Comprehensive Characterization of Solar Eruptions with Remote and In-Situ Observations, and Modeling: The Major Solar Events on 4 November 2015

Abstract

Solar energetic particles (SEPs) are an important product of solar activity. They are connected to solar active regions and flares, coronal mass ejections (CMEs), EUV waves, shocks, Type II and III radio emissions, and Xray bursts. These phenomena are major probes of the partition of energy in solar eruptions, as well as for the organization, dynamics, and relaxation of coronal and interplanetary magnetic fields. Many of these phenomena cause terrestrial space weather, posing multiple hazards for humans and their technology from space to the ground. Since particular flares, shocks, CMEs, and EUV waves produce SEP events but others do not, since propagation effects from the low corona to 1 AU appear important for some events but not others, and since Type II and III radio emissions and X-ray bursts are sometimes produced by energetic particles leaving these acceleration sites, it is necessary to study the whole system with a multi-frequency and multi-instrument perspective that combines both in-situ and remote observations with detailed modelling of phenomena. This article demonstrates this comprehensive approach, and shows its necessity, by analysing a trio of unusual and striking solar eruptions, radio and X-ray bursts, and SEP events that occurred on 4 November 2015. These events show both strong similarities and differences from standard events and each other, despite having very similar interplanetary conditions and only two flare sites and CME genesis regions. They are therefore major targets for further in-depth observational studies, and for testing both existing and new theories and models. We present the complete suite of relevant observations, complement them with initial modelling results for the SEPs and interplanetary magnetic connectivity, and develop a plausible scenario for the eruptions. Perhaps controversially, the SEPs appear to be reasonably modelled and evidence points to significant non-Parker magnetic fields. Based on the very limited modelling available we identify the aspects that are and are not understood, and we discuss ideas that may lead to improved understanding of the SEP, radio, and space-weather events.

Quasi-Periodic Particle Acceleration in a Solar Flare

“…However, from inspecting Figure 13 where the HXR emission is overplotted on the dynamic spectrum, there is quite a clear relation between the radio bursts and the HXR peaks when the entire frequency band is taken into account. Cairns et al (2020) point out that a type II radio burst occurs at the time of this flare and suggest that the associated shock may be responsible for accelerating the electrons that result in the low frequency radio emission. However, considering the arguments above (points 1-4), we conclude that it is more likely that the type III radio bursts are due to pulses of electron beams accelerating along the open magnetic lines close to the QPP source region.…”

“…However, considering the arguments above (points 1-4), we conclude that it is more likely that the type III radio bursts are due to pulses of electron beams accelerating along the open magnetic lines close to the QPP source region. Additionally, the dynamic spectra of the radio emission from kHz to GHz shows traces of type III bursts that extend to high frequencies, above the frequency of the type II burst (see Cairns et al (2020) Figure 15). This suggests that they originate from a region closer to the flare site.…”

Radio Observations of Coronal Mass Ejection Initiation and Development in the Low Solar Corona

“…Decametric to hectometric type II bursts are generally attributed to shocks driven by CMEs in the corona and heliosphere. However, several examples of type II bursts exist with starting frequencies in the decimetric range (Vrsnak et al, 1995;Cho et al, 2013;Cairns et al, 2020), and the origin of such "high-frequency" type II bursts is somewhat debated. They may be from blast waves due to impulsive heating by flares low in the corona (Magdalenić et al, 2012), driven by the shock of eruptive bubbles, or potentially due to strong lateral expansion (associated with EUV waves) during early-phase flux rope eruption (Patsourakos and Vourlidas, 2012;Nitta et al, 2014).…”

“…A similar assertion can be made for the absence of type III radio bursts in some events. For example, Cairns et al (2020) recently showed an interesting study of three events on the same day, only one of which showed significant type III activity. Those events with no type III bursts were from the same active region, and perhaps provided no means of electron beam escape into the heliosphere, which points to the special configuration of the ambient coronal environment in producing such radio bursts.…”

ORFEES – a radio spectrograph for the study of solar radio bursts and space weather applications

“…Figure8displays the dynamic spectrum of a type II burst in the top panel. The event was presented in Section 5.2 ofCairns et al (2020). The emission starts at unusually high frequencies.…”