The relation between flare-related metric continuum bursts and coronal mass ejections

We describe a simple irradiance monitor intended for use in assessing the suitability of candidate sites for a worldwide network of small solar telescopes. The network will observe the Sun as continuously as possible in order to provide high quality solar oscillation data with low diurnal sidelobe contamination and high temporal frequency resolution.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

Type IV bursts and coronal mass ejections

The relationship of moving type IV bursts and coronal mass ejections (CMEs) is of interest, because it may yield insights into the origin and the physics of the ejecta. We discuss the statistical association of moving type IV bursts and CMEs, and find that about one-third to one-half of the IVs occur in association with CMEs, while only about 5% of the CMEs are accompanied by moving type IVs. We also find that the mean speed of the moving IVs is smaller than the mean speed of CMEs, and conclude that the type IVs move out with the bulk of the ejecta.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Peak flux of flares associated with coronal mass ejections

Features of flares that occur in association with coronal mass ejections(CMEs) have often displayed variations compared to flares with no associated CMEs. A comparative estimation of peak flux values of flares associated with CMEs and those without CMEs is made. Peak flux values of flares associated with CMEs show distinctly higher values in comparison to flares with no associated CMEs.Higher peak flux of CME associated flares may be attributed to the heating of plasma to higher temperature when associated with CMEs. While providing a distinct difference between the flux values of flares clearly associated with CMEs compared to flares associated with no CMEs, this study also highlights an evident difficulty in making distinct flare-CME associations.     

Properties of metre-wavelength solar bursts associated with coronal mass ejections

An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum bursts; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events.     

Spotless flares and type II radio bursts

Flares accompanied by type II meter radio bursts that occurred in plages with no visible spots are examined in this paper. There have been found 12 such spotless flares observed in the period of January 1981–August, 1990. Six out of all the flares may be said to have not been associated with any filament activation or disruption. A few of these flares have shown features of major events. The study suggests that a filament activation seems not to be the crucial factor for the occurrence of major flares in regions with no visible spots.     

Characteristics of coronal mass ejections associated with interplanetary shocks

In a correlated study using coronagraph and interplanetary data from 1978 to 1983, a set of 56 coronal mass ejections (CMEs) was confidently associated with interplanetary shocks by Sheeleyet al. (1985). In this paper we analyze the characteristics of these particular CMEs in contrast to the whole population of them during the period. We find that the associated CMEs are not a representative sample of all the variety of CMEs and that they share specific characteristics. Contrary to common beliefs, these characteristics are not a high velocity or a large extension, but have more to do with the importance and shape of the CME. Practically all the CMEs associated with shocks were of importance Y (bright and/or large) and had a curved-type front structural class (a continuous curved front with either straight edges or curved legs). Another common characteristic of these particular CMEs is that they show a considerable increase in their angular span as they go out from the Sun, moving the peak of the distribution from 30° to 70°.     

Solar mass ejections and coronal holes

In this paper we present observations of two types of solar mass ejections, which seem to be associated with the location of coronal, holes. In the first type, a filament eruption was observed near a coronal hole, which gave rise to a strong interplanetary scintillations. as detected by IPS observations. In the second type, several large scale soft X-ray blow-outs were observed in the YOHKOH SXT X-ray movies, in all the cases they erupted from or near the boundary of coronal holes and over the magnetic neutral line. It is proposed that the open magnetic field configuration of the coronal hole provides, the necessary field structure for reconnection to take place, which in turn is responsible for filament eruption, from relatively lower heights. While, in the case of X-ray blow-outs, the reconnection takes place at a greater height, resulting in high temperature soft X-ray emission visible as X-ray blow-outs.     

