Solar origin of near-relativistic impulsiveelectron events

There is increasing evidence suggesting that coronal acceleration supplies at least part of the particles observed during solar energetic particle events, yet coronal processes tend to be mostly disregarded in these studies. This is often due to the fact that the coronal restructuring in the early development of the associated flare and/or coronal mass ejection event is extremely fast (on the order of a few minutes) and can encompass most of the solar disk, thus requiring a full disk solar imager with very high time-cadence, and wide spectral coverage. An important subset of the energetic particle events are the near-relativistic impulsive electron events detected near Earth: their onsets can be traced back to a release time in the low corona with accuracies on the order of a couple of minutes. We investigate a series of impulsive electron events from 1998 to 2001 using energetic electron data measured in situ by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer (ACE) spacecraft, and radio coronal observations from the Nanqay Radioheliograph, the Decametric Array from Nanqay and the WAVES experiment on the WIND spacecraft. EPAM measures electrons in the energy range from 40 to 300 keV over a wide range of look directions and with better than 1 minute time resolution, while the Nançay radioheliograph provides images of the solar corona at 5 different frequencies with time cadence of 8 images per second and per frequency. This study focuses on the events which correspond to a delay, between the inferred injection times of the electrons at the Sun, and the electromagnetic emissions from flares, of at least 5 minutes. Radio signatures are found near the estimated time of the electron release for each of the events. The timing and spectral characteristics of the radio emissions, when compared with the properties of the particles seen at EPAM, strongly support an acceleration process in the corona but at highly variable heights from one event to the other.     

两个临近脉冲型太阳能量电子事件的观测与拟合

WIND飞船在2010年11月15日观测到两个临近的脉冲型太阳能量电子事件, 这两个事件在1AU处呈现出不同类型的通量-时间曲线. 事件一的通量表现出快速上升及快速下降的特性; 事件二则表现为缓慢上升, 更缓慢下降, 事件二的持续时间是事件一的5～17倍. 以往的解释认为事 件二中的电子在行星际受到了更强的散射. 本文引入等腰三角形的释放函数并 求解电报方程, 利用得到的解对1AU处的观测进行拟合. 根据最佳拟合结果 反推两事件在太阳上的释放函数和在行星际传播的平均自由程, 发现造成两事 件在1AU处能谱和通量-时间曲线形状不同的原因是太阳上电子 加速过程的不同而非行星际散射. 结合SOHO卫星的白光观测, 发现两事件可能 与一个CME (日冕物质抛射)相关, 并进一步推测了这两个太阳电子事件可能 的加速图像.      

Onset study of impulsive solar energetic particleevents

Impulsive solar energetic particle (SEP) events are associated with impulsive X-ray flares, energetic electrons,and enhanced heavy ion abundances. Using instruments on ACE, we have examined the composition and origin of twelve impulsive SEP events from November 1997 to June 2000. All selected impulsive SEP events have enhanced ³He/⁴He ratios compared with the solar wind values. The range of ³He/⁴He ratios varies from 0.01 to 7.8. By assuming scatter-free propagation at zero degree pitch-angle, we fitted the minimum particle path lengths (from 1.2 to 1.4 AU, as expected), and estimated the ion event release time back at the Sun to within better than 30 minutes in most cases. We found only four events in which the release times agree for both 38–50 keV electrons and <1 MeV/nucleon ions. Five of our events have significant differences (>40 minutes) between the electron and ion onset times, all with ions injected later. Three impulsive ion events have no association with any impulsive electron event. Seven events have associated solar electromagnetic signatures (Type III radio bursts and/or X-ray flares).     

A statistical study of solar radio Type III bursts and space weather implication

Solar radio bursts (SRBs) are the signatures of various phenomenon that happen in the solar corona and interplanetary medium (IPM). In this article, we have studied occurrence of Type III bursts and their association with the Sunspot number. This study confirms that occurrence of Type III bursts correlate well with Sunspot number. Further, using the data obtained using e-CALLISTO network, we have investigated drift rates of isolated Type III bursts and duration of the group of Type III bursts. Since Type II, Type III and Type IV bursts are signatures of solar flares and/or CMEs, we can use the radio observations to predict space weather hazards. In this article, we have discussed two events that have caused near Earth radio blackouts. Since e-CALLISTO comprises more than 152 stations at different longitudes, we can use it to monitor the radio emissions from the solar corona 24 h a day. Such observations play a crucial role in monitoring and predicting space weather hazards within few minutes to hours of time.     

