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 Simultaneous HF measurements of E- and F-region Doppler velocities at large flow angles

2004 ◽  
Vol 22 (4) ◽  
pp. 1177-1185 ◽  
Author(s):  
R. A. Makarevitch ◽  
F. Honary ◽  
A. V. Koustov
Keyword(s):  
Hf Radar ◽  
Doppler Velocity ◽  
Plasma Convection ◽  
Aspect Angle ◽  
F Region ◽  
Significant Difference ◽  
E Region ◽  
The Difference ◽  
New Feature ◽  
Large Flow

Abstract. Data collected by the CUTLASS Finland HF radar are used to illustrate the significant difference between the cosine component of the plasma convection in the F-region and the Doppler velocity of the E-region coherent echoes observed at large flow angles. We show that the E-region velocity is ~5 times smaller in magnitude and rotated by ~30° clockwise with respect to convection in the F-region. Also, measurements at flow angles larger than 90° exhibit a completely new feature: Doppler velocity increase with the expected aspect angle and spatial anticorrelation with the backscatter power. By considering DMSP drift-meter measurements we argue that the difference between F- and E-region velocities cannot be interpreted in terms of the convection change with latitude. The observed features in the velocity of the E-region echoes can be explained by taking into account the ion drift contribution to the irregularity phase velocity as predicted by the linear fluid theory. Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; plasma convection)

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

Particle-in-cell plasma simulations of the modified two-stream instability

1994 ◽  
Vol 12 (10/11) ◽  
pp. 1091-1100 ◽  
Author(s):  
K. Schlegel ◽  
H. Thiemann
Keyword(s):  
Doppler Velocity ◽  
Plasma Parameters ◽  
Particle In Cell ◽  
Aspect Angle ◽  
Similar Work ◽  
Cell Plasma ◽  
E Region ◽  
Unstable Plasma ◽  
Stream Instability ◽  
Good Agreement

Abstract. We model the modified two-stream plasma instability occurring in the ionospheric E-region using a 2.5-dimensional particle-in-cell code. Compared to previous similar work we concentrate on simulated quantities that can easily be measured in the real ionosphere by coherent radars or rockets, such as the Doppler velocity, the backscattered power, backscattered spectra, aspect angle behaviour and electron temperature enhancement. Despite using a relatively small simulation model, we obtain remarkably good agreement between actual observed and simulated plasma parameters. The advantage of such a small system is that we were able to perform (other than in previous related work) many simulation runs with different sets of input parameters, thus studying the unstable plasma under various conditions.

scholarly journals Meridional motions of the afternoon radar aurora, auroral electrojets, and absorption patches under variable IMF conditions

2004 ◽  
Vol 22 (5) ◽  
pp. 1649-1664
Author(s):  
R. A. Makarevitch ◽  
F. Honary ◽  
A. V. Koustov ◽  
M. V. Uspensky
Keyword(s):  
Electric Fields ◽  
Temporal Correlation ◽  
Doppler Velocity ◽  
Plasma Convection ◽  
Motion Patterns ◽  
Aspect Angle ◽  
Radar Echoes ◽  
Meridional Motion ◽  
E Region ◽  
The Imf

Abstract. The meridional motions of the CUTLASS HF and STARE VHF coherent echoes, IMAGE equivalent electrojet currents, and IRIS absorption patches during the postnoon/early-evening event of 14 February 2000 are presented. The motions were found to be synchronous, to a first approximation, for all instruments. The temporal correlation between motions in the radar and magnetometer data was exceptionally good, although spatially the areas with the E-region backscatter and most intense equivalent currents were not coincident, with the HF (VHF) echoes being shifted 100–200km (20–50km) equatorward (poleward). The meridional motions of the radar echoes and electrojet currents appeared to be controlled by the IMF Bz changes; the meridional propagation direction was equatorward (poleward) during the intervals when the IMF was southward (northward), with one exception when the poleward progression continued after the IMF southward turning. We relate the observed meridional motion patterns to the polar cap expansion/contraction during variable IMF conditions and discuss the relative importance of two types of processes: the dayside reconnection and IMF-triggered substorms. We also investigate the irregularity Doppler velocity for the STARE (144MHz) and CUTLASS (12MHz) observations at large flow angles in the context of the eastward and westward electrojet systems. We show that the 144-MHz Doppler velocity is determined by a combination of two factors: the sense of electrojet currents and the aspect angle conditions within the STARE field of view. Finally, the behavior of small dayside enhancements of the IRIS absorption (up to 0.5dB at 38.2MHz) accompanying the radar echoes and electrojet currents is examined. Since the velocity of the meridional displacements was close to that of the poleward/equatorward progressing intense currents, it is suggested that the absorption patches observed during the event were related to the heating of the E-region plasma by the unstable plasma waves in the regions of enhanced electric fields. Key words. Ionosphere (auroral ionosphere; electric fields and currents; plasma convection)

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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