scholarly journals Nonlinear evolution of thermal self-focusing instability in ionospheric modifications at high latitudes: Aspect angle dependence

2006 ◽  
Vol 33 (16) ◽  
Author(s):  
N. A. Gondarenko ◽  
S. L. Ossakow ◽  
G. M. Milikh
Keyword(s):  
Nonlinear Evolution ◽  
High Latitudes ◽  
Aspect Angle ◽  
Angle Dependence ◽  
Self Focusing

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 Nonlinear evolution of Langmuir and electromagnetic pulses in a warm, unmagnetized plasma: modulational instability, integrability and self-focusing in 2 + 1 dimensions

1994 ◽  
Vol 52 (1) ◽  
pp. 75-90
Author(s):  
Ronald E. Kates ◽  
D. J. Kaup
Keyword(s):  
Nonlinear Evolution ◽  
Modulational Instability ◽  
Soliton Solutions ◽  
Integrable Case ◽  
Regime Parameter ◽  
Self Focusing ◽  
Long Time ◽  
Unmagnetized Plasma ◽  
Modulational Instabilities ◽  
Parameter Values

The nonlinear dynamics of wave envelopes modulated in 2 + 1 dimensions is considered for two systems in plasma physics: (i) Langmuir pulses and (ii) intense (but weakly relativistic) electromagnetic (EM) pulses. Using singular perturbation techniques applied to an envelope approximation, both problems are reduced to the two-dimensional nonlinear Schrödinger (2DNLS) system, which describes the dynamics of two coupled slowly varying potentials. The general 2DNLS system exhibits a rich variety of phenomena, including enhanced (compared with ‘longitudinal’ propagation) modulational stability and (1D) soliton formation; decay of 1D solitons over long time scales; self- focusing regimes (determined by a virial-type condition); as well as integrability and 2D solitons. Applying our recent results on the 2DNLS system, we determine which of these phenomena can actually occur here and compute the parameter regimes. (i) The 2DNLS system for the Zakharov equations is modulationally unstable for all parameter values. It also has an integrable sector and a self-focusing regime. (ii) The 2DNLS system describes coupled ‘longitudinal’ and ‘transverse’ modulations of linearly or circularly polarized EM pulses propagating through a warm unmagnetized two-component neutral plasma with arbitrary masses (i.e. electron—positron or electron—ion). The pulse can accelerate particles to weakly (but not fully) relativistic velocities; relativistic, ponderomotive and harmonic effects all contribute to the nonlinear terms. The resulting 2DNLS system does not admit a self-focusing regime. Parameter values leading to an integrable case (the so-called ‘Davey—Stewartson I’ equations, which admit 2D soliton solutions) are computed; however, the required values would not be attainable in a laboratory or astrophysical setting. None the less, the existence of new nonlinear modulational instabilities associated with the second spatial degree of freedom already represents an important potential limitation on any (1 + 1)-dimensional approach to nonlinear evolution and modulational instability of plasma EM waves.

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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