Figure 1: Right: Longitudinal spacecraft constellation and magnetic connectivity at 16:00 UT on 17 April 2021. The spiral lines represent electromagnetic field lines linking the spacecraft to the Sun (colored solid) and the flare website to the heliosphere (black rushed). The black arrow marks the longitude of the flare, red and blue arrows show the instructions of various distinct SEP injection episodes as determined from radio bursts analyses. (Figure produced with Solar-MACH (Gieseler et al. 2023)). Left: Multi-spacecraft SEP observations of ∼ 1 MeV electrons (top) and ∼ 25 MeV protons (bottom) observed by the spacecraft suggested by the same colors in the best figure.
Fig. 1 (left) reveals SEP observations by 5 different observer positions in the inner heliosphere, who identify the occasion: Solar Orbiter (SolO), Parker Solar Probe (PSP), STEREO A, SOHO and Wind near Earth, and BepiColombo. Fig. 1 right reveals the corresponding spacecraft constellation.
Fig. 2 reveals radio spectrograms observed by PSP, SolO, STEREO A, and Wind. PSP (top) observes the most complicated radio signal with four distinct type III burst groups (TIII) and 3 type II burst episodes (TII), completely lasting over a duration of 40 minutes. While TIII( 1) and TIII( 3) are observed by all spacecraft, TIII( 2) and TIII( 4) are only seen by PSP, recommending that these propagate into different instructions than the other bursts. This is additional supported by their strong polarization (2nd panel of Fig. 2), which suggests that these propagate towards the PSP spacecraft, shown by the blue arrow in Fig. 1 (right). For TIII( 1) and TIII( 3) we performed a radio proliferation analysis using the multi-spacecraft radio observations. The resulting propagation instructions are marked by the two red arrows in Fig. 1 (right). Completely, a longitudinal series of 110 ° is spanned by the different injection directions, marked by the gray shaded area.
An enduring issue in solar energetic particle (SEP) research studies is to determine their source areas at the Sun. A particular type of SEP events shows really large particle spreads out up to all around the Sun. The systems proposed so far to produce these prevalent events are an extremely wide SEP injection region, likely a shock, or strong perpendicular diffusion in the interplanetary medium (e.g., Dresing et al. 2014). Our exhaustive multi-spacecraft analysis of the 17 April 2021 widespread SEP event revealed a brand-new potential driver for widespread events, that is several distinct SEP injections at the Sun, which head into considerably various directions. The black arrow marks the longitude of the flare, red and blue arrows reveal the instructions of various unique SEP injection episodes as identified from radio bursts analyses.
Figure 2: Radio spectrograms from all readily available space-borne observatories of the 17 April 2021 event. From top to bottom panels 1 and 2 program Stokes I and the net polarization (Stokes V/I) from PSP. Panels 3– 5 show the Stokes I measurements from SolO, STEREO A, and Wind, respectively. The various bursts are shown in panel 1. The type II (TII) bursts are marked in other panels by rectangle-shaped boxes of red, yellow, and orange.
We conclude that unique SEP injections into considerably various longitudinal instructions, which were all related with the exact same solar activity, play a significant role in producing the extensive SEP observations of the 17 April 2021 event. Nevertheless, perpendicular diffusion, and potentially also the shock, likely contributed as well.
Based upon the recent paper by Dresing, N., Rodríguez-García, L., Jebaraj, I. C., Warmuth, A., Wallace, S., Balmaceda, L. et al., The 17 April 2021 extensive solar energetic particle event, A&A, 674, A105: 2023, doi:10.1051/ 0004-6361/2023 45938.
References.
Dresing, N., Gómez-Herrero, R., Heber, B. et al. 2014, A&A, 567, A27.
Gieseler, J., Dresing, N., Palmroos, et al. 2023., FrASS, 9, 384.
A long-standing problem in solar energetic particle (SEP) research studies is to pinpoint their source regions at the Sun. Potential contributions by both the flare and CME-driven shocks make complex the analysis. A specific kind of SEP events shows very broad particle spreads up to all around the Sun. The systems proposed so far to create these extensive occasions are a really broad SEP injection region, likely a shock, or strong perpendicular diffusion in the interplanetary medium (e.g., Dresing et al. 2014). Our exhaustive multi-spacecraft analysis of the 17 April 2021 widespread SEP event exposed a brand-new potential motorist for prevalent events, that is several unique SEP injections at the Sun, which head into significantly different directions. Multi-spacecraft radio observations were type in discovering this new circumstance.
