scholarly journals Dynamic Events in the X-Ray Corona (A Progress Report from the AS&E X-ray Telescope on Skylab)

1974 ◽  
Vol 57 ◽  
pp. 501-504 ◽  
Author(s):  
G. S. Vaiana ◽  
A. S. Krieger ◽  
J. K. Silk ◽  
A. F. Timothy ◽  
R. C. Chase ◽  
...  
Keyword(s):  
Active Region ◽  
Large Scale ◽  
Active Regions ◽  
Loop Structure ◽  
X Ray ◽  
Dynamic Events ◽  
Coronal Bright Points ◽  
Coronal Activity ◽  
East Limb ◽  
Coronal Structures

Data obtained by the AS&E X-ray Telescope Experiment during the first Skylab mission have revealed a variety of temporal changes in both the form and brightness of coronal structures. Dynamical changes have been noted in active regions, in large scale coronal structures, and in coronal bright points. The coronal activity accompanying a series of Hα flares and prominence activity between 0800 and 1600 UT on 10 June 1973 in active region 137 (NOAA) at the east limb is shown in Figure 1. It is characterized by increases in the brightness and temperature of active region loops and a dramatic change in the shape and brightness of a loop structure. Figure 2 shows the reconfiguration of an apparent polar crown filament cavity between 1923 UT on 12 June 1973 and 1537 UT on 13 June 1973. A ridge of emitting material which attains a peak brightness at least four times that of the surrounding coronal structures appears within the cavity during the course of the event. Typical X-ray photographs with filters passing relatively soft X-ray wavelengths (3–32, 44–54 Å) show 90 to 100 X-ray bright points (Vaiana et al., 1973). On twelve occasions in the data from the first mission, such bright points were seen to increase in intensity by two orders of magnitude in less than 4 min. Such an event is shown in Figure 3.

scholarly journals Variations of the Coronal Radiation in X-ray Related to Coronal Holes, Active Region Loop Systems, Bright Points

1994 ◽  
Vol 143 ◽  
pp. 159-171
Author(s):  
Ester Antonucci
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Large Scale ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Small Scale ◽  
X Ray ◽  
Coronal Structures

The coronal features observed in X-ray emission, varying from the small-scale, short-lived bright points to the large-scale, long-lived coronal holes, are closely associated with the coronal magnetic field and its topology, and their variability depends strongly on the solar cycle. Here we discuss the spatial distribution of the coronal structures, the frequency distribution of the brightness variations in active regions, and the role of magnetic reconnection in determining the variability of the coronal features, on the basis of the new observations of the soft X-ray emission recently obtained with the Yohkoh satellite and the NIXT experiment.

Mass and Energy Flow in the Solar Atmosphere Implications of Skylab Observations

1977 ◽  
Vol 36 ◽  
pp. 263-315
Author(s):  
George L. Wlthbroe
Keyword(s):  
Solar Atmosphere ◽  
Energy Flow ◽  
Large Scale ◽  
Strong Field ◽  
Coronal Holes ◽  
Active Regions ◽  
Weak Field ◽  
X Ray ◽  
The North ◽  
East Limb

The Skylab experiments acquired a wealth of observations applicable to investigating problems associated with the mass and energy flow in the solar atmosphere. In this review we discuss some of the observations of quiet regions, coronal holes and active regions and Illustrate the fundamental role that magnetic fields play in defining the structure and the mass and energy flow in these regions. Figure 1 (Altschuler et al., 1976) illustrates three major classes of structure: (1) strong field, magnetically closed areas typified by active regions, (2) weak field, open regions which, according to present evidence, appear to be associated primarily with coronal holes, and (3) weak field regions which appear to be magnetically closed on a large scale and appear to be associated primarily with normal quiet areas. Some of these latter structures can be seen in the X-ray photograph presented in Figure 2 (Vaiana et al., 1973a). Also evident in this figure are large coronal holes near the east limb at the north pole.

scholarly journals X-Ray Structures Associated with Disappearing Hα Filaments in Active Regions

1980 ◽  
Vol 91 ◽  
pp. 61-65
Author(s):  
S. W. Kahler
Keyword(s):  
Active Region ◽  
Large Scale ◽  
Active Regions ◽  
Statistical Correlation ◽  
Coronal Emission ◽  
X Ray ◽  
Temporal Relationships ◽  
Using Data ◽  
Scale Length ◽  
Shape And Size

Several studies using data from Skylab instruments have been carried out to determine the spatial and temporal relationships between disappearing Hα filaments and the associated coronal emission features. Webb et al. (1976) studied 30 transient coronal X-ray enhancements which could be associated with the disappearances of Hα filaments outside active regions. They found that in the early phase of the transient X-ray brightening, emitting structures appeared at or near the filament location with shape and size resembling the filament. Sheeley et al. (1975) examined a long-lived X-ray enhancement of expanding loops associated with an active region filament which disappeared. Rust and Webb (1977) found a good statistical correlation in time and position between large scale (length > 60, 000 km) active region X-ray enhancements and Hα filament activity, in particular, events of an eruptive nature.

