TIME VARIATIONS OF THE CALCIUM ELEMENTAL ABUNDANCE IN FLARES FROM NOAA ACTIVE REGIONS 2562 AND 2779

1988 ◽  
Vol 49 (C1) ◽  
pp. C1-189-C1-193
Author(s):  
J. SYLWESTER ◽  
M.-C. ZOLCINSKI-COUET ◽  
R. D. BENTLEY ◽  
J. R. LEMEN
Keyword(s):  
Active Regions ◽  
Elemental Abundance ◽  
Time Variations

Time Variations of the Calcium Elemental Abundance in Flares from NOAA Active Regions 2562 and 2779

1988 ◽  
Vol 102 ◽  
pp. 189-193
Author(s):  
J. Sylwester ◽  
M.-C. Zolcinski-Couet ◽  
R.D. Bentley ◽  
J.R. Lemen
Keyword(s):  
Solar Maximum ◽  
Active Regions ◽  
Elemental Abundance ◽  
Crystal Spectrometer ◽  
Solar Maximum Mission ◽  
Bent Crystal ◽  
Time Variations ◽  
Abundance Variation ◽  
Future Work

AbstractAnalysis of flare spectra obtained with the Bent Crystal Spectrometer aboard the Solar Maximum Mission (SMM) satellite enables the determination of the fluxes in the resonance (w) line of Ca XIX and the near-by continuum. The line-to-continuum intensity ratio is a sensitive measure of the calcium elemental abundance (Aca) relative to hydrogen in the emitting plasma. In previous investigations we found the calcium abundance varies from flare to flare. In the present investigation we analyse the variations ofAcafor flares which occurred in two active regions well observed bySMM. We conclude that it is not possible to correlate the abundance variations with the time of the flare occurrence as suggested in an earlier paper for flares produced from a single active region. Further, we find no convincing correlation of abundance variation with any other flare characteristics. This negative result will stimulate future work on the physical interpretation of the calcium abundance variation.

scholarly journals Time Variations of Solar X-ray Bright Points

1975 ◽  
Vol 68 ◽  
pp. 23-24
Author(s):  
L. Golub ◽  
A. S. Krieger ◽  
J. K. Silk ◽  
A. F. Timothy ◽  
G. S. Vaiana
Keyword(s):  
Large Scale ◽  
Solar Surface ◽  
Active Regions ◽  
Lifetime Distribution ◽  
Comprehensive Review ◽  
X Ray ◽  
High Loop ◽  
Diffuse Cloud ◽  
Time Variations ◽  
Present Summary

SummaryAn example of the overall view of the X-ray corona (nominal filter passband 2–32 Å and 44–54 Å) showing a coronal hole, filament activity, bright points and the large scale-scale loop structures, is shown in Figure 1. This is one of the 32000 X-ray images obtained with the AS & E X-ray telescope on Skylab. A comprehensive review describing the characteristics of the various features and their implications regarding the high velocity solar streams, evolution of magnetic fields in active regions, and sources of soft X-ray emission has been given by Vaiana et al. (1975). In the present summary we will only be concerned with the bright points. Studies of solar X-ray bright points, show that these features represent a distinct class of solar activity. Bright points appear first as a diffuse cloud of soft X-ray emission typically growing to 30″ in diameter, with growth rates of ∼1 km s−1. Several hours after the point first becomes visible a bright compact core forms, growing to 10″. The lifetime distribution of bright points follows a Poisson distribution with a mean of eight hours (see references). The points are distributed uniformly over the entire solar surface, with approximately 500 on the Sun at any time. Their occurrrence appears to be independent of major active regions, except for a visibility factor near high loop structures or a possible decrease in number in active region latitudes.

Time Variations in Coronal Active Regions

1975 ◽  
pp. 103-103 ◽  
Author(s):  
A. S. Krieger ◽  
R. C. Chase ◽  
M. Gerassimenko ◽  
S. W. Kahler ◽  
A. F. Timothy ◽  
...  
Keyword(s):  
Active Regions ◽  
Time Variations

scholarly journals The HeI λ10830 Å Line as an Indicator of the Chromospheric and Coronal Activity of the Sun

1991 ◽  
Vol 130 ◽  
pp. 252-265
Author(s):  
A.G. Shcherbakov ◽  
Z.A. Shcherbakova
Keyword(s):  
Line Profile ◽  
Coronal Holes ◽  
Solar Limb ◽  
Active Regions ◽  
Solar Chromosphere ◽  
The Sun ◽  
K Index ◽  
Short Summary ◽  
Coronal Activity ◽  
Time Variations

AbstractThe behaviour of the HeI λ10830 Å line profile in spectra of solar features is reviewed. The connection of line characteristics with various phenomena on the solar disc, such as plages (faculae), sunspots, jets, prominences, coronal holes, flares, fine structure and emission above the solar limb, is discussed. We present a short summary of the mechanisms for helium excitation in the solar chromosphere. Time variations of the line profile, observed in quiet and active regions, and HeI λ10830 Å absorption in the Sun as a star are discussed and compared with other indexes of solar activity. It is shown that the equivalent width of the helium line varies in an 11 year cycle and reflects the 27 day periodicity of the rotation of the Sun. It is also shown that the HeI line is a more sensitive index of activity than K-index.

scholarly journals Signature and escape of highly fractionated plasma in an active region

