Numerical simulation and theory of strong ionospheric gradient-drift turbulence

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1978

OSTI ID:5671217

Keskinen, M J

Numerical and analytical studies are made of the nonlinear development of the gradient-drift or E x B instability using the mathematical model that describes the Type II irregularities in the E region equatorial electrojet. Using a two-dimensional electrostatic fluid code with parameters typical of the daytime electrojet, the temporal and spatial power spectra are computed over a much larger range of wavelengths (9 to 128 m) than is presently studied with radar. The mean frequencies obtained agree well with linear theory except at short wavelengths while the linewidths are greater by up to an order of magnitude than the linear damping rates. For the linearly damped modes at a particular wavelength of the linewidths increase with increasing electron drift velocity contrary to linear theory while at a fixed drift velocity the linewidths increase with decreasing wavelength. For three drift velocities (75, 100, 125 msec/sup -1/) the time averaged spatial power spectra are found to be essentially isotropic. Analytically, the direct interaction approximation of Kraichnan as modified by Kadomtsev is employed to develop a strong turbulence theory which predicts both a nonlinear wave damping GAMMA/sub k/proportional V/sub d/k/sup 2/I/sub k//sup 1/2/, and a power law for the two-dimensional spectrum I/sub k/proportional k/sup -n/ with n approx. = 3.2, where V/sub d/ is the electron drift due to the electrojet current. Favorable comparisons are made among the numerical and analytical resuts and available experimental observations. In addition, the theory is extended to treat the case of a two-dimensional, homogeneous, low-pressure, weakly-ionized plasma driven unstable by an externally applied pump wave of the form E/sub 0/ cos (k/sub 0/ . x - ..omega../sub 0/t). Finally, a comparison is made between Kraichnan's direct-interaction approximation and Kadomtsev's strong turbulence-weak coupling theory.

• Research Organization: Cornell Univ., Ithaca, NY (USA)
• OSTI ID: 5671217
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CURRENTS
DAMPING
E REGION
EARTH ATMOSPHERE
ELECTRIC CURRENTS
ELECTROJETS
ELECTRON DRIFT
INSTABILITY
IONOSPHERE
MATHEMATICAL MODELS
PLANETARY IONOSPHERES
SPECTRA
TURBULENCE
VELOCITY