A positional comparison between coronal mass ejection events and solar type II bursts

An investigation is made to determine the positional relation between the leading edge of the coronal mass ejection (CME) and the source region of associated solar type II radio bursts. A preliminary relation between the optical and radio activity was first established for each event using projected starting times and positional data. Height - time plots were then deduced for the radio activity using radiospectrograph observations in conjunction with a variety of coronal density models. These plots were then compared with height - time plots for the leading edge of the associated CME events, which has been observed with the SOLWIND experiment aboard the P78-1 satellite. In 31 well-observed events a total of 13 (42%) had type II bursts which could confidently be placed near the leading edge of the CME. In these events the density model which gave the best agreement between CME and type II positions was five times the Saito (1970) quiet Sun model. The existence of these closely related events was further confirmed by direct positional comparisons for the event of 1979, May 4. In a further nine events the type II burst was seen within the CME but was located well behind the leading edge, suggesting that they were created by a blast wave. The remaining nine events had height - time plots which could not be accurately compared. The observations are discussed in relation to models for the CME and type II activity. We suggest that the type II is generated when the shock wave is formed within the closed field structure near the leading edge of the CME or, in the case of a blast wave, interacts with closed fields in the body of the transient.     

Homologous type II radio bursts and coronal transients

The homology of seven successive type II solar radio bursts, which occurred at the times of flares from an active region near the solar west limb on 1980, July 27–29, is described, together with evidence for coronal mass outflows accompanying these bursts. It is argued that homologous type II bursts imply that the corona is restructured in a similar manner by successive coronal transients.     

The onset of coronal mass ejections

This study addresses the onset of coronal mass ejections. From examination of sensitive X-ray images from the Solar Maximum Mission around the projected onset time of coronal mass ejections we identify two important new features: (1) there is usually a weak, soft X-ray enhancement 15–30 min prior to the linearly extrapolated chromospheric departure time of the ejection; (2) this activity is generally from two widely separated ( 10⁵ km) parts of the Sun. Possible physical mechanisms for these phenomena are examined and it is concluded that a plausible explanation is that the initial energy release is converted first into kinetic energy of suprathermal protons, 10²–10³ keV. The protons are trapped in a large magnetic loop which later breaks open as the mass ejection; Coulomb losses are the destabilizing agent but the mass ejection is probably magnetically driven. Protons that escape into the loss cone will impact the loop footpoints to heat the upper chromospheric material to a sufficiently high temperature to generate the weak soft X-ray emission. There will also be an H signature, and this is observed in a number of events. There is in general no radio emission or hard X-ray emission accompanying the soft X-ray precursor. When the coronal mass ejection is followed by a flare, then this is generally from a point close to, but not identical to, one of the points with the earlier soft X-ray enhancement.NCAR is sponsored by the National Science Foundation.     

Initiation and propagation of coronal mass ejections

This paper reviews recent progress in the research on the initiation and propagation of CMEs. In the initiation part, several trigger mechanisms are discussed; in the propagation part, the observations and modelings of EIT waves/dimmings, as the EUV counterparts of CMEs, are described.     

Visibility and rate of coronal mass ejections

Two thirds of the H flares associated in time and position with coronal mass ejections (CME) observed by the Coronagraph/Polarimeter (C/P) or by the coronagraph on Skylab lie within 30° of the solar limb. Among type II flares (those with type II radio spectral bursts) with C/P observations, 10 are within 10° of the limb and 8 of these are associated with CME. The high rate of CME association at the limb is interpreted here to imply: (1) Most type II flares (at least 80%) are physically associated with mass motion in the corona (although about half of CME flares lack type II bursts). (2) The longitude window, centered on the plane of the sky, within which C/P and Skylab coronagraphs detect CME has halfwidth of 20° to 30°. (3) CME observed at polar position angles are unlikely to be flare associated. (4) The total number of mass ejections must be considerably greater than the number detected. The ratio of total number to observed number is estimated to be between 2 and 3, and the total occurrence frequency of coronal mass ejections at solar-cycle maximum to be comparable to that of flares of importance 1. The clear dependence of CME detection on flare position implies that the location of the mass ejection must be well described by the location of the associated flare, and that the ejected mass must have limited longitudinal extent in the corona, comparable to the width of the detection window and to the directly observed latitudinal extent of 35° +- 15° for CME observed by C/P and the Skylab coronagraph.Much of the work reported here was done at the High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307, U.S.A. The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Characteristics of coronal mass ejection associated with DH type II radio bursts (All and Limb events)

