imaging Spectrograph (IRIS) opened new windows for studying rapid processes characteristic for flare energy release. Prime example of instrument’s capabilities has been recently set in our imaging and spectroscopic analyses of a confined C4-class flare from 2022 September 25. Using < 2 s cadence imagery from the Slit Jaw Imager, we for the first time revealed flare ribbon kernels exhibiting motions at speeds reaching thousands of kilometers per second. These dynamics are consistent with the slip-running reconnection in quasi-separatrix layers, a phenomenon elusive in observations for nearly two decades. Emission of these kernels was further investigated in our follow-up spectroscopic study focused on the response of the chromospheric and transition region plasma to the energy deposition at sub-second timescales. Intensities of Si IV, C II, and Mg II k lines exhibited enhancements with varying peak times across the ions, with the transition region Si IV enhancements typically preceding those in Mg II by a few seconds. In order to replicate these delays, we investigated a grid of RADYN flare simulations heated by electron beams, thermal conduction, and Alfvén waves. Electron beam parameters were constrained by non-thermal hard X-ray observations of the Gamma-ray Burst Monitor (GBM) of the Fermi spacecraft. Our imaging and spectroscopic studies provide comprehensive insights into the dynamics and energetics of solar flares, validating long-unaddressed theoretical predictions as well as challenging current generation of flare emission models.