Propagation of particles inside a magnetic cloud: Solar Orbiter insights

(Solar Orbiter Nugget #53 by L. Rodríguez-García^1,2, R. Gómez-Herrero², N. Dresing³, L. A. Balmaceda^{4, 5}, E. Palmerio⁶, A. Kouloumvakos⁷, I. C. Jebaraj³, F. Espinosa Lara², M. Roco², C. Palmroos³, A. Warmuth⁸, G. Nicolaou⁹, G. M. Mason⁷, J. Guo¹⁰, T. Laitinen¹¹, I. Cernuda², T. Nieves-Chinchilla⁴, A. Fedeli³, C. O. Lee¹², C. M. S. Cohen¹³, C. J. Owen⁹, G. C. Ho¹⁴ , O. Malandraki¹⁵, R. Vainio³, and J. Rodríguez-Pacheco²)

1. Introduction

Solar energetic particle (SEP) events are sudden bursts of particle intensities linked to solar transient activities [1, 2, 3]. These particles can be released into the solar wind or within interplanetary coronal mass ejections (ICMEs), as a result of impulsive acceleration during flares at the base of the parent ICME or when a newly formed CME-driven shock interacts with one or both legs of existing ICMEs [4, 5, 6, 7, 8]. Moreover, the interplanetary medium through which SEPs travel plays a crucial role in their acceleration and propagation [9]. In this study, we explored the factors that caused the first-arriving particles at Solar Orbiter on January 20, 2022, to be directed toward the Sun during the SEP event.

Figure. 1 Longitudinal spacecraft constellation and magnetic connectivity at 05:58 UT on 20 January 2022 (left) along with multi-spacecraft SEP measurements (right).

2. Context

On January 20, 2022, the Energetic Particle Detector [10, EPD] aboard Solar Orbiter [11] recorded a solar energetic particle (SEP) event, which featured unusually early arriving particles from the anti-Sun direction (Fig. 1). Near-Earth spacecraft, separated by 17° in longitude to the west of Solar Orbiter, detected classic anti-sunward-directed fluxes. Additionally, STEREO-A [12] and MAVEN [13], located 18° to the east and 143° to the west of Solar Orbiter, respectively, also observed the event, indicating that the particles spread over at least 160° in the heliosphere.

Figure 2: Remote and in situ data used in the study. (i) EUV and coronagraph images and GCS [14] 3D reconstruction of the CME (green mesh) and associated driven shock (red mesh) as seen by two different points of view: STEREO/EUVI [15] (b) and SDO/AIA [16] (a); (ii) Fermi-GBM [17] X-ray count rates against the radio spectrogram as observed from STEREO-A/WAVES [18] and Earth (ASSA [19], and YAMAGAWA [20]); (iii) In situ SEP time profiles and plasma and magnetic field observations by Solar Orbiter.

3. Methodology

Using multiple instruments onboard Solar Orbiter and other spacecraft, we analyzed remote-sensing data and radio emissions to identify the parent solar source of the event. As shown in Fig. 2 (i), we observed an eruption, which included an M5.5 flare and a shock driven by a fast coronal mass ejection (CME) traveling at ∼1400 km s⁻¹, ejected from active region (AR) 12929, located near the west limb as seen from Earth. The coronal shock was able to inject particles across a broad range in the corona, reaching the solar wind and interacting with a prior interplanetary CME (ICME) still anchored to the Sun, as discussed below.

We also analyzed SEP parameters, solar wind plasma, and magnetic field data from multiple locations in the heliosphere. As shown in Fig. 2 (iii), at the time of particle injection indicated by the arrow, the spacecraft was embedded within a magnetic cloud (shaded area). We further investigated the anisotropies (which were strong and persistent over time), spectra (which were hard), and composition (which was gradual), all pointing to a time-extended injection likely associated with a coronal shock. The radio spectrogram in Fig. 2 (ii) supports this interpretation, as the presence of TIII bursts starting at 80 MHz and coinciding with the TII bursts suggests that the primary accelerator of the particles is likely the CME-driven shock.
 

Figure 3: Main findings of the investigation. Evolution of AR 12929 from January 16 to 20, 2022: (i, left) Image taken by SDO/AIA on January 16, 2022, at 19:59:11 UT, showing the accumulated pixels of the dimming areas observed during the observation period. (i, right) Image showing the CME-driven shock and the EUV wave on January 20, along with the dimming lobes from the left panel, overlaid in red, positioned as they would have appeared four days later (derotated). (ii) Pitch-angle distribution function of solar wind electrons. (iii) Sketch showing interplanetary configuration of the January 20, 2022, SEP event.

