Probability density of irradiance for Electromagnetic waves propagating through the solar corona

2021 ◽  
Author(s):  
Yousef Mostafa Shishter
Keyword(s):  
Solar Corona ◽  
Probability Density ◽  
Electromagnetic Waves

Imaging the Solar Corona during the 2015 March 20 Eclipse using LOFAR

2020 ◽  
Author(s):  
Aoife Maria Ryan ◽  
Peter T. Gallagher ◽  
Eoin P. Carley ◽  
Diana E. Morosan ◽  
Michiel A. Brentjens ◽  
...  
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
Electromagnetic Waves ◽  
High Spatial Resolution ◽  
Low Frequency ◽  
Angular Width ◽  
Interferometric Imaging ◽  
Low Frequencies ◽  
Point Spread ◽  
Spread Function

<p>The solar corona is a highly-structured plasma which reaches temperatures of more than ~2MK. At low radio frequencies (≤ 400 MHz), scattering and refraction of electromagnetic waves are thought to broaden sources to several arcminutes. However, exactly how source size relates to scattering due to turbulence is still subject to investigation. This is mainly due to the lack of high spatial resolution observations of the solar corona at low frequencies. Here, we use the LOw Frequency ARray (LOFAR) to observe the solar corona at 120-180 MHz using baselines of up to ~3.5 km (~1--2’) during a partial solar eclipse of 2015 March 20. We use a lunar de-occultation technique to achieve higher spatial resolution than that attainable via traditional interferometric imaging. This provides a means of studying source sizes in the corona that are smaller than the angular width of the interferometric point spread function. </p>

scholarly journals LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse

2021 ◽  
Author(s):  
Aoife Maria Ryan ◽  
Peter T. Gallagher ◽  
Eoin P. Carley ◽  
Michiel A. Brentjens ◽  
Pearse C. Murphy ◽  
...  
Keyword(s):  
Solar Corona ◽  
Spatial Resolution ◽  
Solar Eclipse ◽  
Electromagnetic Waves ◽  
Imaging Techniques ◽  
Active Regions ◽  
Density Fluctuations ◽  
Source Size ◽  
Interferometric Imaging ◽  
Low Frequencies

<p>The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.</p><p><br><br></p>

scholarly journals PIC Simulations of Excited Waves in the Plasmoid Instability

2022 ◽  
Vol 8 ◽  
Author(s):  
Mahdi Shahraki Pour ◽  
Mahboub Hosseinpour
Keyword(s):  
Particle Acceleration ◽  
Kinetic Energy ◽  
Solar Corona ◽  
Current Sheet ◽  
Electromagnetic Waves ◽  
Magnetic Energy ◽  
Particle In Cell ◽  
Guide Field ◽  
Collisionless Regime ◽  
Accelerated Particles

Fragmentation of an elongated current sheet into many reconnection X-points, and therefore multiple plasmoids, occurs frequently in the solar corona. This speeds up the release of solar magnetic energy in the form of thermal and kinetic energy. Moreover, due to the presence of multiple reconnection X-points, the particle acceleration is more efficient in terms of the number of accelerated particles. This type of instability called “plasmoid instability” is accompanied with the excitation of some electrostatic/electromagnetic waves. We carried out 2D particle-in-cell simulations of this instability in the collisionless regime, with the presence of non-uniform magnetic guide field to investigate the nature of excited waves. It is shown that the nature and properties of waves excited inside and outside the current sheet are different. While the outside perturbations are transient, the inside ones are long-lived, and are directly affected by the plasmoid instability process.

scholarly journals On the Propagation of the Electrons Related to Type III Bursts

1980 ◽  
Vol 86 ◽  
pp. 327-327 ◽  
Author(s):  
G.V. de Genouillac ◽  
D.F. Escande
Keyword(s):  
Solar Corona ◽  
Electromagnetic Waves ◽  
Solar Radio ◽  
Interplanetary Medium ◽  
Electron Plasma ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
Plasma Oscillations ◽  
Type Iii ◽  
Electron Clouds

Type III solar radio bursts are known to be excited by solar electron clouds travelling outwards through the solar corona and interplanetary medium. According to the “plasma hypothesis”, electron plasma oscillations are created by the passing beam, which are in turn converted into electromagnetic waves.

Coherent emission driven by energetic ring-beam electrons in the solar corona

2020 ◽  
Author(s):  
Xiaowei Zhou ◽  
Patricio Munoz Sepulveda ◽  
Joerg Buechner ◽  
Siming Liu
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Electromagnetic Waves ◽  
Density Ratio ◽  
Electron Cyclotron ◽  
Polarization Degree ◽  
Magnetized Plasmas ◽  
Electrostatic Waves ◽  
Beam Electron ◽  
Ring Shape

<p>We analyzed properties of waves excited by mildly relativistic electron beams propagating along magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser (ECM) instabilities driven by the positive momentum gradient of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5-dimensional fully kinetic particle-in-cell (PIC) simulations were carried out.</p><p>To quantify excited wave properties in different coronal conditions, we investigated the dependence of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency <em>ω<sub>ce</sub></em> is lower than the electron plasma frequency <em>ω<sub>pe</sub></em>, it is difficult to produce escaping electromagnetic waves with frequency <em>ω > ω<sub>pe </sub></em>and small refractive index <em>ck</em>/<em>ω</em> <em>< 1</em> (<em>k</em> and <em>c</em> are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with <em>ω<sub>ce</sub>/ω<sub>pe </sub>≥ 1</em>. The anisotropy of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.</p>

Colour Photometry of the Solar Corona of July 11, 1991

1994 ◽  
Vol 144 ◽  
pp. 597-599 ◽  
Author(s):  
I. V. Alexeyeva ◽  
N. L. Kroussanova ◽  
M. V. Streltsova
Keyword(s):  
Solar Corona ◽  
Red Emission ◽  
Coronal Structures

AbstractThe results of photometry of colour positives of the solar corona of July 11, 1991 are presented. Observations of the white corona were made without radial niters in Jojutla (Mexico). Dependences of coronal brightness on distance in the red (640 nm) and blue (420 nm) wavelength intervals are deduced for different coronal structures up to 3.0-3.5R⊙. The effect of ”reddening“ is noted. The excess of the red emission to the blue one (I640nm/I420nm) is found to be 1.20 and 1.17 at distance of 2.2R⊙for the N-E helmet streamer (P ≃ 37°) and the N-W region of low brightness (P ≃ 339°), respectively.

July 11, 1991 Eclipse Corona Photometry by the Results of Electropolarimetric and CCD-Matrix Observations

1994 ◽  
Vol 144 ◽  
pp. 567-569
Author(s):  
V. Kulidzanishvili ◽  
D. Georgobiani
Keyword(s):  
Solar Corona ◽  
Observational Data ◽  
Solar Limb ◽  
Ccd Matrix

AbstractThe observational data of July 11, 1991 eclipse solar corona obtained by both electropolarimeter (EP) and CCD-matrix were processed. Using these data, the solar corona photometry was carried out. The results of EP data are compared with the ones of CCD data. It must be noted here that the CCD data give us only characteristics of the inner corona, while the EP data show the features of both the inner and middle corona up to 4R⊙. Standard flattening indexϵis evaluated from both data. The dependence of the flattening index on the distance from the solar limb is investigated. The isophotes in Na and Ca lines are plotted. Based on these data some ideas and conclusions on the type of the solar corona are presented.

Sign in / Sign up

Export Citation Format

Share Document