We have studied the characteristics of coronal mass ejections (CMEs) associated with Deca-Hectometric (DH) type II radio bursts (1–14 MHz) in the interplanetary medium during the year 1997–2005. The DH CMEs are divided into two parts: (i) DH CMEs (All) and (ii) DH CMEs (Limb). We found that 65% (177/273) of all events have the speed >900 km?s^?1 and the remaining 35% (96/273) events have the speed below 900 km?s^?1. The average speed of all and limb DH CMEs are 1230 and 1288 km?s^?1, respectively, which is nearly three times the average speed of general population of CMEs (473 km?s^?1). The average widths of all and limb DH CMEs are 105° and 106°, respectively, which is twice the average width (52°) of the general population of CMEs. We found a better correlation between the speed and width of limb DH CMEs (R=?0.61) than all DH CMEs (R=?0.53). Only 28% (177/637) of fast >900 km?s^?1 general population of CMEs are reported with DH type II bursts counterpart. The above results gives that the relation between the CME properties is better for limb events.     

The relationship between the duration of solar X-ray flares and the mass of associated coronal ejections

The statistical relationship between the parameters of X-ray flares and coronal mass ejections on the Sun that are associated with these flares, is considered. It is shown that short X-ray flares are characterized on average by a lower mass ejection in the outer layers of the corona and interplanetary space as compared to high-energy long-duration events.     

Flares before and after coronal mass ejections

Flare characteristics such as the flare occurrence number density and the distribution of peak flux as well as duration of flares occurring on either side of a coronal mass ejection(CME) onset time are studied. While the flares are rather evenly distributed statistically on either side of the CME onset time,the flare peak flux and duration tend to decrease depending upon their occurrence either before or after the CME onset. This is consistent with the earlier findings that flares emit higher energy before a CME whereas the energy is less in flares occurring after a CME.     

Magnetic source regions of coronal mass ejections

The majority of flare activity arises in active regions which contain sunspots, while Coronal Mass Ejection (CME) activity can also originate from decaying active regions and even so-called quiet solar regions which contain a filament. Two classes of CME, namely flare-related CME events and CMEs associated with filament eruption are well reflected in the evolution of active regions. The presence of significant magnetic stresses in the source region is a necessary condition for CME. In young active regions magnetic stresses are increased mainly by twisted magnetic flux emergence and the resulting magnetic footpoint motions. In old, decayed active regions twist can be redistributed through cancellation events. All the CMEs are, nevertheless, caused by loss of equilibrium of the magnetic structure. With observational examples we show that the association of CME, flare and filament eruption depends on the characteristics of the source regions:

?the strength of the magnetic field, the amount of possible free energy storage,

?the small- and large-scale magnetic topology of the source region as well as its evolution (new flux emergence, photospheric motions, cancelling flux), and

?the mass loading of the configuration (effect of gravity). These examples are discussed in the framework of theoretical models.

     

Study of large solar energetic particle events with halo coronal mass ejections and their associated solar flares

The purpose of the present study is to investigate the association of solar energetic particle (SEP) events with halo coronal mass ejections (CME) and with their associated solar flares during the period 1997–2014 (solar cycle 23 and 24). We have found that halo CMEs are more effective in producing SEP events. The occurrence probability and peak fluxes of SEPs strongly depend on the halo CMEs speed (V) as follows. The highest associations, 56% for occurrence probability and 90% for average peak fluxes, are found for the halo CMEs with V> 1400 km s⁻¹ but the lowest associations, 20% for occurrence probability and 5% for average peak fluxes, are found for halo CMEs with speed range 600 ≤ V ≤ 1000 km s⁻¹. We have also examined the relationship between SEP events and halo CME associated solar flares and found that 73% of events are associated with western solar flares while only 27% are with eastern solar flares. For longitudinal study, 0–20° belt is found to be more dominant for the SEP events. The association of SEP events with latitudinal solar flares is also examined in the study. 51% of events are associated with those halo CMEs associated solar flares which occur in the southern hemisphere of the Sun while 49% are with those solar flares that occur in the northern hemisphere of the Sun. Also, 10–20° latitudinal belt is found to be likely associated with the SEP events. Further, 45% of SEP events are associated with M-class solar flares while 44% and 11% are with X and C-class respectively. Maximum number of SEP events are found for the fast halo CME associated X- class solar flares (68%) than M and C- class solar flares.