scholarly journals Very Large Array (VLA) Observations of Solar Active Regions

1980 ◽  
Vol 86 ◽  
pp. 109-117
Author(s):  
Kenneth R. Lang ◽  
Robert F. Willson
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Circular Polarization ◽  
Zeeman Effect ◽  
Active Regions ◽  
Large Array ◽  
Magnetic Dipoles ◽  
Very Large Array ◽  
Magnetic Structures ◽  
Brightness Temperatures

Very Large Array (VLA) synthesis maps of the total intensity and the circular polarization of three active regions at 6 cm wavelength are presented. The radiation from each active region is dominated by a few intense cores with angular sizes of ~ 0.5′, brightness temperatures of ~ 106 K, and degrees of circular polarization of 30 to 90%. Some of the core sources within a given active region exhibit opposite senses of circular polarization, suggesting the feet of magnetic dipoles, and the high brightness temperatures suggest that these magnetic structures belong to the low solar corona. We also present comparisons between our VLA maps of circular polarization and Zeeman effect magnetograms of the lower lying photosphere. There is an excellent correlation between the magnetic structures inferred by the two methods, indicating that synthesis maps of circular polarization at 6 cm can be used to delineate magnetic structures in the low solar corona.

Very Large Array Observations of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 195-199
Author(s):  
K. R. Lang
Keyword(s):  
High Resolution ◽  
Active Region ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Coronal Loops ◽  
Large Array ◽  
Very Large Array ◽  
Magnetically Trapped ◽  
High Magnetic Field Strength

AbstractVery Large Array (VLA) observations indicate that electrons accelerated in one active region can travel along otherwise-invisible, large-scale coronal loops to trigger flares in another widely-separated active region, as well as from the magnetic loops connecting them. The VLA provides high-resolution, full-disk images of quiescent, or non-flaring, coronal loops within individual active regions (at 20 cm) and between or beyond them (at 90 cm). Both ground-based radio telescopes and spaceborne X-ray telescopes provide high-resolution images of the ubiquitous coronal loops whose hot, dense magnetically-trapped plasma emits thermal bremsstrahlung. Radio observations can be used to specify the strength and structure of the magnetic fields in the low solar corona. We find a high magnetic field strength in the million-degree plasma above large sunspots – 75 to 80 percent of the value in the underlying photospheric sunspots; as well as coronal regions of non-potential, current-amplified magnetic fields. Some long-lasting (hours) coronal radio sources found on the Sun and other active stars require nonthermal radiation and nearly continuous acceleration of energetic electrons.

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.

Structure of a solar active region from RATAN 600 and very large array observations

1986 ◽  
Vol 301 ◽  
pp. 460 ◽  
Author(s):  
Sh. B. Akhmedow ◽  
V. N. Borovik ◽  
G. B. Gelfreikh ◽  
V. M. Bogod ◽  
A. N. Korzhavin ◽  
...  
Keyword(s):  
Active Region ◽  
Solar Active Region ◽  
Large Array ◽  
Very Large Array

scholarly journals FIP Effect and FIP-Dependent Bias in the Solar Corona

2004 ◽  
Vol 219 ◽  
pp. 493-497
Author(s):  
B.N. Dwivedi ◽  
A. Mohan ◽  
E. Landi
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Solar Disk ◽  
Field Of View ◽  
Magnetic Structures ◽  
Abundance Anomalies ◽  
Soho Spacecraft

Using EUV spectra of an active region observed off the solar disk by the SOHO/SUMER spectrograph on the SOHO spacecraft, we investigate the dependence of the FIP effect on the height above the photosphere, and its relation to plasma magnetic structures present in the field of view. We also investigate the possibility of the FIP bias in the low-FIP elements to be FIP-dependent, so that different abundance anomalies must be found even within the low-FIP class of elements, which can provide important constraints on the FIP effect models.

scholarly journals The Evolution of Unstable 'Beta-Gamma' Magnetic Fields of Active Region AR 2222

2015 ◽  
Vol 48 ◽  
pp. 95-102
Author(s):  
Zety Sharizat Hamidi ◽  
S.N.U. Sabri ◽  
N.N.M. Shariff ◽  
C. Monstein
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Solar Flares ◽  
Active Regions ◽  
Group Type ◽  
Solar Burst ◽  
Type Iv ◽  
Fine Structures ◽  
Using Data

This event allows us to investigate how plasma–magnetic field interactions in the solar corona can produce suprathermal electron populations over periods from tens of minutes to several hours, and the interactions of wave-particle and wave-wave lead to characteristic fine structures of the emission. An intense and broad solar radio burst type IV was recorded by CALLISTO spectrometer from 240-360 MHz. Using data from a the KRIM observatory, we aim to provide a comprehensive description of the synopsis formation and dynamics of a a single solar burst type IV event due to active region AR2222. For five minutes, the event exhibited strong pulsations on various time scales and “broad patterns” with a formation of a group type III solar burst. AR 2222 remained the most active region, producing a number of minor C-Class solar flares. The speed of the solar wind also exceeds 370.8 km/second with 10.2 g/cm3 density of proton in the solar corona. The radio flux also shows 171 SFU. Besides, there are 3 active regions, AR2217, AR2219 and AR2222 potentially pose a threat for M-class solar flares. Active region AR2222 have unstable 'beta-gamma' magnetic fields that harbor energy for M-class flares. As a conclusion, we believed that Sun’s activities more active in order to achieve solar maximum cycle at the end of 2014.

scholarly journals The Sun at the VLA's Metric and Decimetric Wavelengths

1990 ◽  
Vol 142 ◽  
pp. 523-524
Author(s):  
S. M. White ◽  
M. R. Kundu ◽  
N. Gopalswamy ◽  
E. J. Schmahl
Keyword(s):  
Large Scale ◽  
Dynamic Range ◽  
Active Regions ◽  
High Dynamic Range ◽  
The Sun ◽  
Large Array ◽  
Very Large Array ◽  
Preliminary Results ◽  
High Dynamic ◽  
Coronal Structures

During September 1988 (International Solar Month) we observed the Sun with the Very Large Array on 4 days in the period Sep. 11-17. The VLA was in its most compact configuration, which is ideal for studying large-scale coronal structures. Here we summarize some preliminary results of the observations at 0.333 and 1.5 GHz. Despite the presence of numerous active regions the Sun was actually very quiet, with no flares during our observing, and this allowed us to make high-dynamic-range maps.

scholarly journals Observations of Solar Active Regions at 2 and 6 cm Wavelengths with 3 Arc Second Resolution

1980 ◽  
Vol 86 ◽  
pp. 105-108
Author(s):  
T. Velusamy ◽  
M. R. Kundu
Keyword(s):  
Fine Structure ◽  
Active Regions ◽  
Field Of View ◽  
Large Array ◽  
The West ◽  
Very Large Array ◽  
Group I ◽  
West Limb ◽  
Solar Active Regions ◽  
Sunspot Groups

We have used the Very Large Array of the NRAO to observe solar active regions at 2 and 6 cm wavelengths in May 1979. In this paper we present and discuss the fine structure components of a sunspot associated radio region observed with a resolution of 3″ arc on May 4 and 5, 1979. In this region (McMath 15974) there were two distinct groups of sunspots separated by about 3′ arc. Group I located towards the west limb contained two spots while Group II in the east was a complex containing several spots that emerged during the period of our observations. At 6 cm both the sunspot groups were within the primary beam whereas at 2 cm only Group I was within the field of view. The VLA observations were made at 6 and 2 cm alternating between them every 5 minuts. The region was mapped with a resolution of about 3″ x 3″ using 10 hours of synthesis data on each day.

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