Gyroresonant wave-particle interactions in a dynamic magnetosphere

Journal Article · Sat Sep 01 04:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA095iA09p15103· OSTI ID:5452348

Gail, W B; Inan, U S; Helliwell, R A; Carpenter, D L ^[1]

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1. Stanford Univ., CA (USA)

Experimental and theoretical methods for studying gyroresonant wave-particle interactions (WPI) in the magnetosphere commonly assume that the magnetic field is static over the time scales of interest. In order to investigate the effect of nonequilibrium or dynamic magnetospheric processes on WPI, the response of the interaction mechanism to time-dependent perturbations in the magnetic field was examined using the global field compressions that occur during sudden commencements (sc). By measuring modifications of the wave spectrum and electron distribution during sc, the response of the WPI mechanism to slow variations in the magnetic field and plasma environment can be determined. This technique was used to examine the applicability of both nonlinear and quasi-linear descriptions of gyroresonant WPI to dynamic environments. Nonlinear interactions were invstigated by calculating the nonlinear parameters (interaction length, wave trapping threshold, and bunching efficiency) as a function of time for a given field line during a simulated sc compression. The results showed that the occurrence probability for discrete emissions generation increases during the compression, which is consistent with the observed triggering of discrete emissions during sc. Quasi-linear interactions were investigated using a modified formulation of quasi-linear theory in which a small time-dependent perturbation is introduced in the magnetic field and the resulting change int he wave growth rate is determined. The observed growth rate of 0.3-2.7 dB/s, total growth of 12-29 dB, and growth duration of 10-20 s were found to be comparable to the values of 1.5 dB/s, 30 dB, and 20 s predicted by the theory.

• OSTI ID: 5452348
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:A9; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CHARGED PARTICLES
COMPRESSION
DYNAMICS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTROMAGNETIC RADIATION
ENERGY TRANSFER
GEOMAGNETIC FIELD
INTERACTIONS
MAGNETIC FIELDS
MECHANICS
NONLINEAR PROBLEMS
QUASILINEAR PROBLEMS
RADIATION BELTS
RADIATIONS
SUDDEN COMMENCEMENTS
TIME DEPENDENCE
VARIATIONS