4. Conclusions

Figure 3 summarizes the main findings of the investigation. Panel (i) of Fig. 3 shows the evolution of AR 12929 from January 16 to 20, 2022, illustrating the accumulated pixels of the dimming areas observed during the CME eruption on January 16. We overlaid the position of the dimming lobes in red, as shown in panel (a), which would have rotated over time from January 16 to January 20 (with the image derotated [21] for better visualization). This demonstrates that the eruption on January 20, represented by the CME and CME-driven shock in Fig. 2(i), intersected the dimming lobes of the previous eruption. The pitch-angle distribution function of solar wind electrons, obtained from Solar Orbiter’s SWA-EAS [22], was crucial supporting that, at the time of SEP onset, the western leg of the ICME passing through Solar Orbiter was still connected to the Sun, as evidenced by the observation of only the anti-parallel beam signature.

Figure 3 (iii) also shows the sketch of the proposed scenario: at the time of particle onset, Solar Orbiter was embedded within a magnetic cloud (MC), indicated by the blue shading. This ICME erupted on January 16 from the same AR associated with the SEP event on January 20, whose CME and CME-driven shock are indicated by the red shading and red curve, respectively. Therefore, the main two conclusions of the study are: 

1. The solar source associated with the widespread SEP event on 2022 January 20 is likely the shock driven by the CME eruption observed near the west side from Earth’s perspective. 
2. The energetic particles are injected over a wide angular region into and outside of a previous MC ejected on 2022 January 16 present in the heliosphere at the time of the particle onset on January 20. The sunward propagation particles measured by Solar Orbiter are produced by the injection of particles in the longer (western) leg of the MC, which is still anchored to the Sun. 

This work illustrates how important is the preconditioning of the heliosphere and the interplanetary magnetic field in the transport and spread of SEPs as discussed thrirty years ago by [9].

Further details and references can be found in the study already published in Astronomy & Astrophysics. 

Affiliations

(1) European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain. e-mail: laura.rodriguezgarcia@esa.int
(2) Universidad de Alcalá, Space Research Group (SRG-UAH), Plaza de San Diego s/n, 28801 Alcalá de Henares, Madrid, Spain
(3) Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
(4) Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
(5) Physics and Astronomy Department, George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
(6) Predictive Science Inc., San Diego, CA 92121, USA
(7) The Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, Laurel, MD 20723, USA
(8) Leibniz-Institut für Astrophysik Potsdam (AIP), D-14482 Potsdam, Germany
(9) Mullard Space Science Laboratory, University College London, Dorking RH5 6NT, UK
(10) Deep Space Exploration Laboratory/School of Earth and Space Sciences, University of Science and Technology of China, Hefei
230026, China
(11) Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
(12) Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
(13) California Institute of Technology, Pasadena, CA 91125, USA
(14) Southwest Research Institute, San Antonio, TX 78238, USA
(15) National Observatory of Athens/IAASARS, I. Metaxa & Vas. Pavlou, GR-15236 Penteli, Greece
 

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Acknowledgements

LRG acknowledges support through the European Space Agency (ESA) research fellowship programme. The UAH team acknowledges the financial support by the Spanish Ministerio de Ciencia, Innovación y Universidades FEDER/MCIU/AEI Projects ESP2017-88436-R and PID2019-104863RB-I00/AEI/10.13039/501100011033 and by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 101004159 (SERPENTINE). ND is grateful for support by the Research Council of Finland (SHOCKSEE, grant No.\ 346902). ND, CP, AW, and RV acknowledge funding by the European Union’s Horizon Europe research and innovation program under grant agreement No.\ 101134999 (SOLER). LAB acknowledges the support from the NASA program NNH17ZDA001N-LWS (Awards Nr. 80NSSC19K0069 and 80NSSC19K1235). EP acknowledges support from NASA's LWS (grant no.\ 80NSSC19K0067) and LWS-SC (grant no.\ 80NSSC22K0893) programmes. AK acknowledges financial support from NASA NNN06AA01C (SO-SIS Phase-E) contract. ICJ acknowledges the support of Academy of Finland (SHOCKSEE, grant 346902). AW acknowledges support by the German Space Agency (DLR), grant numbers 50 OT 2304. JG thanks the support from National Natural Science Foundation of China (Grant Nos. 42188101, 42130204, 42474221. TL acknowledges support from the UK Science and Technology Facilities Council (STFC) through grants ST/V000934/1 and ST/Y002725/1. COL acknowledges support from the NASA LWS program (grant no. 80NSSC21K1325) and the MAVEN project funded through the NASA Mars Exploration Program. RV also acknowledges funding by the Research Council of Finland (FORESAIL, grant No. 352847). The authors acknowledge the different SOHO, STEREO instrument teams, and the STEREO and ACE science centers for providing the data used in this paper. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. This research has used PyThea v0.7.3, an open-source and free Python package to reconstruct the 3D structure of CMEs and shock waves (GCS and ellipsoid model). ENLIL simulation results have been provided by the CCMC at NASA Goddard Space Flight Center (GSFC) through their public Runs on Request system (\url{http://ccmc.gsfc.nasa.gov}; run ID Laura\_Rodriguez-Garcia\_121523\_SH\_1). The WSA model was developed by N. Arge, currently at GSFC, and the ENLIL Model was developed by D. Odstrcil, currently at George Mason University.