5:15 PM - 6:45 PM
[PEM16-P06] Motion of the source region of the type-II solar radio burst derived from the spectra in MF-HF frequency range
Keywords:Solar Radio Burst (SRB), Coronal Mass Ejection(CME), Space Weather
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]. Since the emission frequency of SRB II is determined by the local plasma frequency, the speed of CMEs propagating from the solar corona to interplanetary space can be estimated from the SRB II emission frequency by referring to the plasma density model (e.g. Pohjolainen et al., 2007). CMEs have a significant impact on the space environment around the Earth when they reach the Earth. Therefore, accurate prediction of the speed and the position of CMEs using the frequency-time variation of SRBs propagating at the speed of light is the key to dealing with space disasters.
In this study, we used the Waves observation data onboard the Wind satellite [0.02-14 MHz; Bougeret et al., 1995] and the HF-band monitor at the Iitate Jupiter Galaxy Radio Observatory owned by the Graduate School of Science, Tohoku University [15-40 MHz: Kumamoto et al., 2011] to estimate the speed and the position of SRB II source. We focused on the SRB II event observed on June 13, 2022. The SRB II event was associated with a CME that occurred at 03:12 UT and was observed in the 15-40 MHz band with a duration of about 10 minutes. Assuming that SRB II appeared in the spectra consist of the Fundamental and Harmonic lanes, we analyzed the emission frequency and its time evolution. Using the Baumbach-Allen model [Baumbach, 1938; Allen, 1947] multiplied by a factor of 10, the emission frequency of 36-25 MHz corresponds to 1.7-2.1 Rs (Rs is the solar radius) from the photosphere, and the source speed was estimated to be 250- 450 km/s. This result was in good agreement with the estimated speed of 200-500 km/s from SOHO/LASCO C2 and C3 images. Furthermore, the frequency drift rate of SRB II observed by the HF-band monitor showed a time variation. The estimated moving speed of the source was 200-320 km/s from 03:24:20 UT to 03:28:00 UT, while it increased to 300-450 km/s at 03:28:20-03:34:20 UT. CMEs are thought to be accelerated by radial pressure gradient forces due to solar wind generation [e.g., MacQueen & Fisher, 1983] and by the Lorentz force related to magnetic field structures in the corona [e.g., Chen & Krall, 2003]. The results of this study may correspond to time variation in burst source propagation speed due to CME acceleration. On the other hand, the Wind satellite observed SRB II at 1.8-14 MHz from 03:31:00 UT to 06:03:00 UT for about 2 hours and 30 minutes. The estimated speed was 150-220 km/s for all periods of the SRB II observation by Wind/Waves, which was smaller than the estimated speed from the HF-band monitor. To explain the difference between the estimated speeds, we need to consider the use of different density models for the 1.8-14 MHz frequency range corresponding to the interplanetary space as well as the evaluation of the estimation errors due to the time resolution of CME coronagraph images (6 or 12 minutes) from SOHO/LASCO C2 and C3 and errors in reading CME nose height. The validity of the assumption that the SRB II source was located at the CME nose also needs to be examined. Based on the analysis, we discuss the physical processes that determine the spectral structure and the motions of the CME and the burst source.
In this study, we used the Waves observation data onboard the Wind satellite [0.02-14 MHz; Bougeret et al., 1995] and the HF-band monitor at the Iitate Jupiter Galaxy Radio Observatory owned by the Graduate School of Science, Tohoku University [15-40 MHz: Kumamoto et al., 2011] to estimate the speed and the position of SRB II source. We focused on the SRB II event observed on June 13, 2022. The SRB II event was associated with a CME that occurred at 03:12 UT and was observed in the 15-40 MHz band with a duration of about 10 minutes. Assuming that SRB II appeared in the spectra consist of the Fundamental and Harmonic lanes, we analyzed the emission frequency and its time evolution. Using the Baumbach-Allen model [Baumbach, 1938; Allen, 1947] multiplied by a factor of 10, the emission frequency of 36-25 MHz corresponds to 1.7-2.1 Rs (Rs is the solar radius) from the photosphere, and the source speed was estimated to be 250- 450 km/s. This result was in good agreement with the estimated speed of 200-500 km/s from SOHO/LASCO C2 and C3 images. Furthermore, the frequency drift rate of SRB II observed by the HF-band monitor showed a time variation. The estimated moving speed of the source was 200-320 km/s from 03:24:20 UT to 03:28:00 UT, while it increased to 300-450 km/s at 03:28:20-03:34:20 UT. CMEs are thought to be accelerated by radial pressure gradient forces due to solar wind generation [e.g., MacQueen & Fisher, 1983] and by the Lorentz force related to magnetic field structures in the corona [e.g., Chen & Krall, 2003]. The results of this study may correspond to time variation in burst source propagation speed due to CME acceleration. On the other hand, the Wind satellite observed SRB II at 1.8-14 MHz from 03:31:00 UT to 06:03:00 UT for about 2 hours and 30 minutes. The estimated speed was 150-220 km/s for all periods of the SRB II observation by Wind/Waves, which was smaller than the estimated speed from the HF-band monitor. To explain the difference between the estimated speeds, we need to consider the use of different density models for the 1.8-14 MHz frequency range corresponding to the interplanetary space as well as the evaluation of the estimation errors due to the time resolution of CME coronagraph images (6 or 12 minutes) from SOHO/LASCO C2 and C3 and errors in reading CME nose height. The validity of the assumption that the SRB II source was located at the CME nose also needs to be examined. Based on the analysis, we discuss the physical processes that determine the spectral structure and the motions of the CME and the burst source.