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Title: EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS

Abstract

Simultaneous observations of solar type III radio bursts obtained by the STEREO A, B, and WIND spacecraft at low frequencies from different vantage points in the ecliptic plane are used to determine their directivity. The heliolongitudes of the sources of these bursts, estimated at different frequencies by assuming that they are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere, and the heliolongitudes of the spacecraft are used to estimate the viewing angle, which is the angle between the direction of the magnetic field at the source and the line connecting the source to the spacecraft. The normalized peak intensities at each spacecraft R{sub j} = I{sub j} /{Sigma}I{sub j} (the subscript j corresponds to the spacecraft STEREO A, B, and WIND), which are defined as the directivity factors are determined using the time profiles of the type III bursts. It is shown that the distribution of the viewing angles divides the type III bursts into: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field with angular width of {approx}2 Degree-Sign and (2) bursts emitting into a wider cone with angular widthmore » spanning from {approx} - 100 Degree-Sign to {approx}100 Degree-Sign . The plots of the directivity factors versus the viewing angles of the sources from all three spacecraft indicate that the type III emissions are very intense along the tangent to the spiral magnetic field lines at the source, and steadily fall as the viewing angles increase to higher values. The comparison of these emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.« less

Authors:
;  [1]
  1. Astronomy Department, University of Maryland, College Park, MD 20742 (United States)
Publication Date:
OSTI Identifier:
22011706
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 745; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; MAGNETIC FIELDS; MASS; SOLAR ATMOSPHERE; SUN

Citation Formats

Thejappa, G, Bergamo, M, and MacDowall, R. J., E-mail: thejappa.golla@nasa.gov, E-mail: mbergamo@umd.edu, E-mail: Robert.MacDowall@nasa.gov. EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS. United States: N. p., 2012. Web. doi:10.1088/0004-637X/745/2/187.
Thejappa, G, Bergamo, M, & MacDowall, R. J., E-mail: thejappa.golla@nasa.gov, E-mail: mbergamo@umd.edu, E-mail: Robert.MacDowall@nasa.gov. EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS. United States. https://doi.org/10.1088/0004-637X/745/2/187
Thejappa, G, Bergamo, M, and MacDowall, R. J., E-mail: thejappa.golla@nasa.gov, E-mail: mbergamo@umd.edu, E-mail: Robert.MacDowall@nasa.gov. 2012. "EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS". United States. https://doi.org/10.1088/0004-637X/745/2/187.
@article{osti_22011706,
title = {EMISSION PATTERNS OF SOLAR TYPE III RADIO BURSTS: STEREOSCOPIC OBSERVATIONS},
author = {Thejappa, G and Bergamo, M and MacDowall, R. J., E-mail: thejappa.golla@nasa.gov, E-mail: mbergamo@umd.edu, E-mail: Robert.MacDowall@nasa.gov},
abstractNote = {Simultaneous observations of solar type III radio bursts obtained by the STEREO A, B, and WIND spacecraft at low frequencies from different vantage points in the ecliptic plane are used to determine their directivity. The heliolongitudes of the sources of these bursts, estimated at different frequencies by assuming that they are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere, and the heliolongitudes of the spacecraft are used to estimate the viewing angle, which is the angle between the direction of the magnetic field at the source and the line connecting the source to the spacecraft. The normalized peak intensities at each spacecraft R{sub j} = I{sub j} /{Sigma}I{sub j} (the subscript j corresponds to the spacecraft STEREO A, B, and WIND), which are defined as the directivity factors are determined using the time profiles of the type III bursts. It is shown that the distribution of the viewing angles divides the type III bursts into: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field with angular width of {approx}2 Degree-Sign and (2) bursts emitting into a wider cone with angular width spanning from {approx} - 100 Degree-Sign to {approx}100 Degree-Sign . The plots of the directivity factors versus the viewing angles of the sources from all three spacecraft indicate that the type III emissions are very intense along the tangent to the spiral magnetic field lines at the source, and steadily fall as the viewing angles increase to higher values. The comparison of these emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.},
doi = {10.1088/0004-637X/745/2/187},
url = {https://www.osti.gov/biblio/22011706}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 745,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2012},
month = {Wed Feb 01 00:00:00 EST 2012}
}