Observations of electron conics by the Viking satellite

Details Observations of electron conics by the Viking satellite Observations of electron conics by the Viking satellite

Jun 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996jgr...10113225e&link_type=abstract

Journal of Geophysical Research, Volume 101, Issue A6, p. 13225-13238

Physics

Plasma Physics

9

Ionosphere: Wave/Particle Interactions, Magnetospheric Physics: Auroral Phenomena, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions, Space Plasma Physics: Charged Particle Motion And Acceleration

Scientific paper

Electron angular distributions peaked at oblique angles to the magnetic field, electron conics, are frequently found in the Viking data at all magnetic local times, but with a maximum in the dusk sector. Several types of electron conics have been observed by Viking as well as by other satellites. One type is frequently seen below the acceleration region. It is caused by adiabatic motion of electrons with a field-aligned distribution that has a broader angular width than the loss cone. The atmospheric loss of particles will result in a distribution peaked at pitch angles close to the loss cone. Another type is due to heating or acceleration processes at low altitudes and is seen above the acceleration region. Particle and wave characteristics and possible generation mechanisms for this type of electron conic are discussed. The ion and electron angular distributions observed by Viking indicate that a parallel electric field is present below Viking during this type of event. Ion observations give important information on the processes that produce the electron conics. Almost 200 electron conic events have been detected in the Viking data, that is, in about every third orbit that was studied. Their frequency of occurrence in altitude maximizes in the upper part of the acceleration region, between 10,000 and 11,000 km. The number of events are found to decrease at higher altitudes. This might indicate that diffusion processes, associated with wave generation, remove the anisotropy in the electron distribution function in and above the acceleration region. Wave observations show the presence of both low-frequency waves and waves close to the electron gyro frequency. Acceleration in a fluctuating (approximately 1 Hz) parallel electric field is suggested as a likely mechanism to create the electron conics observed by Viking. The period of the fluctuations is comparable to the travel time, below the acceleration region, of the electrons forming the conic distribution.

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