Electromagnetic ion cyclotron waves in the plasma depletion layer

Journal Article · Sun Aug 01 04:00:00 EDT 1993 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JA00796· OSTI ID:96498

Denton, R E; Hudson, M K ^[1]; Fuselier, S A ^[2]; Anderson, B J ^[3]

---

1. Dartmouth College, Hanover, NH (United States)
2. Lockheed Palo Alto Research Lab., CA (United States)
3. Johns Hopkins Univ., Laurel, MD (United States)

The authors have studied the theoretical properties of electromagnetic ion cyclotron (EMIC) waves which occur in the plasma depletion layer. Their analysis assumes a homogeneous plasma with the characteristics which were measured by the AMPTE/CCE satellite at 1450-1501 UT on October 5, 1984. During this time, waves were observed in the Pc 1 frequency range (0.2-5 Hz) below the hydrogen gyrofrequency, and they identify these waves as EMIC waves. In agreement with observations, the theory predicts two frequency bands of waves, above and below about 0.4 {Omega}{sub H}, where {Omega}{sub H} is the hydrogen gyrofrequency. The higher-frequency instability is driven by the temperature anisotropy of the H{sup +} ions, while the lower-frequency instability is driven by the temperature anisotropy of the He{sup 2+} ions. These two frequency bands occur on the same dispersion surface. The EMIC waves tend to quasi-linearly control the value of the proton temperature ratio T{sub {perpendicular}}/T{sub {parallel}} by an increase in T{sub {parallel}} due to scattering so that the bulk plasma stays near marginal stability. Here, T{sub {parallel}}(T{sub {perpendicular}}) is the temperature parallel (perpendicular) to B{sub 0}. Without convective effects, the nonlinear wave amplitude tends to be large over the entire angular range 0 {le} {theta}{sub kB} {le} 75{degrees}, where {theta}{sub kB} is the angle between the wave vector and the background magnetic field (B{sub 0}). However, waves for which the perpendicular (B{sub 0}) group velocity v{sub g{perpendicular}} is large, are likely to be convectively limited in growth. It is likely that the higher-frequency waves will have k roughly parallel to B{sub 0} and will be left-hand polarized, while the lower-frequency wave band will have k oblique to B{sub 0} and will be linearly polarized, in agreement with observations. 38 refs., 9 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 96498
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A8 Vol. 98; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
EARTH MAGNETOSPHERE
ENERGY SPECTRA
INTERPLANETARY MAGNETIC FIELDS
ION CYCLOTRON-RESONANCE
ION PLASMA WAVES
POLARIZATION
SHOCK WAVES