2019 International Women’s Day event

Abstract

Context. We present a detailed analysis of an eruptive event that occurred on 2019 March 8 in the active region AR 12734, which we refer as the International Women's Day event. The event under study is intriguing based on several aspects: 1) low-coronal eruptive signatures come in "pairs,' namely, there is a double-peaked flare, two coronal dimmings, and two extreme ultraviolet (EUV) waves; 2) although the event is characterized by a complete chain of eruptive signatures, the corresponding coronagraphic signatures are weak; and 3) although the source region of the eruption is located close to the center of the solar disc and the eruption is thus presumably Earth-directed, heliospheric signatures are very weak with very weak Earth impact. Aims. In order to understand the initiation and evolution of this particular event, we performed a comprehensive analysis using a combined observational-modeling approach. Methods. We analyzed a number of multi-spacecraft and multi-instrument (both remote-sensing and in situ) observations, including soft X-ray, EUV, radio and white-light emission, as well as plasma, magnetic field, and particle measurements. We employed 3D nonlinear force-free (NLFF) modeling to investigate the coronal magnetic field configuration in and around the active region, the graduated cylindrical shell (GCS) model to make a 3D reconstruction of the CME geometry, and the 3D magnetohydrodynamical (MHD) numerical model EUropean Heliospheric FORecasting Information Asset (EUHFORIA) to model the background state of the heliosphere. Results. Our results reveal a two-stage C1.3 flare, associated with two EUV waves that occur in close succession and two-stage coronal dimmings that evolve co-temporally with the flare and type II and III radio bursts. Despite its small GOES class, a clear drop in magnetic free energy and helicity is observed during the flare. White light observations do not unambiguously indicate two separate CMEs, but rather a single entity most likely composed of two sheared and twisted structures corresponding to the two eruptions observed in the low corona. The corresponding interplanetary signatures are that of a small flux rope (SFR) with indications of strong interactions with the ambient plasma, which result in a negligible geomagnetic impact. Conclusions. Our results indicate two subsequent eruptions of two systems of sheared and twisted magnetic fields, which already begin to merge in the upper corona and start to evolve further out as a single entity. The large-scale magnetic field significantly influences both the early and the interplanetary evolution of the structure. During the first eruption, the stability of the overlying field was disrupted, enabling the second eruption. We find that during the propagation in the interplanetary space the large-scale magnetic field, that is, the location of heliospheric current sheet (HCS) between the AR and the Earth, is likely to influence propagation, along with the evolution of the erupted structure(s).

The Deformation of an Erupting Magnetic Flux Rope in a Confined Solar Flare

“…In some cases with M-and X-class flares (Hao et al 2012;Chen et al 2017;Gou et al 2017;Ning et al 2019;Zou et al 2019;Zheng et al 2021), the SXR flux only exhibited a short bump or nothing in the impulsive rising phase that lasted for a few minutes. The impulsive phase of the double-peaked flare in this Letter had a period of ∼24 minutes in GOES SXR and ∼34 minutes in AIA 94 Å (yellow and cyan shades in Figure 5(b)), which is similar to that in Dumbović et al (2021). Hence, we suggest that, for the flare involving with two-step magnetic reconnection, the longer the duration of the impulsive phase is, the clearer the profile of the double peaks becomes.…”

Changes of Magnetic Energy and Helicity in Solar Active Regions from Major Flares

“…In particular, the helicity of the current-carrying field and free energy appear to be essentially replenished on this timescale. For smaller flares, the replenishment might happen on shorter timescales, see, e.g., Dumbović et al (2021), Thalmann et al (2022a.…”

Coronal Diagnostics of Solar Type-III Radio Bursts Using LOFAR and PSP Observations

“…The presence of type III radio sources at relatively high distances in the corona, with plasma density higher than expected from the MAS model, suggests that there may be missing information in the modeling. One possibility is the existence of a stealth CME that pushed the coronal magnetic field outward, causing the plasma to appear denser than expected (see Dumbović et al (2021)) -or other non-obvious changes in large-scale coronal magnetic topology. These findings demonstrate that scattering and propagation effects play a significant role in determining the location and directionality of solar radio bursts (Kontar et al 2019(Kontar et al , 2023Chen et al 2023).…”