scholarly journals Ionospheric electron heating, optical emissions, and striations induced by powerful HF radio waves at high latitudes: Aspect angle dependence

2003 ◽  
Vol 108 (A4) ◽  
Author(s):  
M. T. Rietveld
Keyword(s):  
High Latitudes ◽  
Radio Waves ◽  
Electron Heating ◽  
Optical Emissions ◽  
Aspect Angle ◽  
Angle Dependence

Aspect angle dependence of the radar aurora Doppler velocity

1994 ◽  
Vol 99 (A2) ◽  
pp. 2131 ◽  
Author(s):  
A. V. Kustov ◽  
M. V. Uspensky ◽  
G. J. Sofko ◽  
J. A. Koehler ◽  
J. Mu
Keyword(s):  
Doppler Velocity ◽  
Aspect Angle ◽  
Angle Dependence

scholarly journals An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra

2005 ◽  
Vol 23 (1) ◽  
pp. 55-74 ◽  
Author(s):  
◽  
Yu. Yurik ◽  
La Hoz ◽  
◽  
◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Electromagnetic Emission ◽  
Density Fluctuations ◽  
Spectral Features ◽  
Langmuir Turbulence ◽  
Angular Structure ◽  
Frequency Spectra ◽  
Aspect Angle ◽  
Angle Dependence ◽  
Stimulated Electromagnetic Emission

Abstract. When the Earth's ionosphere is irradiated by a radiofrequency (RF) electromagnetic wave of sufficiently high power density and tuned to match a natural E- or F-region plasma frequency, ionospheric magnetoionic wave modes may be excited and may generate RF electromagnetic sideband waves via nonlinear interactions. These secondary emissions, which may then escape from the ionosphere, have been termed stimulated electromagnetic emission or SEE. The frequency spectra of this radiation has been studied extensively, and a number of characteristic spectral features have been identified and in some cases related to particular plasma processes. The separation in frequency between the RF pump and the harmonics of the local electron gyrofrequency is critical in determining the amount of anomalous absorption suffered by the pump wave and the spectral properties of the stimulated sidebands. The pump can excite electrostatic waves which do not propagate away but can in some cases be observed via radio-wave scattering from the electron density fluctuations associated with them. These enhanced density fluctuations are created by processes commonly referred to as upper-hybrid and Langmuir turbulence. Langmuir turbulence has been the subject of 930-MHz scattering observations with antenna scanning through several pre-selected angles between the geographic and geomagnetic zenith directions, and a preference for pointing angles between the Spitze angle and geomagnetic field-aligned was identified. Other phenomena, such as the generation of enhanced electron temperatures and artificial aurora, have more recently been shown to have special behavior at similar angles, near but apparently not quite at field-aligned. In view of this evidence for angular structure in several pump-induced effects, in light of the rich variety of SEE phenomena strongly dependent on the geomagnetic field via the frequency interval between the pump and the gyrofrequency harmonics, and in view of the not yet understood but complex relationship between electrostatic fluctuations and SEE, it is of interest to investigate experimentally whether a similar angular structure is present in the various spectral features of the SEE signals and to compare the results with radar and other observations of RF-pump-induced effects. To this end we describe a simple two-element radio interferometer designed to search for aspect angle dependence of SEE features. We present an example of the initial data produced by this system, and draw preliminary conclusions based on the example data.

Magnetic aspect angle dependence of spectra from coherent radio aurora backscatter

1989 ◽  
Vol 94 (A4) ◽  
pp. 3663 ◽  
Author(s):  
J. Watermann ◽  
D. R. McDiarmid ◽  
J. A. Koehler ◽  
G. J. Sofko ◽  
A. G. McNamara
Keyword(s):  
Aspect Angle ◽  
Angle Dependence

Aspect angle dependence of HF enhanced incoherent backscatter

1999 ◽  
Vol 24 (8) ◽  
pp. 1003-1006 ◽  
Author(s):  
B. Isham ◽  
M.T. Rietveld ◽  
T. Hagfors ◽  
C. La Hoz ◽  
E. Mishin ◽  
...  
Keyword(s):  
Aspect Angle ◽  
Angle Dependence

scholarly journals Artificial optical emissions at HAARP for pump frequencies near the third and second electron gyro-harmonic

2005 ◽  
Vol 23 (5) ◽  
pp. 1585-1592 ◽  
Author(s):  
M. J. Kosch ◽  
T. Pedersen ◽  
J. Hughes ◽  
R. Marshall ◽  
E. Gerken ◽  
...  
Keyword(s):  
High Frequency ◽  
Optical Emission ◽  
Particle Interactions ◽  
Auroral Ionosphere ◽  
Radio Waves ◽  
Pump Frequency ◽  
Optical Emissions ◽  
The Third ◽  
Active Experiments ◽  
First Time

Abstract. High-power high-frequency radio waves beamed into the ionosphere cause plasma turbulence, which can accelerate electrons. These electrons collide with the F-layer neutral oxygen causing artificial optical emissions identical to natural aurora. Pumping at electron gyro-harmonic frequencies has special significance as many phenomena change their character. In particular, artificial optical emissions become strongly reduced for the third and higher gyro-harmonics. The High frequency Active Auroral Research Program (HAARP) facility is unique in that it can select a frequency near the second gyro-harmonic. On 25 February 2004, HAARP was operated near the third and passed through the second gyro-harmonic for the first time in a weakening ionosphere. Two novel observations are: firstly, a strong enhancement of the artificial optical emission intensity near the second gyro-harmonic, which is opposite to higher gyro-harmonics; secondly, the optical enhancement maximum occurs for frequencies just above the second gyro-harmonic. We provide the first experimental evidence for these effects, which have been predicted theoretically. In addition, irregular optical structures were created when the pump frequency was above the ionospheric critical frequency.Keywords. Active experiments – Auroral ionosphere – Wave-particle interactions

Aspect angle dependence of irregularity phase velocities in the auroral electrojet

1980 ◽  
Vol 7 (12) ◽  
pp. 1081-1084 ◽  
Author(s):  
T. Ogawa ◽  
B. B. Balsley ◽  
W. L. Ecklund ◽  
D. A. Carter ◽  
P. E. Johnston
Keyword(s):  
Auroral Electrojet ◽  
Aspect Angle ◽  
Angle Dependence ◽  
Phase Velocities

Flow and aspect angle dependence of 3-m irregularities in the auroral E region

1989 ◽  
Vol 94 (A2) ◽  
pp. 1501 ◽  
Author(s):  
Dieter André ◽  
George J. Sofko ◽  
James A. Koehler ◽  
Allen G. McNamara ◽  
Bruce A. McIntosh
Keyword(s):  
Aspect Angle ◽  
Angle Dependence ◽  
E Region
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