2021 ◽  
Vol 508 (2) ◽  
pp. 1831-1841
Author(s):  
David H Brooks ◽  
Stephanie L Yardley
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Active Region ◽  
Active Regions ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Composition Analysis ◽  
Closed Field ◽  
Coronal Loops ◽  
Magnetic Field Model

ABSTRACT Accurate forecasting of space weather requires knowledge of the source regions where solar energetic particles (SEP) and eruptive events originate. Recent work has linked several major SEP events in 2014, January, to specific features in the host active region (AR 11944). In particular, plasma composition measurements in and around the footpoints of hot, coronal loops in the core of the active region were able to explain the values later measured in situ by the Wind spacecraft. Due to important differences in elemental composition between SEPs and the solar wind, the magnitude of the Si/S elemental abundance ratio emerged as a key diagnostic of SEP seed population and solar wind source locations. We seek to understand if the results are typical of other active regions, even if they are not solar wind sources or SEP productive. In this paper, we use a novel composition analysis technique, together with an evolutionary magnetic field model, in a new approach to investigate a typical solar active region (AR 11150), and identify the locations of highly fractionated (high Si/S abundance ratio) plasma. Material confined near the footpoints of coronal loops, as in AR 11944, that in this case have expanded to the AR periphery, show the signature, and can be released from magnetic field opened by reconnection at the AR boundary. Since the fundamental characteristics of closed field loops being opened at the AR boundary is typical of active regions, this process is likely to be general.

scholarly journals Time Variations in Coronal Active Regions

1975 ◽  
Vol 68 ◽  
pp. 103-103
Author(s):  
A. S. Krieger ◽  
R. C. Chase ◽  
M. Gerassimenko ◽  
S. W. Kahler ◽  
A. F. Timothy ◽  
...  
Keyword(s):  
Active Region ◽  
Potential Field ◽  
Active Regions ◽  
Field Approximation ◽  
X Ray ◽  
Evolutionary Changes ◽  
Potential Component ◽  
Time Variations ◽  
Field Lines

SummaryThe AS&E X-ray telescope experiment on Skylab has obtained images of the solar X-ray corona with a variety of time resolutions ranging from 21/2 s to the regular 12 ± 2 h synoptic observation rate. The form and brightness of coronal active region structures are seen to vary on time scales ranging from seconds, for flare associated changes, to several solar rotations for long term evolution of the regions. The extrapolation of photospheric magnetic fields into the corona, using the potential field approximation, results in a good morphological agreement between the form of the computed coronal field lines and the structure of many of the active regions observed. Thus, in general, the coronal active region structures follow potential field lines and the long term evolutionary changes can be explained on the basis of the spreading of the fields. Short term changes in active region structure frequently take the form of selective brightening or dimming of pre-existing loops due to changes in the pressure of the emitting coronal plasma. In these cases, variations in the non-potential component of the coronal fields supporting and containing the plasma are implied.

scholarly journals Solar Activity Observed in X-Rays and the EUV from OSO 7

1975 ◽  
Vol 68 ◽  
pp. 25-42 ◽  
Author(s):  
Roger J. Thomas
Keyword(s):  
Active Regions ◽  
Impulsive Phase ◽  
Magnetic Polarity ◽  
X Rays ◽  
Active Centers ◽  
X Ray ◽  
Component Type ◽  
Wide Range ◽  
Time Variations ◽  
Continuous Injection

Since 1971 the Goddard X-ray and EUV spectroheliograph aboard OSO 7 has been measuring the spatial distribution and time-variations of localized temperature and density features in solar active centers and flares. In some cases the sizes, shapes, orientations and locations of emitting plasmas at temperatures ranging from 104 K (Hα) to as high as 2 × 107 K (Fe xxv) have now been measured simultaneously. Our observations of active regions are consistent with the coronal structure being made up of nested systems of arches with footpoints in areas of opposite magnetic polarity. Temperatures seem to increase for arches nearer the center and also towards the top of any given magnetic arch, the innermost loops having the highest temperature gradients. There is also some evidence for electric current flow along such loops. Radiative cooling is significant for the region's hot central core which therefore must be maintained by a more or less continuous injection of energy.A nested arch structure is also indicated for XUV flares of the two-component type, which likewise may require continuous energy input since conduction cooling should otherwise be very rapid. Multiple spikes during the impulsive phase seem to represent the consecutive triggering of different sources within the region and may occur outside of any detectable pre-existing coronal feature. Comparison of spatial distributions at several wavelengths during various stages of flare events provides information on interactions between the wide range of atmospheric levels involved. We have evidence for polarization of about 20% in a number of X-ray bursts, continuing throughout the decay phase. At least for some flares, our measurements seem to contradict the model of electron beams being radially injected into the chromosphere.

Synoptic Charts of the Solar Eclipses of 1990 and 1991

1994 ◽  
Vol 144 ◽  
pp. 517-521
Author(s):  
Z. Mouradian ◽  
G. Buchholtz ◽  
G. Zlicaric
Keyword(s):  
Solar Limb ◽  
Active Regions ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractThe synoptic charts of solar rotations 1831 and 1844 have been drawn up, corresponding to the eclipses of 22 July 1990 and 11 July 1991. These charts contain the active regions and the filaments, and show the position of the solar limb, at the time of the eclipse. They are for use in studying the coronal structures observed during these eclipses. The variation of these structures is given in the table. The last section of the article contains a formula for identifying the structures out of the limb.

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