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

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 2014 October 25 (SOL2014-10-25T16:56:36). Measurements taken of Si iv 1402.77 angstrom emission spectra using the Interface Region Imaging Spectrograph (IRIS) in a single pixel show the redshifted component undergoing characteristic condensation evolution. We apply the technique called the Ultraviolet Footpoint Calorimeter to infer energy deposition into 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 timescale of condensation does not necessarily reflect the timescale of energy input.

Automated summary

Observations of chromospheric condensation can indirectly characterize solar flare reconnection, but only represent a portion of the reconnection energy release and do not necessarily reflect the timescale of energy input. Developing a quantitative relationship between high-resolution observations of condensation response and reconnection dynamics is crucial for understanding the complex processes involved in solar flares.