Abstract
Abstract We performed a differential emission measure (DEM) analysis of candle-flame-shaped flares observed with the Atmospheric Imaging Assembly onboard the Solar Dynamic Observatory. The DEM profile of flaring plasmas generally exhibits a double peak distribution in temperature, with a cold component around $\log T\approx6.2$ log T ≈ 6.2 and a hot component around $\log T\approx7.0$ log T ≈ 7.0 . Attributing the cold component mainly to the coronal background, we propose a mean temperature weighted by the hot DEM component as a better representation of flaring plasma than the conventionally defined mean temperature, which is weighted by the whole DEM profile. Based on this corrected mean temperature, the majority of the flares studied, including a confined flare with a double candle-flame shape sharing the same cusp-shaped structure, resemble the famous Tsuneta flare in temperature distribution, i.e., the cusp-shaped structure has systematically higher temperatures than the rounded flare arcade underneath. However, the M7.7 flare on 19 July 2012 poses a very intriguing violation of this paradigm: the temperature decreases with altitude from the tip of the cusp toward the top of the arcade; the hottest region is slightly above the X-ray loop-top source that is co-spatial with the emission-measure-enhanced region at the top of the arcade. This signifies that a different heating mechanism from the slow-mode shocks attached to the reconnection site operates in the cusp region during the flare decay phase.
Highlights
The sudden, explosive release of magnetic free energy in the solar atmosphere often manifests as three closely related phenomena, namely, flares, prominence/filament eruptions, and coronal mass ejections (CMEs)
We investigate the candle-flame-shaped flares observed in EUV by the Atmospheric Imaging Assembly (AIA: Lemen et al, 2012) onboard the Solar Dynamic Observatory (SDO: Pesnell, Thompson, and Chamberlin, 2012)
The differential emission measure (DEM) analysis on candle-flame-shaped flares reveals that the DEM profile of the flaring plasma generally has a double-peak distribution in temperature, with a cold component around log T ≈ 6.2 and a hot component around log T ≈ 7.0
Summary
The sudden, explosive release of magnetic free energy in the solar atmosphere often manifests as three closely related phenomena, namely, flares, prominence/filament eruptions, and coronal mass ejections (CMEs). As one of the most important discoveries of the Yohkoh mission (Ogawara et al, 1991) that helped shape the modern vision of solar flares, candleflame-shaped flares (Tsuneta et al, 1992) serve as important evidence for magnetic reconnection and have received much attention (e.g., Tsuneta, 1996; Forbes and Acton, 1996; Reeves, Seaton, and Forbes, 2008; Guidoni et al, 2015) In one such flare (21 February 1992, known as the “Tsuneta flare”), it was found that the outer flare loops have systematically higher temperatures in excess of 10 MK, forming a sharp, cusp-shaped structure above the cooler, round-shaped flare arcade (Tsuneta, 1996). In the sections that follow, we briefly introduce the differential emission measure (DEM) method (Section 2), analyze six candle-flame-shaped flares with this method (Section 3), and summarize the results (Section 4)
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