Velocity shear and fluctuations in the auroral regions of the ionosphere

Journal Article · Mon May 01 00:00:00 EDT 1989 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA094iA05p05316· OSTI ID:6271911

Basu, B; Coppi, B

The theory of collisional electrostatic modes that are given unstable by a sheared field-aligned ion flow velocity (i.e., V/sub i//sub 0/ = V/sub 0/(x)e/sub z/, B/sub 0/ = B/sub 0/e/sub z/) is presented. The instability threshold condition is chemically bond dV/sub 0//dx chemically bond>2(1 +T/sub i//T/sub e/)..nu../sub i//sub n/, where ..nu../sub i//sub n/ is the ion-neutral collision frequency, the characteristic longitudinal wavelengths lambda/sub parallel/>lambda/sub e/, lambda/sub e/ being the electron collision mean free path, and the transverse wavelengths lambda/sub perpendicular/>2/sup 1/2/ ..pi..rho/sub i/, rho/sub i/ being the ion gyroradius. The linearly unstable modes can account for fluctuations with transverse wavelengths ranging from a kilometer to several meters for only a moderate amount of shear (in the parallel velocity). Thus the instability provides a direct means of exciting almost the entire range of the observed (Basu et al., 1988) subkilometer scale irregularities in the auroral F region. The quasi-linear analysis presented here shows that an effective viscosity describing momentum transport in the x direction can be derived in the presence of the shear-driven fluctuations. The spatial profiles of the excited modes are evaluated from the solution of the appropriate dispersion equation. A model is proposed to describe the nonlinear evolution of the instability while ensuring that the characteristics of the turbulent fluctuation spectra resulting from it are consistent with those of the observed spectra.

• Research Organization: Air Force Geophysics Laboratory, Hanscom Air Force Base, Massachusetts
• OSTI ID: 6271911
• Journal Information: J. Geophys. Res.; (United States), Vol. 94:A5
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
F REGION
PLASMA DENSITY
AURORAL ZONES
COLLISIONAL PLASMA
EXPLORER SATELLITES
HELMHOLTZ INSTABILITY
ION DRIFT
SHEAR
EARTH ATMOSPHERE
INSTABILITY
IONOSPHERE
PLANETARY IONOSPHERES
PLASMA
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
SATELLITES
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena