[P-EM27_1PO1] Heliosphere and Interplanetary Space

[PEM27-P04] Fine spectral structures of a solar radio type-II burst observed with AMATERAS

Shintaro SATO¹, *Hiroaki MISAWA¹, Fuminori TSUCHIYA¹, Takahiro OBARA¹, Kazumasa IWAI², Satoshi MASUDA³, Yoshizumi MIYOSHI³ (1.PPARC, Tohoku Univ., 2.Nobeyama Solar Radio Observatory, NAOJ, 3.STE Lab., Nagoya Univ.)

Keywords:Sun, radio wave, type-II burst, fine structure, generation process

Solar radio type-II bursts are metric to hectometric radio bursts that show frequency drifting spectral structures caused by the plasma emission from shock-accelerated electrons. The bursts are known to sometimes show rapidly drifting fine structures; for example, about 20% of type-II bursts are composed of both negative and positive rapidly drifting elements, which are called as "herringbone" structure (hereafter HB) [Roberts, 1959]. Such the drifting fine structures are interpreted as the motion of non-thermal energetic electron beams accelerated by the shock. However, their particle acceleration mechanisms and regions have not been understood well. The purpose of this study is to extract characteristics of the fine spectral structures of type-II bursts from high-resolution observations and investigate their acceleration processes. AMATERAS is a ground-based solar radio receiving system developed in 2010 by Tohoku University [Iwai et al., 2012]. This system enables us to observe radio phenomena in 150 - 500 MHz with the 10 ms accumulation time and 61 kHz bandwidth. So far some type-II bursts with fine spectral structures have been observed. Among them, a type-II burst observed on November 12, 2010 around 200MHz showed distinctive fine structures whose spectral characteristics were different from those of HB. The fine structures showed no core structure which were normally confirmed in HB, but showed various rapidly drifting nature and composed whole body of a slowly negative-drifting type-II burst. The statistical drift rate analysis showed that negative drift cases were dominant and some of them indicated more than 100MHz/s. The particle speed for the drift rate by assuming a general coronal plasma density model, for example the Newkirk model [Newkirk, 1961], is estimated to be unrealistically fast. This implies that the rapidly drifting fine structures were generated by energetic electron beams in an outward moving steep density gradient region such as a shock front. In this presentation, we will show revealed statistical characteristics of the fine structures and discuss inferred generation processes of the type-II burst. We will also introduce characteristics of fine spectral structures of the other events of type-II burst.