Spectroscopy and Differential Emission Measure Diagnostics of a Coronal Dimming Associated with a Fast Halo CME

Abstract

We study the coronal dimming caused by the fast halo CME (deprojected speed v = 1250 km s −1 ) associated with the C3.7 two-ribbon flare on 2012 September 27, using Hinode/EIS spectroscopy and SDO/AIA Differential Emission Measure (DEM) analysis. The event reveals bipolar core dimmings encompassed by hook-shaped flare ribbons located at the ends of the flare-related polarity inversion line, and marking the footpoints of the erupting filament. In coronal emission lines of log T [K] = 5.8 − 6.3, distinct double component spectra indicative of the superposition of a stationary and a fast up-flowing plasma component with velocities up to 130 km s −1 are observed at regions, which were mapped by the scanning EIS slit close in time of their impulsive dimming onset. The outflowing plasma component is found to be of the same order and even dominant over the stationary one, with electron densities in the upflowing component of 2 × 10 9 cm −3 at log T [K] = 6.2. The density evolution in core dimming regions derived from SDO/AIA DEM analysis reveals impulsive reductions by 40-50% within 10 min, and remains at these reduced levels for hours. The mass loss rate derived from the EIS spectroscopy in the dimming regions is of the same order than the mass increase rate observed in the associated white light CME (1 × 10 12 g s −1 ), indicative that the CME mass increase in the coronagraphic field-of-view results from plasma flows from below and not from material piled-up ahead of the outward moving and expanding CME front.

Using radio triangulation to understand the origin of two subsequent type II radio bursts

“…4b and 4c show the dependence of the EIT wave amplitude on the distance from the eruptive centre in sectors 2 and 4, respectively. Close to the source region, we observe areas of minimal intensity i.e., coronal dimming (studied in Veronig et al 2019), which results from the density depletion caused by the evacuation of plasma during the CME lift-off (e.g., Hudson et al 1996;Thompson et al 1998;Dissauer et al 2018). The EIT wave front is characterised by a sharp increase of the intensity towards its maximum (wave crest) followed by a decay to the background level.…”

“…The GOES C3.7 flare (23:35-23:47-1:40 UT) was associated with a two-step filament eruption and a full-halo CME first observed in the SOHO/LASCO C2 field of view at 00:00 UT on September 28, 2012 (Fig. 1a and 1c, respectively; studied in Veronig et al 2019). We also observed on-disk signatures of the CME in the form of a coronal dimming and an EIT wave.…”

EUV imaging and spectroscopy for improved space weather forecasting

“…These transient reductions in intensity represent a significant low-corona signature of a CME (Sterling & Hudson, 1997) and when observed on-disk are an indicator of an Earth-directed CME eruption (Thompson et al, 2000). A careful analysis of the dimming regions can provide early determination of critical energy transfer properties, such as the mass and peak velocity of the departing CME (Robbrecht & Wang, 2010;Dissauer et al, 2018Dissauer et al, , 2019Veronig et al, 2019).…”

Remote coronal dimmings related to a circular-ribbon flare

“…The percentage of density depletion could reach up to 50%−70% (Vanninathan et al 2018). Persistent upflows at speeds of hundreds of km s −1 have been observed using the spectroscopic observations (Harra & Sterling 2001;Harra et al 2007;Attrill et al 2010;Dolla & Zhukov 2011;Tian et al 2012;Veronig et al 2019). The Doppler velocities depend on the formation temperatures of ions (Jin et al 2009), and the most significant dimmings can be observed at temperatures of a few MK (Zhukov & Auchère 2004;Robbrecht & Wang 2010).…”