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Hinode EIS Observations of Plasma Composition Evolution and Radiative Cooling of Solar Flare Loops

Teodora Mihailescu, Peter R. Young, David H. Brooks, Deborah Baker, Lucie M. Green, David M. Long, Lidia van Driel-Gesztelyi

Abstract

Plasma composition in flaring regions has been shown to have significant spatial and temporal variations, likely driven by dynamical processes that take place as a consequence of the sudden energy release at the reconnection site. The origins of these variations, as well as the effects they might, in turn, have on flare loops dynamics are not yet fully understood. In this work, we investigate the link between flare loop cooling times and plasma composition evolution in the loops formed during the M-class flare peaking at 13:56 UT on the 2022 April 2 using high cadence Hinode EIS spectroscopic observations. The analysis focuses on quantifying the cooling rate (using a series of emission lines covering a wide temperature range) and plasma composition evolution (using the Ca XIV 193.866 A/Ar XIV 194.401 A diagnostic) at the apex and footpoint of the flare loop arcade. Results show slower cooling and a FIP bias of 2.4 +/- 0.2 in the loop footpoint and faster cooling and a stronger FIP bias of 2.8 +/- 0.2 in the loop apex. The potential effects of plasma composition changes on the radiative cooling process of flare loops are also investigated by comparing observed loop cooling times to those predicted by simulations from the EBTEL 0D hydrodynamic model. The EBTEL simulations show that an higher FIP bias would lead to a faster radiative cooling rate and, therefore, shorter cooling times. This suggests that the variation in FIP bias observed in the two features could be responsible for the different cooling times observed.

Hinode EIS Observations of Plasma Composition Evolution and Radiative Cooling of Solar Flare Loops

Abstract

Plasma composition in flaring regions has been shown to have significant spatial and temporal variations, likely driven by dynamical processes that take place as a consequence of the sudden energy release at the reconnection site. The origins of these variations, as well as the effects they might, in turn, have on flare loops dynamics are not yet fully understood. In this work, we investigate the link between flare loop cooling times and plasma composition evolution in the loops formed during the M-class flare peaking at 13:56 UT on the 2022 April 2 using high cadence Hinode EIS spectroscopic observations. The analysis focuses on quantifying the cooling rate (using a series of emission lines covering a wide temperature range) and plasma composition evolution (using the Ca XIV 193.866 A/Ar XIV 194.401 A diagnostic) at the apex and footpoint of the flare loop arcade. Results show slower cooling and a FIP bias of 2.4 +/- 0.2 in the loop footpoint and faster cooling and a stronger FIP bias of 2.8 +/- 0.2 in the loop apex. The potential effects of plasma composition changes on the radiative cooling process of flare loops are also investigated by comparing observed loop cooling times to those predicted by simulations from the EBTEL 0D hydrodynamic model. The EBTEL simulations show that an higher FIP bias would lead to a faster radiative cooling rate and, therefore, shorter cooling times. This suggests that the variation in FIP bias observed in the two features could be responsible for the different cooling times observed.
Paper Structure (3 sections, 1 equation, 3 figures)

This paper contains 3 sections, 1 equation, 3 figures.

Table of Contents

  1. Introduction
  2. Flare Loops Evolution
  3. Hinode EIS Observations

Figures (3)

  • Figure 1: Soft X-ray flux observed in the two GOES channels (1-8 Å and 0.5-4 Å). The vertical dashed lines indicate the start and end times of the Hinode EIS observations, and the yellow rectangle shows the portion of the observations that this study focuses on.
  • Figure 2: Context AIA 94 Å image of the flare loops associated with the M3.9 flare peaking at 13:56 UT on 2022 April 2. The solid white rectangle indicates the position of the EIS slit (for Fe XII 195.119 Å), and the dashed white rectangle shows the loop arcade studied in this work (see Figure \ref{['AIApanel']} for the evolution of this loop arcade). A movie version of this figure, covering the entire duration of the flare from 13:00 to 17:00 UT, is in the online Journal. The image has logarithmic scaling.
  • Figure 3: Close up evolution of the flare loop arcade observed by Hinode EIS, corresponding to the field of view shown in the dashed white rectangle in Figure \ref{['AIAcontext']}. The vertical solid white lines indicate the location of the EIS slit. The horizontal dashed and dotted lines at y=255$^{\prime\prime}$--262$^{\prime\prime}$ and y=233$^{\prime\prime}$--237$^{\prime\prime}$ indicate the regions selected for the loop top and loop footpoint analyses respectively. The image has logarithmic scaling.