Low-altitude ISIS 1 observations of auroral radio emissions and their significance to the cyclotron maser instability

Journal Article · Sun Feb 01 04:00:00 EST 1987 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA092iA02p01218· OSTI ID:5558018

Benson, R F ^[1]; Wong, H K ^[2]

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1. NASA Goddard Space Flight Center, Greenbelt, MD (United States)
2. Southwest Research Inst., San Antonio, TX (United States)

Low-altitude ISIS 1 observations are presented which support the cyclotron maser instability as the generation mechanism of most, but not all, auroral radio emissions. The observations confirm the ability of the mechanism to generate different wave modes and harmonics as the ratio of the plasma frequency to gyrofrequency f{sub N}/f{sub H} increases depending on the form of the energetic electron distribution function. The present observations correspond to conditions where f{sub N}/f{sub H} is always larger than 0.2 and is typically {approximately}1.0. The observations and instability growth rate calculations indicate that second harmonic radiation in the extraordinary and the Z modes is directly generated at low altitudes. By far the most common signals observed near ISIS 1 perigee, however, are in the fundamental Z and whistler modes. The observations and calculations in the case of the Z mode suggest that the pertinent process involves a maser that does not saturate, i.e., that group velocity effects are important. The whistler mode is the most intense signal observed at low altitudes. Since the cyclotron maser generated whistler mode waves have peak growth rates for downward field-aligned propagation, they should be able to penetrate the ionosphere. This process may provide the explanation of occasional reports, dating back to the International Geophysical Year time period, of ground level detection of radio noise ({approximately}100 kHz) associated with the aurora.

• OSTI ID: 5558018
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 92:A2; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAE
AURORAL ZONES
CYCLOTRON INSTABILITY
ELECTROMAGNETIC RADIATION
EMISSION
GROUND LEVEL
INSTABILITY
INSTABILITY GROWTH RATES
LANGMUIR FREQUENCY
LEVELS
NOISE
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
RADIATIONS
RADIO NOISE
RADIOWAVE RADIATION
SATELLITES
WHISTLERS