scholarly journals Low Brightness Temperature in Microwaves at Periphery of Some Solar Active Regions

2017 ◽  
Vol 54 (3) ◽  
pp. 58-67
Author(s):  
B. I. Ryabov ◽  
D. A. Bezrukov ◽  
J. Kallunki
Keyword(s):  
Brightness Temperature ◽  
Open Field ◽  
Active Regions ◽  
Source Surface ◽  
The Sun ◽  
Coronal Emission ◽  
Field Source ◽  
Wavelet Space ◽  
Solar Active Regions ◽  
Field Lines

AbstractThe microwave regions with low brightness temperature are found to overlap the regions of the depressed coronal emission and open field lines at the periphery of two solar active regions (ARs). The imaging microwave observations of the Sun with the Nobeyama Radio heliograph at 1.76 cm, the MRO-14 radio telescope of Metsähovi Radio Observatory at 0.8 cm, and the RT-32 of Ventspils International Radio Astronomy Centre in the range 3.2-4.7 cm are used. To reduce the noise in the intensity distribution of the RT-32 maps of the Sun, one wavelet plane of “à trous” wavelet space decomposition is subtracted from each map. To locate the open-field regions, the full-Sun coronal magnetic fields with the potential field source surface (PFSS) model for RSS= 1.8 Rʘare simulated. We conclude that the revealed LTRs present narrow coronal hole-like regions near two ARs and imply an extra investigation on the plasma outflow.

scholarly journals Evidence for Open Field Lines from Active Regions: Short Communication

1980 ◽  
Vol 91 ◽  
pp. 261-261
Author(s):  
K. V. Sheridan
Keyword(s):  
Open Field ◽  
Subject Matter ◽  
Short Communication ◽  
Active Regions ◽  
Theoretical Physics ◽  
University Of Colorado ◽  
Solar Active Regions ◽  
The Subject ◽  
Field Lines ◽  
Sydney Australia

A paper that has considerable relevance of the subject matter of this symposium is the following: “Evidence for Extreme Divergence of Open Field Lines from Solar Active Regions,” by G. A. Dulk (Division of Radiophysics, CSIRO, Sydney, Australia and Department of Astro-Geophysics, University of Colorado, Boulder, Colorado), D. B. Melrose (Department of Theoretical Physics, University of Sydney, Australia) and S. Suzuki (Division of Radiophysics, CSIRO, Sydney, Australia).

Evidence for Extreme Divergence of Open Field Lines from Solar Active Regions

1979 ◽  
Vol 3 (6) ◽  
pp. 375-379 ◽  
Author(s):  
G. A. Dulk ◽  
D. B. Melrose ◽  
S. Suzuki
Keyword(s):  
Magnetic Field ◽  
Open Field ◽  
Interplanetary Space ◽  
Active Regions ◽  
Type Iii ◽  
Solar Active Regions ◽  
Field Lines ◽  
Type V ◽  
Open Magnetic Field

In this paper we review the evidence on the structure of the open magnetic field lines that emerge from solar active regions into interplanetary space. The evidence comes mainly from the measured sizes, positions and polarization of Type III and Type V bursts, and from electron streams observed from space. We find that the observations are best interpreted in terms of a strongly-diverging field topology, with the open field lines filling a cone of angle ~60°.

scholarly journals Depressed Emission between Magnetic Arcades near a Sunspot

2016 ◽  
Vol 25 (2) ◽  
Author(s):  
B. I. Ryabov ◽  
K. Shibasaki
Keyword(s):  
Active Region ◽  
Open Field ◽  
Potential Field ◽  
Source Surface ◽  
The Sun ◽  
X Rays ◽  
Field Source

AbstractThe locations of the depressed emission in microwaves, EUV and soft X-rays are compared with each other and with the location of the plasma outflow in the active region (AR) 8535 on the Sun. We found that two open-field regions overlap the regions of depressed emission near the AR's sunspot. These two open-field regions are simulated with the potential-field source-surface (PFSS) model under radial distances of

Source-dependent properties of the background slow solar wind encountered by Parker Solar Probe

2021 ◽  
Author(s):  
Léa Griton ◽  
Sarah Watson ◽  
Nicolas Poirier ◽  
Alexis Rouillard ◽  
Karine Issautier ◽  
...  
Keyword(s):  
Solar Wind ◽  
Extreme Ultraviolet ◽  
Plasma Heating ◽  
Coronal Holes ◽  
Slow Solar Wind ◽  
Source Surface ◽  
Field Source ◽  
Flux Tubes ◽  
Field Lines

<p>Different states of the slow solar wind are identified from in-situ measurements by Parker Solar Probe (PSP) inside 50 solar radii from the Sun (Encounters 1, 2, 4, 5 and 6). At such distances the wind measured at PSP has not yet undergone significant transformation related to the expansion and propagation of the wind. We focus in this study on the properties of the quiet solar wind with no magnetic switchbacks. The Slow Solar Wind (SSW) states differ by their density, flux, plasma beta and magnetic pressure. PSP's magnetic connectivity established with Potential Field Source Surface (PFSS) reconstructions, tested against extreme ultraviolet (EUV) and white-light imaging, reveals the different states under study generally correspond to transitions from streamers to equatorial coronal holes. Solar wind simulations run along these differing flux tubes reproduce the slower and denser wind measured in the streamer and the more tenuous wind measured in the coronal hole. Plasma heating is more intense at the base of the streamer field lines rooted near the boundary of the equatorial hole than those rooted closer to the center of the hole. This results in a higher wind flux driven inside the streamer than deeper inside the equatorial hole. </p>

scholarly journals Solar active regions in Mg II light

1968 ◽  
Vol 35 ◽  
pp. 299-303
Author(s):  
Kerstin Fredga
Keyword(s):  
Active Regions ◽  
The Sun ◽  
Reversal Effect ◽  
Negative Results ◽  
Important Observation ◽  
Solar Active Regions