scholarly journals Statistical Properties of Magnetic Separators in Model Active Regions

2000 ◽  
Vol 195 ◽  
pp. 443-444
Author(s):  
B. T. Welsch ◽  
D. W. Longcope
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
First Principles ◽  
Magnetic Charge ◽  
Active Regions ◽  
Heating Rates ◽  
X Ray ◽  
Field Lines ◽  
Charge Topology

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

scholarly journals Modelling of Solar Coronal Loops

1992 ◽  
Vol 9 ◽  
pp. 661-662
Author(s):  
C. Jordan
Keyword(s):  
Energy Balance ◽  
Active Region ◽  
Active Regions ◽  
Coronal Loops ◽  
Loop Structure ◽  
X Rays ◽  
Spectroscopic Observations ◽  
Available Information ◽  
Solar Coronal

Modelling of coronal active regions in terms of loop structures began around 1974 (see Jordan 1975) and was stimulated by images of the corona in X-rays and the uv, obtained from rocket flights. Vaiana was a pioneer in this field (see Vaiana et al. 1973). The Skylab missions provided a fuller range of imaging and spectroscopic observations, and much of the available information is still based on these data (see Orrall 1981). Since 1975 a very large number of papers have been published on the various aspects of loop structure, heating and stability (see review by Mewe 1991). Here I can mention only a few points concerning the relation between observable parameters and the energy balance and heating requirements of active region loops.

scholarly journals Joint Discussion 3 Solar active regions and 3D magnetic structure

2006 ◽  
Vol 2 (14) ◽  
pp. 139-168
Author(s):  
Debi Prasad Choudhary ◽  
Michal Sobotka
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Large Scale ◽  
Focal Point ◽  
Active Regions ◽  
Theoretical Modelling ◽  
Solar Chromosphere ◽  
Origin And Evolution ◽  
Solar Active Regions ◽  
The Magnetic Field

AbstractKeeping in view of the modern powerful observing tools, among othersHinode(formerlySOLAR-B),STEREOand Frequency-Agile Solar Radiotelescope, and sophisticated modelling techniques, Joint Discussion 3 during the IAU General Assembly 2006 focused on the properties of magnetic field of solar active regions starting in deep interior of the Sun, from where they buoyantly rise to the coronal heights where the site of most explosive events are located. Intimately related with the active regions, the origin and evolution of the magnetic field of quiet Sun, the large scale chromospheric structures were also the focal point of the Joint Discussion. The theoretical modelling of the generation and dynamics of magnetic field in solar convective zone show that the interaction of the magnetic field with the Coriolis force and helical turbulent convection results in the tilts and twists in the emerging flux. In the photosphere, some of these fluxes appear in sunspots with field strengths up to about 6100 G. Spectro-polarimetric measurements reveal that the line of sight velocities and magnetic field of these locations are found to be uncombed and depend on depth in the atmosphere and exhibit gradients or discontinuities. The inclined magnetic fields beyond penumbra appear as moving magnetic features that do not rise above upper photospheric heights. As the flux rises, the solar chromosphere is the most immediate and intermediary layer where competitive magnetic forces begin to dominate their thermodynamic counterparts. The magnetic field at these heights is now measured using several diagnostic lines such as CaII854.2 nm, HI656.3 nm, and HeI1083.0 nm. The radio observations show that the coronal magnetic field of post flare loops are of the order of 30 G, which might represent the force-free magnetic state of active region in the corona. The temperatures at these coronal heights, derived from the line widths, are in the range from 2.4 to 3.7 million degree. The same line profile measurements indicate the existence of asymmetric flows in the corona. The theoretical extrapolation of photospheric field into coronal heights and their comparison with the observations show that there exists a complex topology with separatrices associated to coronal null points. The interaction of these structures often lead to flares and coronal mass ejections. The current MHD modelling of active region field shows that for coronal mass ejection both local active region magnetic field and global magnetic field due to the surrounding magnetic flux are important. Here, we present an extended summary of the papers presented in Joint Discussion 03 and open questions related to the solar magnetic field that are likely to be the prime issue with the modern observing facilities such asHinodeandSTEREOmissions.