Origin of coronal and interplanetary shock and particle acceleration of a flare/CME event

By using radio data from ground-based telescopes (from 270 MHz to 25 MHz), and from the Radio and Plasma Wave experiment (WAVES) on board the WIND spacecraft (1–14 MHz and several kHz-11 MHz), as well as FY -2 satellite data, the origin of coronal and interplanetary shock and particle acceleration of the 14 July 2000 flare/CME event (the Bastille day event) have been studied. Main conclusions are as follows: (1) We investigate the causal relationship between metric type 11 bursts observed by the digital IZMIRAN radio spectrograph and type II radio emissions in the frequency range from 1–14 MHz and several kHz-11 MHz observed by the WAVES/WIND. The analysis indicate that the fast CME is the origin of both coronal and interplanetary shocks. (2)According to the time profiles of Hard X-ray, and energetic particles (include proton, ³He, and ⁴He) from FY-2 satellite, it is obvious that the Bastille day event is the event, in which both impulsive and gradual phenomena occur. The energetic particles accelerated not only in flare but also in CME.     

RHESSI and radio imaging observations of microflares

We present an analysis of five microflares, three observed simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph (NoRH) in microwaves (17 GHz) and two observed by RHESSI and Nancay RadioHeliograph (NRH) at metric wavelengths (150–450 MHz). Since we have no radio imaging telescopes simultaneously operating at microwave and meter wavelengths in the same time zone, we are obliged to use a different set of metric events in contrast to that used for comparison with the two radio wavelengths. We are interested in using the locations and other imaging characteristics of the events from both RHESSI and radio observations instead of just temporal correlation. So we have used the Nancay (France) metric radioheliograph at 150–450 MHz for this purpose. Here we describe the properties of five events – three in microwaves and two at metric wavelengths. We discuss the brightness temperatures, emission measures and the hard X-ray spectral properties of these microevents. One sees small (mini) flaring loops clearly in NoRH and RHESSI images. The microwave emission often seems to come from the RHESSI foot points (for higher energies), and from the entire small (mini) flaring loop (for lower energies).The RHESSI microflares seem to be associated in position with metric type III bursts. Frequently, the hard X-ray spectrum of the microwave associated RHESSI microflares can be fit by a thermal component at low energies (∼3–12 keV) and a nonthermal component at higher energies (∼12–20 keV).     

Radio fine structures in dm–cm wavelength range associated with magnetic reconnection processes

Radio bursts with fine structures in decimetric–centimetric wave range are generally believed to manifest the primary energy release process during flare/CME events. By spectropolarimeters in 1–2 GHz, 2.6–3.8 GHz, and 5.2–7.6 GHz at NAOC/Huairou with very high temporal (1.25–8 ms) and spectral (4–20 MHz) resolutions, the zebra patterns, spikes, and new types of radio fine structures with mixed frequency drift features are observed during several significant flare/CME events. In this paper we will discuss the occurrence of radio fine structures during the impulsive phase of flares and/or CME initiations, which may be connected to the magnetic reconnection processes.     

Escaping near-relativistic electron beams from the solar corona

Processes in the solar corona are prodigious accelerators of energetic ions, and electrons. The angular distribution, composition, and spectra of energetic particles observed near Earth gives information on the acceleration mechanisms. A class of energetic particle observations particularly useful in understanding the solar acceleration is the near-relativistic impulsive beam-like electron events. During five years of operation the Advanced Composition Explorer (ACE) has measured well over 400 electron events. Approximately 25% of these electron events are impulsive beam-like events that are released onto interplanetary field lines predominantly from western solar longitudes. We extend our initial 3 year study during the rise to solar maximum (Haggerty and Roelof, 2002; Simnett et al., 2002) to a five year statistical analysis of these beam-like energetic electron events in relationship to optical flares, microwave emission, soft X-ray emission, metric and decametric type-III radio bursts, and coronal mass ejections.     

