Aspect sensitivity of equatorial electrojet irregularities and theoretical implications
- Univ. of Illinois, Urbana (United States)
- Cornell Univ., Ithaca, NY (United States)
The authors used a multi baseline 50-MHz radar interferometer at the Jicamarca Radio Observatory to study the dependence of echo strength on the aspect angle, the angle of arrival relative to normal to the geomagnetic field. They observed rms values of this angle in the range 0.1{degree}-0.4{degree}, which implies an aspect sensitivity somewhat greater than the nominal 10 dB/deg often quoted for auroral echoes. The technique has sufficient resolution to allow deviations from normal of less than 0.1{degree} to be measured fairly easily, and they were able to determine variations of the aspect sensitivity with altitude, Doppler shift, and electrojet conditions. During weakly driven periods, when only type 2 echoes were observed, the width, or rms angular deviation from normal, decreased monotonically with increasing altitude, as simple linear theory would suggest, but the variation was less rapid than the variation of {nu}{sub e}/{Omega}{sub e}, especially on the bottomside of the electrojet. A particularly interesting observation was that; during strongly driven type 1 conditions, there was a pronounced variation of width with Doppler shift. The width for small phase velocities was sometimes more than twice that at the ion-acoustic velocity. They believe that this broadening is due to nonlinear three-wave mode coupling which produces a reverse cascade of energy from short wavelengths to long and an increase in the mean aspect angle. Such a cascade represents an increase in the effective diffusion coefficient for the short wavelength waves and so could provide an explanation alternative to that of the anomalous collision process of Sudan (1983) for the limitation of the type 1 phase velocity at the ion-acoustic velocity.
- OSTI ID:
- 5994729
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 94:A1; ISSN JGREA; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
CURRENTS
DOPPLER EFFECT
EARTH ATMOSPHERE
ELECTRIC CURRENTS
ELECTROJETS
EQUATOR
GEOMAGNETIC FIELD
IONOSPHERE
MAGNETIC FIELDS
MEASURING INSTRUMENTS
MEASURING METHODS
PHASE VELOCITY
PLANETARY IONOSPHERES
PLASMA DENSITY
RADAR
RANGE FINDERS
SENSITIVITY
VARIATIONS
VELOCITY