题目：Coronal radio emission at 2-3 solar radii a new type of narrow-band bursts

　　报告人：Y. Voitenko, Solar-Terrestrial Center of Excellence, BIRA-IASB, Brussels, Belgium

　　摘要：I will discuss properties and possible emission mechanisms of narrow-band radio bursts discovered recently by world-largest Ukrainian radio telescopes UTR-2 and URAN-2. The burst frequencies 15-30 MHz and frequency drift rates 50-150 kHz/s imply emission sources propagating with near-Alfvén velocities at heliocentric distances 2-3 solar radii. Hence we will call them Alfvén-velocity (AV) bursts. AV bursts are associated with solar flares and coronal mass ejections, and occur simultaneously with or immediately after type III bursts. We propose a new generation mechanism for AV bursts elaborating properties of kinetic Alfvén waves (KAWs). KAWs can be excited by magnetic reconnection in the low corona and propagate upward generating local fluctuations of the plasma density. The KAW density cavities trap and accumulate Langmuir waves excited by electron beams. Enhanced Langmuir waves are progressively released in the course of upward KAW propagation and generate AV radio bursts by the plasma emission mechanism. KAWs with reasonable magnetic amplitudes about 0.03 of the background magnetic field and perpendicular wavelengths about 2-3 ion gyroradii provide a feasible explanation for observed AV bursts. These results can be used for remote diagnostics of the coronal plasma and waves during solar flares and CMEs. 　　

　　报告时间：2016年8月19日（星期五）10:00-11:00 　　

　　报告地点：紫台办公大楼317 会议室

欢迎大家积极参加！

　　                                                 紫金山天文台学术委员会