Wave-like Formation of Hot Loop Arcades

TL;DR

This study observes wave-like formation of hot loop arcades in the solar corona, revealing a consistent pattern of brightening and heating driven by MHD waves and current sheet instabilities, without magnetic structural changes.

Contribution

It provides new observational evidence of wave-like formation of hot arcades and links their heating to MHD wave-induced instabilities in the solar corona.

Findings

Arcades form with wave-like brightening patterns

Wave speed estimated at approximately 700 km/s

Arcades are heated by MHD wave-induced instabilities

Abstract

We present observations of hot arcades made with the Mg XII spectroheliograph onboard the CORONAS-F mission, which provides monochromatic images of hot plasma in the Mg XII 8.42 A resonance line. The arcades were observed to form above the polarity inversion line between Active Regions NOAA 09847 and 09848 at four successive episodes: at 09:18, 14:13, and 22:28 UT on 28 February 2002, and at 00:40 UT on 1 March 2002. The arcades all evolved in the same way: a) a small flare (precursor) appeared near the edge of the still invisible arcade, b) the arcade brightened in a wave-like manner - closer loops brightened earlier, and c) the arcade intensity gradually decreased in $\approx$ 1 h. The estimated wave speed was $\approx$ 700 km s$^{-1}$, and the distance between the hot loops was $\approx$ 50 Mm. The arcades formed without visible changes in their magnetic structure. The arcades were probably heated up by the instabilities of the current sheet above the arcade, which were caused by an MHD wave excited by the precursor.