5:15 PM - 7:15 PM
[PEM16-P03] Source region of the type-II solar radio bursts in the HF frequency range associated with a CME on 13 June 2022
Keywords:Solar Radio Burst, Coronal Mass Ejections (CMEs), Solar physics
Coronal Mass Ejections (CMEs) are large plasma masses ejected into interplanetary space due to active solar activities. The propagation of MHD shock waves produced by CMEs generates type II solar radio burst (SRB II) through various plasma elementary processes [e.g. Uchida, 1960]. Analyzing the frequency temporal evolution of SRB II, we can estimate the speed of the CME shock wave as well as the density structure and magnetic field strength of the solar corona [e.g., Kong et al., 2012; Feng et al., 2012, 2013; Koval et al., 2021, 2023, 2024]. CMEs have a significant impact on the space environment around the Earth when they reach Earth. By using the frequency–time evolution of SRB II, which propagates at the speed of light, we can predict the speed and position of the CMEs as well as the magnetic field structure near the CME source before they reach Earth. This approach improves CME arrival predictions like solar wind/CME propagation MHD simulations (e.g., SUSANOO-CME; Shiota and Kataoka, 2016) and it will be the key to dealing with space disasters. However, because the actual coronal environment is complex, the effects of density and magnetic field structures on the plasma environment surrounding the radio source are not yet fully understood. In particular, the source region in the HF band (3-30 MHz) is located near the boundary between the solar corona and interplanetary space where the density and magnetic field structures drastically change. However, the number of SRB II observations in this frequency band is limited, and the SRB generation mechanism in the lower corona remains a challenge in solar physics.
In this study, we used multiple radio observational datasets—the Iitate Jupiter-Galaxy Radio Observatory HF band antenna (13.8–41.2 MHz) [Kumamoto et al., IUGONET workshop, 2011]; Learmonth Observatory (25–180 MHz) [the USAF RSTN; Kennewell & Steward, 2003]; IPRT/AMATERAS (100–500 MHz) [Iwai et al., 2012]; and Yamagawa Radio Observatory (70–9000 MHz) [NICT]—and coronagraph observational data from SOHO/LASCO-C2 (2.0–6.0 Rs) [Brueckner et al., 1995] to analyze the SRB event. The radio emission associated with the CME/flare occurred at 03:12 UT on 13 June 2022. We observed two SRB II emission lanes accompanying the CME at 14–17.5 MHz and 25–36 MHz between 03:25:20 and 03:33:00 UT,. These are in a fundamental and second harmonic relationship, respectively. In the harmonic emission lane, the higher power threshold was set, and the larger frequency drift rate rapidly increased after 03:28:50 UT. It was possible that the burst source regions where electrons were efficiently accelerated by shock drift acceleration [e.g., Holman and Pesses, 1983; Ball and Melrose, 2001] and the electron velocity distribution were varied due to the interaction between the coronal magnetic field and the CME shock wave. This is considered to be caused by a change in the magnetic field and density structures along the CME propagation path due to open magnetic field lines emerging from a coronal hole near the CME source region [e.g., Kong et al., 2012]. Similarly, after 03:28:50 UT, band-splitting SRB II emission that had been radiated from the downstream of the shock was not observed. Because the frequency gap of the band-splitting is associated with the shock-compression ratio, it was conceivable that the ratio of the magnetic field strengths downstream and upstream of the shock approached unity, or that the shock weakened during its interaction with the open magnetic field lines [e.g., Mann et al., 1995; Vršnak et al., 2002; Mahrous et al., 2018]. In this presentation, we will discuss the interaction between the CME shock wave and the coronal magnetic field structure. We also examine the elementary physical processes that are estimated from the spectral features, taking into account the changes in the magnetic field structure along the CME propagation path.
In this study, we used multiple radio observational datasets—the Iitate Jupiter-Galaxy Radio Observatory HF band antenna (13.8–41.2 MHz) [Kumamoto et al., IUGONET workshop, 2011]; Learmonth Observatory (25–180 MHz) [the USAF RSTN; Kennewell & Steward, 2003]; IPRT/AMATERAS (100–500 MHz) [Iwai et al., 2012]; and Yamagawa Radio Observatory (70–9000 MHz) [NICT]—and coronagraph observational data from SOHO/LASCO-C2 (2.0–6.0 Rs) [Brueckner et al., 1995] to analyze the SRB event. The radio emission associated with the CME/flare occurred at 03:12 UT on 13 June 2022. We observed two SRB II emission lanes accompanying the CME at 14–17.5 MHz and 25–36 MHz between 03:25:20 and 03:33:00 UT,. These are in a fundamental and second harmonic relationship, respectively. In the harmonic emission lane, the higher power threshold was set, and the larger frequency drift rate rapidly increased after 03:28:50 UT. It was possible that the burst source regions where electrons were efficiently accelerated by shock drift acceleration [e.g., Holman and Pesses, 1983; Ball and Melrose, 2001] and the electron velocity distribution were varied due to the interaction between the coronal magnetic field and the CME shock wave. This is considered to be caused by a change in the magnetic field and density structures along the CME propagation path due to open magnetic field lines emerging from a coronal hole near the CME source region [e.g., Kong et al., 2012]. Similarly, after 03:28:50 UT, band-splitting SRB II emission that had been radiated from the downstream of the shock was not observed. Because the frequency gap of the band-splitting is associated with the shock-compression ratio, it was conceivable that the ratio of the magnetic field strengths downstream and upstream of the shock approached unity, or that the shock weakened during its interaction with the open magnetic field lines [e.g., Mann et al., 1995; Vršnak et al., 2002; Mahrous et al., 2018]. In this presentation, we will discuss the interaction between the CME shock wave and the coronal magnetic field structure. We also examine the elementary physical processes that are estimated from the spectral features, taking into account the changes in the magnetic field structure along the CME propagation path.