Hard X-ray and metric/decimetric spatially resolvedobservations of the 10 April 2002 solar flare

The GOES M8.2 flare on 10 April 2002 at 1230 UT was observed at X-ray wavelengths by RHESSI and atmetric/decimetric wavelengths by the Nançay Radioheliograph (NRH). We discuss the temporal evolution of X-ray sources together with the evolution of the radio emission sites observed at different coronal heights by the NRH. While the first strong HXR peak at energies above 50 keV arises from energy release in compact magnetic structures (with spatial scales of a few 10⁴ km) and is not associated with strong radio emission, the second one leads to energy release in magnetic structures with scales larger than 10⁵ km and is associated with intense decimetric/metric and dekametric emissions. We discuss these observations in the context of the acceleration sites of energetic electrons interacting at the Sun and of escaping ones.     

Radio observations of total solar eclipse of November 3, 1994 at Chapecó (Brzil)

Radio observations of the eclipse on November 3, 1994, were carried out at Chapecó, Brazil by using a decimetric spectrograph having high spectral and time resolution. The light curve shows that: (1) Time variation of the radio flux before the totality was more compared to that after. (2) During the totality radio emission at 1.5 GHz was observed. Advantage of high spatial resolution ( 3.2 arc sec) possible during solar eclipse enabled us to determine the height of radio emission at 1.5 GHz. (3) Microwave bursts were observed associated with metric Type III-RS bursts. The source size of one of the microwave bursts was 7 arc sec and its physical parameters have been estimated. (4) The time difference between radio and optical contacts suggested for the first time asymmetrical limb brightening at 1.5 GHz.     

VHF radio response of the near Earth space during solar activity growth in October, 2003

The analysis of observations of very high frequency radio noise intensity at the middle latitude on a frequency f = 500 MHz from 14th till 26th of October, 2003 is presented. These data are compared with the solar radio bursts in the range of frequencies 1–14 MHz registered by RAD2 receiver of the WAVES device installed on board the WIND spacecraft.     

High resolution time profile of decimetric type-III bursts

Type-III bursts are signatures of the electron beams accelerated during the solar flares, their observation and investigation provide information of the acceleration processes, the characteristics of the exciting agent and the acceleration site. The Brazilian Solar Spectroscope (BSS), in operation at INPE, Brazil, have recorded type-III radio bursts in decimetric range (2050–2250 MHz) with high time resolution of 20 ms. Decimetric reverse drift bursts are possibly generated in a dense loop by electron beams travelling towards the photosphere. Hence their time profiles should carry signatures of the density inhomogenities in the loop. Here the temporal and spectral characteristics of decimetric type-III bursts are presented.     

Noise in wireless systems from solar radio bursts

Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960–1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f  1 GHz (near current wireless bands), there can be a burst with amplitudes >10³ solar flux units (SFU; 1 SFU = 10⁻²² W/m²) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems.     

太阳射电微波爆发的频谱分析

1981年4月1日太阳发生一个4N级Hα耀斑并伴随出现强烈的IV型射电爆发.本文对北京天文台,西澳大利亚站等射电资料进行分析.分析表明:(1)该事件的微波源状态相对稳定,米波源位置存在移动,因此产生微波辐射与米波辐射是两组不同的电子群体,在爆发频谱指数的时变曲线上表现出明显的形态差异.还由于两者辐射源的位置不同,微波与米波的爆发在峰值时刻上也不完全符合.(2)4月1日微波大爆发是由三个主爆发组成的,它们的峰值时刻分别为0135.1,0146.1,0153.6UT.由射电高频端谱指数算出的非热电子能谱指数表明,在射电爆发的三个峰值时刻电子能谱都变硬.本文还得出该活动区的非热电子平均速度(以光速c为单位)β为0.9左右,磁场强度B为430G.并由回旋同步辐射阻尼算得,非热电子的寿命为829秒,这个数值与三个主峰的持续时间相吻合.     

Origin of complex type III-L events and electron acceleration

Type III-L bursts constitute a class of type III bursts that are intense, complex, and of long duration at hectometric wavelengths. They are often associated with major flares and fast coronal mass ejections. Several observations suggested that the electron beams that produce these complex hectometric emissions could be accelerated and injected in the low or in the middle corona. In this study, we revisit the origin of these bursts by tracing the progression of the events from the low corona to the interplanetary medium. We show that type III-L features are related to sudden changes in the radio emission observed at metric and decametric wavelengths, in particular the onset of new emitting sources at positions that can be at large distances from the flare site.     

