scholarly journals Determination of the Azimuthal Extent of Coherent E‐Region Scatter Using the ICEBEAR Linear Receiver Array

Radio Science ◽  
2021 ◽  
Vol 56 (3) ◽  
Author(s):  
Devin Huyghebaert ◽  
Kathryn McWilliams ◽  
Glenn Hussey ◽  
Draven Galeschuk ◽  
Jorge L. Chau ◽  
...  
Keyword(s):  
Receiver Array ◽  
Linear Receiver ◽  
E Region

A new approach to the determination of the E-region drift velocity using radar aurora doppler spectral shape

1996 ◽  
Vol 58 (1-4) ◽  
pp. 489-494
Author(s):  
V.G. Pivovarov ◽  
Yu.L. Sverdlov ◽  
N.G. Sergeeva ◽  
V.N. Lytkin
Keyword(s):  
Drift Velocity ◽  
Spectral Shape ◽  
New Approach ◽  
E Region

Determination of anisotropic velocity models from walkaway VSP data acquired in the presence of dip

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 723-729 ◽  
Author(s):  
Colin M. Sayers
Keyword(s):  
Transversely Isotropic ◽  
Seismic Profile ◽  
Slowness Surface ◽  
Velocity Models ◽  
Receiver Array ◽  
Strike Direction ◽  
Vsp Data ◽  
Walkaway Vsp ◽  
Oriented Parallel

Wide‐aperture walkaway vertical seismic profile (VSP) data acquired through transversely isotropic horizontal layers can be used to determine the P phase‐slowness surface, local to a receiver array in a borehole. In the presence of dip, errors in the slowness surface may occur if the medium is assumed to be layered horizontally. If the acquisition plane is oriented parallel to the dip direction, the derived slowness is too large for sources offset from the well in the down‐dip direction and too small for sources offset from the well in the up‐dip direction. For acquisition parallel to the strike of the layers, the recovery of the P phase‐slowness in the vicinity of the receiver array is excellent. It is therefore preferable to orient the walkaway VSP in the strike direction to estimate the anisotropic parameters of the medium in the vicinity of a receiver array. However, this may not be possible. If the dip direction of all layers has the same azimuth, the variation of walkaway traveltimes with azimuth has a simple form. This allows data from a single walkaway VSP extending both sides of a well to be inverted for the local anisotropic P phase‐slowness surface at the receivers even in the presence of dip. If data are acquired at more than one azimuth, the dip direction can be determined.

Determination of E region effective recombination coefficient using impulsive precipitation events

1992 ◽  
Vol 19 (5) ◽  
pp. 445-448 ◽  
Author(s):  
T. Nygrén ◽  
K. U. Kaila ◽  
A. Huuskonen ◽  
T. Turunen
Keyword(s):  
Recombination Coefficient ◽  
E Region ◽  
Precipitation Events

scholarly journals Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions

2004 ◽  
Vol 22 (8) ◽  
pp. 2819-2835 ◽  
Author(s):  
D. P. Monselesan ◽  
R. J. Morris ◽  
P. L. Dyson ◽  
M. R. Hyde
Keyword(s):  
Phase Velocity ◽  
Drift Velocity ◽  
Spatial Separation ◽  
Central Peak ◽  
Fluxgate Magnetometer ◽  
Angle Of Arrival ◽  
F Region ◽  
E Region ◽  
Gradient Drift

Abstract. During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background E-region reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7MHz, below the E-region critical frequency foE, have two side-peaks corresponding to Bragg scatter at approximately ±1-2Hz symmetrically located on each side of a central-peak corresponding to near-zenith total reflections. Angle-of-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the ExB direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler spectral signatures, observed at Casey in December 1996 during SEC/lacuna conditions may be linked to ionosphere irregularities. These irregularities may possibly be generated by primary plasma waves triggered by current-driven instabilities, that is to say, a hybrid of the "modified two-stream" and "gradient drift" instability mechanisms.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

Distance to SN 1987A and the LMC

1999 ◽  
Vol 190 ◽  
pp. 549-554
Author(s):  
Nino Panagia
Keyword(s):  
Angular Size ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Light Curves ◽  
Distance Modulus ◽  
Absolute Size ◽  
Sn 1987A

Using the new reductions of the IUE light curves by Sonneborn et al. (1997) and an extensive set of HST images of SN 1987A we have repeated and improved Panagia et al. (1991) analysis to obtain a better determination of the distance to the supernova. In this way we have derived an absolute size of the ringRabs= (6.23 ± 0.08) x 1017cm and an angular sizeR″ = 808 ± 17 mas, which give a distance to the supernovad(SN1987A) = 51.4 ± 1.2 kpc and a distance modulusm–M(SN1987A) = 18.55 ± 0.05. Allowing for a displacement of SN 1987A position relative to the LMC center, the distance to the barycenter of the Large Magellanic Cloud is also estimated to bed(LMC) = 52.0±1.3 kpc, which corresponds to a distance modulus ofm–M(LMC) = 18.58±0.05.

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