Connecting Chromospheric Condensation Signatures to Reconnection Driven Heating Rates in an Observed Flare

TL;DR

This study links chromospheric condensation signatures observed in UV spectra to the energy deposition during solar flare reconnection, validating a quantitative relationship through high-resolution observations and hydrodynamic simulations.

Contribution

It tests and confirms a recent model connecting chromospheric condensation signatures to reconnection-driven heating rates using IRIS observations and simulations.

Findings

Synthetic spectra match observed condensation velocities

Condensation reflects a portion of energy release, not total

Condensation timescale does not equal energy input duration

Abstract

Observations of solar flare reconnection at very high spatial and temporal resolution can be made indirectly at the footpoints of reconnected loops into which flare energy is deposited. The response of the lower atmosphere to this energy input includes a downward-propagating shock called chromospheric condensation, which can be observed in the UV and visible. In order to characterize reconnection using high-resolution observations of this response, one must develop a quantitative relationship between the two. Such a relation was recently developed and here we test it on observations of chromospheric condensation in a single footpoint from a flare ribbon of the X1.0 flare on 25 Oct. 2014 (SOL2014-10-25T16:56:36). Measurements taken of Si iv 1402.77 {\AA} emission spectra using the Interface Region Imaging Spectrograph (IRIS) in a single pixel show red-shifted component undergoing characteristic condensation evolution. We apply the technique called the Ultraviolet Footpoint Calorimeter (UFC) to infer energy deposition into the one footpoint. This energy profile, persisting much longer than the observed condensation, is input into a one-dimensional, hydrodynamic simulation to compute the chromospheric response, which contains a very brief condensation episode. From this simulation we synthesize Si iv spectra and compute the time-evolving Doppler velocity. The synthetic velocity evolution is found to compare reasonably well with the IRIS observation, thus corroborating our reconnection-condensation relationship. The exercise reveals that the chromospheric condensation characterizes a particular portion of the reconnection energy release rather than its entirety, and that the time scale of condensation does not necessarily reflect the time scale of energy input.