HALE 17590 活动区的爆发辐射

本文根据1981年HALE 17590 太阳活动区的观测资料,着重分析了它的射电辐射特性后发现:(1)在光学活动区发展的上升阶段,每串射电爆发的强度也有由弱到强的变化,其频谱由单调谱变成不规则谱和U型谱;(2)对大的耀斑爆发而言,射电爆发的先兆相比X射线爆早。在射电先兆相期间常伴有谱斑增亮和暗条激活等现象;(3)大耀斑爆发的脉冲极大时刻在射电8毫米波段到来最早。      

Investigating the Coronal Mass Ejections associated with DH type-II radio bursts and solar flares during the ascending phase of the solar cycle 24

We studied a set of 74 CMEs, with shedding the light on the halo-CMEs (HCMEs), that are associated with decametric – hectometric (DH) type-II radio bursts (1–16?MHz) and solar flares during the period 2008–2014. The events were classified into 3 groups (disk, intermediate, and limb events) based on their longitudinal distribution.We found that the events are mostly distributed around 15.32° and 15.97° at the northern and southern solar hemispheres, respectively. We found that there is a clear dependence between the longitude and the CME’s width, speed, acceleration, mass, and kinetic energy. For the CMEs’ widths, most of the events were HCMEs (～62%), while the partial HCMEs comprised ～35% and the rest of events were CMEs with widths less than 120°. For the CMEs’ speeds, masses, and kinetic energies, the mean values showed a direct proportionality with the longitude, in which the limb events had the highest speeds, the largest masses, and the highest kinetic energies. The mean peak flux of the solar flares for different longitudes was comparable, but the disk flares were more energetic. The intermediate flares were considered as gradual flares since they tended to last longer, while the limb flares were considered as impulsive flares since they tended to last shorter.A weak correlation (R?=?0.32) between the kinetic energy of the CMEs and the duration of the associated flares has been noticed, while there was a good correlation (R?=?0.76) between the kinetic energy of the CMEs and the peak flux of the associated flares. We found a fair correlation (R?=?0.58) between the kinetic energy of the CMEs and the duration of the associated DH type-II radio bursts.     

射电爆发显著事件与Ⅱ型爆发

本文分析了北京天文台2840MHz射电望远镜,1989年1月-1993年12月期间观测到的太阳射电爆发的显着事件与米波Ⅱ型、Ⅳ型爆发的对应关系,从相关结果来看,爆发的峰值流量越高△T越短,这说明当太阳流量越大,高达500s.f.u.以上时,Ⅱ型爆发会在爆发的峰值前后很短时间内发生,可能与粒子的加速有关。      

Modulations of broad-band radio continua and X-ray emissions in the large X-ray flare on 03 November 2003

The GOES X3.9 flare on 03 November 2003 at ∼09:45 UT was observed from metric to millimetric wavelengths by the Nançay Radioheliograph (NRH), the Radio Solar Telescope Network (RSTN) and by radio instruments operated by the Institute of Applied Physics (University of Bern). This flare was simultaneously observed and imaged up to several 100 keV by the RHESSI experiment. The time profile of the X-ray emission above 100 keV and of the radio emissions shows two main parts, impulsive emission lasting about 3 min and long duration emission (partially observed by RHESSI) separated in time by 4 min. We shall focus here on the modulations of the broad-band radio continua and of the X-ray emissions observed in the second part of the flare. The observations suggest that gyrosynchrotron emission is the prevailing emission mechanism even at decimetric wavelengths for the broad-band radio emission. Following this interpretation, we deduce the density and the magnetic field of the decimetric sources and briefly comment on possible interpretations of the modulations.     

Cut-off features in interplanetary solar radio type IV emission

Solar radio type IV bursts can sometimes show directivity, so that no burst is observed when the source region in located far from the solar disk center. This has recently been verified also from space observations, at decameter wavelengths, using a 3D-view to the Sun with STEREO and Wind satellites. It is unclear whether the directivity is caused by the emission mechanism, by reduced radio wave formation toward certain directions, or by absorption/blocking of radio waves along the line of sight. We present here observations of three type IV burst events that occurred on 23, 25, and 29 July 2004, and originated from the same active region. The source location of the first event was near the solar disk center and in the third event near the west limb. Our analysis shows that in the last two events the type IV bursts experienced partial cut-offs in their emission, that coincided with the appearance of shock-related type II bursts. The type II bursts were formed at the flanks and leading fronts of propagating coronal mass ejections (CMEs). These events support the suggestion of absorption toward directions where the type II shock regions are located.