Soft X-ray observations of large-scale coronal active region brightenings

Solar Physics ◽  
1977 ◽  
Vol 54 (2) ◽  
pp. 403-417 ◽  
Author(s):  
David M. Rust ◽  
David F. Webb
Keyword(s):  
Active Region ◽  
Large Scale ◽  
X Ray

scholarly journals Distinguishing between flaring and nonflaring active regions

2020 ◽  
Vol 639 ◽  
pp. A44
Author(s):  
Soumitra Hazra ◽  
Gopal Sardar ◽  
Partha Chowdhury
Keyword(s):  
Active Region ◽  
Magnetic Flux ◽  
Time Evolution ◽  
Large Scale ◽  
Learning Algorithm ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Magnetic Parameters ◽  
Solar Eruptions ◽  
Very High

Context. Large-scale solar eruptions significantly affect space weather and damage space-based human infrastructures. It is necessary to predict large-scale solar eruptions; it will enable us to protect the vulnerable infrastructures of our modern society. Aims. We investigate the difference between flaring and nonflaring active regions. We also investigate whether it is possible to forecast a solar flare. Methods. We used photospheric vector magnetogram data from the Solar Dynamic Observatory’s Helioseismic Magnetic Imager to study the time evolution of photospheric magnetic parameters on the solar surface. We built a database of flaring and nonflaring active regions observed on the solar surface from 2010 to 2017. We trained a machine-learning algorithm with the time evolution of these active region parameters. Finally, we estimated the performance obtained from the machine-learning algorithm. Results. The strength of some magnetic parameters such as the total unsigned magnetic flux, the total unsigned magnetic helicity, the total unsigned vertical current, and the total photospheric magnetic energy density in flaring active regions are much higher than those of the non-flaring regions. These magnetic parameters in a flaring active region evolve fast and are complex. We are able to obtain a good forecasting capability with a relatively high value of true skill statistic. We also find that time evolution of the total unsigned magnetic helicity and the total unsigned magnetic flux provides a very high ability of distinguishing flaring and nonflaring active regions. Conclusions. We can distinguish a flaring active region from a nonflaring region with good accuracy. We confirm that there is no single common parameter that can distinguish all flaring active regions from the nonflaring regions. However, the time evolution of the top two magnetic parameters, the total unsigned magnetic flux and the total unsigned magnetic helicity, have a very high distinguishing capability.

scholarly journals Chronology of Formation of Solar Radio Burst Types III and V Associated with Solar Flare Phenomenon on 19th September 2011

2013 ◽  
Vol 24 ◽  
pp. 32-42
Author(s):  
Zety Sharizat Hamidi ◽  
N.N.M. Shariff
Keyword(s):  
Active Region ◽  
Solar Flare ◽  
Solar Radio ◽  
Active Regions ◽  
Radio Flux ◽  
X Ray ◽  
Type Iii ◽  
Solar Bursts ◽  
Type V

The formation of two different solar bursts, type III and V in one solar flare event is presented. Both bursts are found on 19th September 2011 associated with C-class flares on active region 1295. From the observation, we believed that the mechanism of evolution the bursts play an important role in the event. It is found that type V burst appeared in five minutes after type III. There are a few active regions on the solar disk but most are magnetically simple and have remained rather quiet. An interpretation of this new result depends critically on the number of sunspots and the role of active region 1295. Sunspot number is increased up to 144 with seven sunspots can be observed. During that event, the speed of solar wind exceeds 433.8 km/second with 2.0 g/cm3 density of protons in the solar corona. Currently, radio flux is also high up to 150 SFU. The solar flare type C6 is continuously being observed in the X-ray region for 24 hours since 1541 UT and a maximum C1 is detected on 1847 UT. Although the sources of both bursts are same, the direction and ejection explode differently. It is believed that the ejection of particles in a type III burst is higher than solar burst type V.

scholarly journals A Model of Solar X-ray Bright Points and Ephemeral Active Regions

1979 ◽  
Vol 32 (6) ◽  
pp. 671 ◽  
Author(s):  
JH Piddington
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Flux Rope ◽  
Active Regions ◽  
Activity Cycle ◽  
Solar Magnetic Fields ◽  
Flux Tubes ◽  
X Ray ◽  
Field System

Solar ephemeral active regions may provide a larger amount of emerging magnetic flux than the active regions themselves, and the origin and disposal of this flux pose problems. The related X-ray bright points are a major feature of coronal dynamics, and the two phenomena may entail a revision of our ideas of the activity cycle. A new large-scale subsurface magnetic field system has been suggested, but it is shown that such a system is neither plausible nor necessary. The emerging magnetic bipoles merely represent loops in pre-existing vertical flux tubes which are parts of active regions or the remnants of active regions. These loops result from the kink (or helical) instability in a twisted flux tube. Their observed properties are explained in terms of the flux-rope theory of solar fields. The model is extended to some dynamical effects in emerging loops. Further observations of ephemeral active regions may provide important tests between the traditional and flux-rope theories of solar magnetic fields.

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