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Characteristics and possible causes of high-density, hot, loop-top ridges in two-ribbon flares

Presentation #125.34 in the session General Topics: Solar — Poster Session.

Published onOct 20, 2022
Characteristics and possible causes of high-density, hot, loop-top ridges in two-ribbon flares

Several two-ribbon solar flares, notably including the Bastille flare of 2000-Jul-14, show an extended ridge of plasma running along the looptops of the post-reconnection arcade. Common examples are visible in 193A EUV images due to emission in Fe XXIV at roughly 20 MK. The high, steadily increasing emission measure suggests the ridge is composed of an expanding column of extremely dense plasma. Several past investigations have proposed that these structures result from the collision of evaporation flows from opposing footpoints. We use observations of several such events to characterize the ridge plasma and compare the evaporation-collision hypothesis to an alternative: slow magnetosonic shocks (SMS) in the reconnection outflow. We use a thin flux tube model of the flux retracting following its reconnection to assess the viability of the SMS hypothesis.

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