摘要
太阳米波和分米波的射电观测是对太阳爆发过程中耀斑和日冕物质抛射现象研究的重要观测手段。米波和分米波的太阳射电暴以相干等离子体辐射为主导,表现出在时域和频域的多样性和复杂性。其中Ⅱ型射电暴是激波在日冕中运动引起电磁波辐射的结果。在Ⅱ型射电暴方面,首先对米波Ⅱ型射电暴的激波起源问题和米波Ⅱ型射电暴与行星际Ⅱ型射电暴的关系问题进行了讨论;其次,结合Lin-Forbes太阳爆发理论模型对Ⅱ型射电暴的开始时间和起始频率进行讨论:最后,对Ⅱ型射电暴信号中包含的两种射电精细结构,Herringbone结构(即鱼骨结构)和与激波相关的Ⅲ型射电暴也分别进行了讨论。Ⅲ型射电暴是高能电子束在日冕中运动产生电磁波辐射的结果。在Ⅲ型射电暴方面,首先介绍了利用Ⅲ型射电暴对日冕磁场位形和等离子体密度进行研究的具体方法;其次,对利用Ⅲ型射电暴测量日冕温度的最新理论进行介绍;最后,对Ⅲ型射电暴和Ⅱ型射电暴的时间关系、Ⅲ型射电暴和粒子加速以及Ⅲ型射电暴信号中包含的射电精细结构(例如斑马纹、纤维爆发及尖峰辐射)等问题进行讨论并介绍有关的最新研究进展。
Observations and studies of solar eruptions in radio wavelengths provide us several diagnostic approaches to answering longstanding questions about shocks, particle accelerations, and particle transports in magnetized plasmas. At decimetric and metric wavelengths, coherent plasma radiation plays a dominant role in observed radio emissions. Coronal mass ejections （CMEs） and solar flares play a pivotal role in the solar terrestrial relationship： they are responsible for major geomagnetic storms and the event of solar energetic particles （SEPs）. It is now generally accepted that type Ⅱ and type Ⅲ radio bursts in the solar eruption are closely related to flares and CMEs.
Type II radio bursts are the slow frequency drifting signature in the dynamic spectrum. It is interpreted as the result of the outward motion of the fast mode shock driven by CME. Type Ⅲ radio bursts, on the other hand, are the fast frequency drifting signature in the dynamic spectrum. Usually they are interpreted as the radio signature of energetic electron beams propagating along the magnetic field outward through the corona or interplanetary space at speed of 0.2-0.6 c. The reverse frequency drifting type III radio bursts and the U-shape radio bursts are sometimes observed as well. The reversedrifting type III radio bursts are believed to result from the Sunward energetic electron beams, and the Ushape radio bursts are due to electron beams propagating in a closed magnetic loop. Moreover, groups of type Ⅲ radio bursts are observed in some special events and they are interpretedas electron beams trapped in moving plasmoids, which are constrained inside semiclosed magnetic field structures
In this work, we first introduce four kinds of type Ⅱ radio bursts： （1） the type II radio bursts that include the third component of the plasma emission, （2） the type II burst with high starting frequency, （3）the bifurcation metric type Ⅱ radio burst, and （4） the type Ⅱ radio burst of nearly zero frequency drift. We discussed three aspects about the typeⅡ radio burst that have long drawn attention of the community： （1） the origin of the metric typeⅡ radio burst, （2） the relation of the metric type Ⅱ radio burst to that in the interplanetary medium, and （3） the onset positions and frequencies of the type Ⅱ Vradio burst that are dependent on the local Alfvdn speed and the rate of magnetic reconneetion. Then, we looked into two kinds of different fine structures about shockassociated type Ⅲradio burst （SA） and the herringbone structures. Both of them are associated with typeⅡ radio bursts as the signal of particle accelerations by the CMEdriven shock.
In the third part of this work, we introduce the details of the type Ⅲ radio burst, which is used for diagnosing the coronal magnetic field structure and the coronal plasma density. According to recent numerical experiments, type Ⅲ radio bursts may as well offer a new tool to probe both distributions or structures of Te and Ti in the corona. We discuss two issues of the type Ⅲ burst that are related to other activities and phenomena： （1） the time sequence of typeⅡ and type III radio bursts, （2） On the basis of the catastrophe model of solar eruptions, particles can be accelerated in current sheet, and produce type Ⅲ radio bursts, therefore the starting frequency of the type Ⅲ burst should decrease with time since the current sheet continues to move upward in eruption. This is related to the motion of the flare loop system in the eruption. We also introduce and discuss three kinds of fine structures that are always found associated with type Ⅲ radio bursts： zebra, fiber as well as spike, and emphasized the relationship among typeⅢ radio bursts, spikes and hard Xray emissions in solar eruptions. Finally, we introduce two new solar radio digital spectrographs （70-700 MHz and 625-1 500 MHz） with high frequency （200 kHz） and high time （80 ms） resolutions at the Yunnan Astronomical Observatory, China, and some observations made by them.
出处
《天文学进展》
CSCD
北大核心
2012年第1期35-47,共13页
Progress In Astronomy
基金
国家自然科学基金(10873030
10978006)
973计划(2011CB811403)
中国科学院太阳活动重点实验室基金
