Sequential Chromospheric Brightenings beneath a Transequatorial Halo Coronal Mass Ejection

Abstract

Analyses of multiwavelength data sets for a solar eruption at $21:30 UT on 2002 December 19 show evidence for the disappearance of a large-scale, transequatorial coronal loop ( TL). In addition, coronal manifestations of the eruption ( based on SOHO EIT and LASCO images) include large-scale coronal dimming, flares in each associated active region in the northern and southern hemispheres, and a halo CME. We present detailed observations of the chromospheric aspects of this event based on H images obtained with the ISOON telescope. The ISOON images reveal distant flare precursor brightenings, sympathetic flares, and, of most interest herein, four nearly cospatial propagating chromospheric brightenings. The speeds of the propagating disturbances causing these brightenings are 600-800 km s À1 . The inferred propagating disturbances have some of the characteristics of H and EIT flare waves (e.g., speed, apparent emanation from the flare site, subsequent filament activation). However, they differ from typical H chromospheric flare waves (also known as Moreton waves) because of their absence in off-band H images, small angular arc of propagation (<30 ), and their multiplicity. Three of the four propagating disturbances consist of a series of sequential chromospheric brightenings of network points that suddenly brighten in the area beneath the TL that disappeared earlier. SOHO MDI magnetograms show that the successively brightened points that define the inferred propagating disturbances were exclusively of one polarity, corresponding to the dominant polarity of the affected region. We speculate that the sequential chromospheric brightenings represent footpoints of field lines that extend into the corona, where they are energized in sequence by magnetic reconnection as coronal fields tear away from the chromosphere during the eruption of the transequatorial CME. We report briefly on three other events with similar narrow propagating disturbances that were confined to a single hemisphere.

On the Origin of the Solar Moreton Wave of 2006 December 6

“…Analogous behavior in which eruptions involve structures located outside of strong/complex fields and their associated flares occurs for CMEs originating in transequatorial loops. Such events have been reported by Khan & Hudson (2002) and Balasubramaniam et al (2005).…”

Observation of a Moreton Wave and Wave-Filament Interactions Associated With the Renowned X9 Flare on 1990 May 24

“…From 20:48:28 to 20:48:58 UT, sequential chromospheric brightenings (Balasubramaniam et al 2005) were observed to "propagate" westward within a narrow corridor (Figure 1(a), see also the accompanying animation). These were network points (marked by arrows) that suddenly brightened ahead of the Moreton wavefront (marked by "+" symbols).…”

Are Moreton Waves Coronal Phenomena?

“…1), between 20:41 and 20:43 UT. According to Balasubramaniam et al (2005), SCBs are progression signatures of a coronal mass ejection (CME) that are visible in the chromosphere, at footpoints of magnetic field lines that extend into the corona.…”

“…In a study of coronal waves related to explosive events, Warmuth et al (2005) mention that this event is accompanied by coronal waves seen in H , SOHO EIT, soft X-rays, and He i measurements, and that the Moreton wave for this event has both northward and southward components. Recently, Liu et al (2006) have reported on the relationship between remote brightenings (also known as sequential chromospheric brightenings [SCBs]; e.g., see Balasubramaniam et al 2005) related to this event and the accompanying CME, flare, and Moreton waves. Therein, Liu et al speculate on the possible magnetic connections between the remote brightenings and the flaring region.…”