Japan Geoscience Union Meeting 2015

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International Session (Oral)

Symbol P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM07] Space Weather, Space Climate, and VarSITI

Mon. May 25, 2015 2:15 PM - 4:00 PM 302 (3F)

Convener:*Ryuho Kataoka(National Institute of Polar Research), Yusuke Ebihara(Research Institute for Sustainable Humanosphere, Kyoto University), Yoshizumi Miyoshi(Solar-Terrestrial Environement Laboratory, Nagoya University), Toshifumi Shimizu(Institute of Space and Astronautical Science, JAXA), Ayumi Asai(Unit for Synergetic Studies of Space, Kyoto University), Hidekatsu Jin(National Institude of Information and Communications Technology), Tatsuhiko Sato(Japan Atomic Energy Agency), Kanya Kusano(Solar-Terrestrial Environment Laboratory, Nagoya University), Hiroko Miyahara(College of Art and Design, Musashino Art University), Takuji Nakamura(National Institute of Polar Research), Kazuo Shiokawa(Solar-Terrestrial Environment Laboratory, Nagoya University), Kiminori Itoh(Graduate School of Engineering, Yokohama National University), Chair:Ryuho Kataoka(National Institute of Polar Research)

3:15 PM - 3:30 PM

[PEM07-23] Characteristics in solar white-light flares based on radio observations

*Satoshi MASUDA1, Jun KITAGAWA1, Kyoko WATANABE2 (1.Solar-Terrestrial Environment Laboratory, Nagoya University, 2.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency)

White-light flare is a solar flare in which an enhancement in white-light continuum is detected. Although most of white-light flares are large flares in energy like GOES X-class flare, it is not correct that only the amount of released energy determine if a solar flare becomes a white-light flare. To understand what generates a white-light flare, we analyzed 42 M- and X-class flares observed with Hinode/SOT during the period from January 2011 to August 2013. Among these 42 events, the number of white-light flares was 19. Comparing the white-light and no white-light events, we concluded that the key factor to generate white-light enhancement is the precipitation of large amount of nonthermal electrons within a short time duration into a compact region (Kitagawa et al., submitted to ApJ).
In this paper, we analyzed the 10 events (white-light: 4 events, no white-light: 6 events) among the 42 events, which were observed with Nobeyama Radio Heliograph (NoRH) and Nobeyama Radio Polarimeters (NoRP). GHz microwave are emitted by gyrosynchrotron from very-high energy (~MeV) accelerated electrons. The peak intensity in 17 and 35 GHz does not show any significant difference between the white-light and no white-light events. This indicates that such high-energy electrons does not contribute white-light enhancement. The spectrum of gyrosynchrotron emission usually has a peak frequency which corresponds to the turning point (turn-over frequency) between the optical thick part in the lower frequency range and the optically thin part in higher frequency range. The white-light flares show systematically high turn-over frequency than that of the no white-light events. The higher turn-over frequency might correspond to stronger magnetic field. This is consistent that white-light flares tend to be compact. As for the time evolution of the spectrum, the no white-light flares tend to show the spectral hardening. This indicates that the magnetic mirror effectively works in no white-light flares because of the weak magnetic field in the flare loop.