太阳耀斑环——射电微波及相关波段的研究

与大多以光学波段为主的耀斑研究不同的是,作者拟以射电微波(厘米波段)的频谱和成像观测为主及相应的辐射机制研究太阳活动的基本单元——耀斑环及其物理参数的空间分布和时间演化规律。特别是中国研制的具有国际最高的时间、空间和频率分辨率的射电日像仪(MUSER)已投入运行,文章将为推动该设备即将开展的科学研究提供重要的参考工具。此外,文中也加入了与射电微波辐射密切相关的X射线、紫外和光学波段的研究,符合太阳物理乃至整个天体物理多波段研究的大趋势。文章集中介绍作者最具特色的研究,由于篇幅所限只能给出基本物理思想和概念、主要结论和代表性插图,对相应的理论推导、观测数据处理等细节,读者可根据需要参阅对应的参考文献。     

Radio and EUV signatures of a solar flare-CME event on November 28, 1998

Using the observational data of the solar radio spectrometer with a broad bandwidth of the Chinese National Astronomical Observatories (CNAO), the Nobeyama Radio Heliograph (NoRH) and Polarimeters (NoRP), YOHKOH and SOHO satellites, it is found that there are two characteristics in an X3.3 flare event associated with coronal mass ejection (CME). (ⅰ) X-ray and EUV loop interaction and evolution appeared evidently in corona, followed by the formation of a twisted loop structure, which is consistent with the theoretical calculations of Amari et al. (1999a,b) for the origin of flare-CME events. (ⅱ) The slow frequency drift was shown in the radio observations, corresponding to the relevant movement of the radio source observed by NoRH, at a speed of several tens kilometers per second, which may be associated with the speed of the shock waves resulting from the CME.     

A Quasi-Periodic Solar Radio Fluctuation at Microwave Band

A rare but interesting solar radio fine structure, quasi-periodic fluctuations, on 25 August 1999 was observed at microwave band for the first time. They fluctuated initially at a nearly stable frequency level then at a reverse drift component up to 5.49 GHz, The individual fluctuation consists of a hi-directional drift component. The features are characterized by narrow bandwidth of △f/f≤3%, quasi-periodicity of ～ 100 ms as well as a slowly reverse and a rapidly normal drift rates on the hi-directional drift component. The associated data of the Yohkoh soft and hard x-ray telescope and Nobeyama radio heliograph at 17GHz showed that there are several bright spots （i.e. inhomogeneities） along the soft x-ray loop, and the locations of both radio and soft x-ray sources are closely consistent. Therefore, the fluctuations are most likely caused by the inhomogeneities within a flare loop. Based on the two-component atmospheric model, we suggest a three-component atmospheric model with large scale length λ and small scale lengths λ1 and λ2 to describe equilibrium atmosphere and inhomogeneity. With the beam model, the characters of fluctuations may be interpreted reasonably by the quasi-equidistant inhomogeneity along a flare loop.     

A pair of solar spike emissions

Using the 2.6-3.8 GHz solar radio spectrometer of the National Astronomical Observatories of China (NAOC), a pair of microwave millisecond spike (MMS) emissions were observed, and their frequency drift rate was measured. The separatrix frequency of the MMS pair was at 2900 MHz. Its emission layer was about 2×104km above the photosphere. The polarization degree was wave-like variation with an average value of about 25% in LCP. An MMS pair differs greatly from the type III bursts pair. For the latter, in a certain frequency range, there is no emission around separatrix frequency. This phenomenon may help better understand the mechanism of MMS.     

非线性撕裂模的时间演化

本文在有理面附近的局域近似下,从MHD方程出发,求出了非线性撕裂模的时间演化的解析结果。大体可划分为三个阶段:线性增长,由非线性因素导致饱和,最终过渡到一个与初始条件无关的非线性特解,并与原有的线性及非线性撕裂模的解析结果进行了比较,在线性近似下可退化到经典的结果。由本文结论还可解释托卡马克的大破裂中的有关现象。 关键词：     

Effect of Electron Drift Velocity on Whistler Instability in Collisionless Magnetic Reconnection

The whistler instability is studied under the condition that the electron and ion velocities can be described in a bi-Maxwellian distribution with a field-aligned electron outflow drift velocity. It is found that the electron outflow drift velocity might obviously make the threshold condition of whistler instability decrease when this velocity is parallel to the magnetic field, whereas the electron outflow drift velocity might increase the threshold condition when this velocity is anti-parallel to the magnetic field in collisionless magnetic reconnection.