Observational Signatures of Electron-driven Chromospheric Evaporation in a White-light Flare

Abstract

We investigate observational signatures of explosive chromospheric evaporation during a white-light flare (WLF) that occurred on 2022 August 27. Using the moment analysis, bisector techniques, and the Gaussian fitting method, redshifted velocities of less than 20 km s−1 are detected in low-temperature spectral lines of Hα, C i, and Si iv at the conjugated flare kernels, which could be regarded as downflows caused by chromospheric condensation. Blueshifted velocities of ∼30−40 km s−1 are found in the high-temperature line of Fe xxi, which can be interpreted as upflows driven by chromospheric evaporation. A nonthermal hard X-ray (HXR) source is cospatial with one of the flare kernels, and the Doppler velocities are temporally correlated with the HXR fluxes. The nonthermal energy flux is estimated to be at least (1.3 ± 0.2) × 1010 erg s−1 cm−2. The radiation enhancement at Fe i 6569.2 Å and 6173 Å suggests that the flare is a WLF. Moreover, the while-light emission at Fe i 6569.2 Å is temporally and spatially correlated with the blueshift of the Fe xxi line, suggesting that both the white-light enhancement and the chromospheric evaporation are triggered and driven by nonthermal electrons. All of our observations support the scenario of an electron-driven explosive chromospheric evaporation in the WLF.

Formation of Fan-spine Magnetic Topology through Flux Emergence and Subsequent Jet Production

“…These results indicate the presence of redshifted signatures in the circular ribbon and inner patch (panel (A)) both before and during the first jet eruption. This phenomenon can be attributed to chromosphere condensation (e.g., Tian et al 2015;Li et al 2017Li et al , 2023. However, in Figure 7(B) the redshifted signature is likely caused by the cooling plasma falling back to the solar surface along the dome-shaped fan.…”