Angular scattering of radio waves: Implications for mode coupling in the solar corona

1995 ◽  
Vol 439 ◽  
pp. 494 ◽  
Author(s):  
T. S. Bastian
Keyword(s):  
Solar Corona ◽  
Mode Coupling ◽  
Radio Waves ◽  
Angular Scattering

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

scholarly journals 58. Results of observations of the scattering of radio waves by the electronic inhomogeneities of the solar corona

1957 ◽  
Vol 4 ◽  
pp. 313-317
Author(s):  
V. V. Vitkevitch
Keyword(s):  
Solar Corona ◽  
Radio Source ◽  
Crab Nebula ◽  
New Method ◽  
Radio Waves ◽  
The Crab Nebula

A new method for the investigation of the solar corona, suggested by us (Vitkevitch, 1951) [1], consists of observing the radio source identified with the Crab nebula (NGC 1952; α = 05h 31m 40s, δ = 22° 10′) when it is covered by the solar corona. This occurs every year on 14–15 June.

Observations of mode coupling in the solar corona and bipolar noise storms

Solar Physics ◽  
1992 ◽  
Vol 138 (1) ◽  
pp. 163-187 ◽  
Author(s):  
S. M. White ◽  
G. Thejappa ◽  
M. R. Kundu
Keyword(s):  
Solar Corona ◽  
Mode Coupling

scholarly journals Mode Coupling in the Solar Corona. V. Reduction of the Coupled Equations

1977 ◽  
Vol 30 (6) ◽  
pp. 661 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Solar Corona ◽  
Mode Coupling ◽  
Mhd Waves ◽  
Fast Mode ◽  
Coupling Theory ◽  
Mode Coupling Theory ◽  
Coupled Equations

A simplified version of the mode-coupling theory of Clemmow and Heading is developed by reducing the set of coupled equations to two for the magnetoionic theory and three for the MHD theory. The simplified theory reproduces known results for coupling in the neighbourhood of coupling points. It is used to treat coupling between the MHD waves, and it is found that coupling between the fast mode and the Alfven mode for VA ;?; C, is stronger than the coupling between any other pair of modes. The strongest coupling of all is between the Alfven and slow (magnetoacoustic) modes for VA ~ C,.

scholarly journals Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves

1997 ◽  
Vol 15 (4) ◽  
pp. 387-396 ◽  
Author(s):  
C. Lacombe ◽  
J.-L. Steinberg ◽  
C. C. Harvey ◽  
D. Hubert ◽  
A. Mangeney ◽  
...  
Keyword(s):  
Spectral Power ◽  
Local Density ◽  
Thin Sheet ◽  
Power Laws ◽  
Density Fluctuations ◽  
Scattering Coefficient ◽  
Radio Waves ◽  
Angular Scattering ◽  
Propagation Experiment ◽  
First Time

Abstract. Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth's magnetosheath, the ISEE 1-2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5 – 4 × 10–9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to1RE) just downstream of the shock ramp, and close to the magnetopause.

Quasi-harmonic faraday-rotation fluctuations of radio waves when sounding the outer solar corona

2000 ◽  
Vol 26 (8) ◽  
pp. 544-552 ◽  
Author(s):  
A. I. Efimov ◽  
L. N. Samoznaev ◽  
V. E. Andreev ◽  
I. V. Chashei ◽  
M. K. Bird
Keyword(s):  
Solar Corona ◽  
Faraday Rotation ◽  
Radio Waves

scholarly journals Mode Coupling in the Solar Corona. IV. Magnetohydrodynamic Waves

1977 ◽  
Vol 30 (6) ◽  
pp. 647 ◽  
Author(s):  
DB Melrose ◽  
MA Simpson
Keyword(s):  
General Theory ◽  
Solar Corona ◽  
Mode Coupling ◽  
Stratified Medium ◽  
Mhd Waves ◽  
Fast Mode ◽  
Slow Mode ◽  
Magnetohydrodynamic Waves ◽  
Quartic Equation ◽  
Obliquely Incident

A general theory for coupling between MHD waves obliquely incident on a stratified medium is developed. Coupling between the Alfvtln mode and the magnetoacoustic mode (the fast mode for VA > cs and the slow mode for VA < cs) is affected little by the finiteness of Cs/VA for VA >> Cs and the coupling becomes weaker as Cs/VA is increased towards unity. Coupling between the fast and slow modes for VA ≈ C. is discussed qualitatively using solutions of the MHD counterpart of the Booker quartic equation.

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