During 1965 two rockets were launched in order to obtain monochromatic pictures of the Sun in the Mg II line at 2802·7 Å. The Mg II filterheliograms have been compared with simultaneous Hα and Ca II K spectroheliograms. An important observation from both flights concerns the relative intensities of different active regions. In the Hα pictures there are old fairly faint active regions and newly formed more intense regions. In the Mg II pictures, however, the older regions appear more intense than the younger regions.Different explanations for this intensity-reversal effect have been considered. The effect has also been looked for in broadband Ca II H filterheliograms, with negative results, however.

scholarly journals Coronal magnetic fields from the inversion of linear polarization measurements

2009 ◽  
Vol 5 (S264) ◽  
pp. 96-98
Author(s):  
Yu Liu ◽  
Haosheng Lin ◽  
Jeff Kuhn
Keyword(s):  
Linear Polarization ◽  
Spatial Relation ◽  
Coronal Magnetic Field ◽  
Surface Model ◽  
Source Surface ◽  
Coronal Emission ◽  
Field Source ◽  
Close Relationship ◽  
The Difference ◽  
Ir Emission

AbstractReal 3-D coronal magnetic field reconstruction is expected to be made based on the technologies of IR spectrometry and tomography, in which the data from other wavelengths can be used as critical reference. Our recent studies focused on this issue are briefly reviewed in this paper. Liu & Lin (2008) first evaluated the validity of potential field source surface model applied to one of five limb regions in the corona by comparing the theoretical polarization maps with SOLARC observations in the IR Fe XIII 10747 Å forbidden coronal emission line (CEL). The five limb coronal regions were then studied together in order to study the spatial relation between the bright EUV features on the solar disk and the inferred IR emission sources, which were obtained from the inversion of the SOLARC linear polarization (LP) measurements (Liu 2009). The inversion for each fiber data in the field of view was made by finding the best location where the difference between the synthesized and the observed polarizations reaches the minimum in the integration path along the line of sight. We found a close relationship between the inferred IR emission source locations and the EUV strong emission positions.

scholarly journals Extreme ultraviolet observations of active regions in the solar corona

1968 ◽  
Vol 35 ◽  
pp. 395-402
Author(s):  
W. M. Burton
Keyword(s):  
High Temperature ◽  
Extreme Ultraviolet ◽  
Active Regions ◽  
Pinhole Camera ◽  
Emission Region ◽  
The Sun ◽  
Coronal Emission ◽  
Improved Design ◽  
Ultraviolet Observations ◽  
Plane Diffraction

The coronal features associated with solar active regions can be observed by recording images of the Sun at extreme ultraviolet (XUV) wavelengths. Pinhole cameras have been flown on stabilized sun-pointing ‘Skylark’ rockets to obtain broad-waveband XUV solar images. These images show localised emission from high-temperature regions located in the corona above calcium-plage areas. An improved design of pinhole camera, which uses a plane-diffraction grating to give increased spectral resolution, has recorded spectroheliograms in several intense solar lines including He II (304 Å), Fe IX–XI (180 Å), and Si X–XII (50 Å). Estimates are made of the size and brightness of the coronal emission region associated with a developing calcium-plage area.

Characterizing the Dynamics of CME-Driven Coronal Bright Fronts Using The SPREAdFAST Framework 

2021 ◽  
Author(s):  
Mohamed Nedal ◽  
Kamen Kozarev ◽  
Rositsa Miteva
Keyword(s):  
Energetic Particle ◽  
Large Scale ◽  
Numerical Models ◽  
Solar Energetic Particle ◽  
Time Dependent ◽  
Radiation Environment ◽  
Source Surface ◽  
The Sun ◽  
Particle Radiation ◽  
Field Source

<p>In this work, we present a full characterization of over 50 historical Coronal Mass Ejection (CME)-driven compressive waves in the low solar corona, related to solar energetic particle events near Earth, using the Solar Particle Radiation Environment Analysis and Forecasting - Acceleration and Scattering Transport (SPREAdFAST) framework. SPREAdFAST is a physics-based, operational heliospheric solar energetic particle (SEP) forecasting system, which incorporates a chain of data-driven analytic and numerical models for estimating: a) coronal magnetic field from Potential Field Source Surface (PFSS) and Magnetohydrodynamics (MHD); b) dynamics of large-scale coronal (CME-driven) shock waves; c) energetic particle acceleration; d) scatter-based, time-dependent SEP propagation in the heliosphere to specific time-dependent positions. SPREAdFAST allows for producing predictions of SEP fluxes at multiple locations in the inner heliosphere, by modeling their acceleration at CMEs near the Sun, and their subsequent interplanetary transport. We used sequences of base-difference images obtained from the AIA instrument on board the SDO satellite, with 24-second cadence. We calculated time-dependent speeds in both the radial and lateral (parallel to the solar limb) directions, mean intensities and thicknesses of the fronts, and major and minor axes. This is essential for characterizing the SEP spectra near the Sun. The kinematics measurements were used to generate time-dependent 3D geometric models of the wave fronts and time-dependent plasma diagnostics using MHD and DEM model results.</p><p> </p><p> </p>

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