scholarly journals Propagation of 10-50 mHz ULF waves with high spatial coherence at high latitudes

2001 ◽  
Vol 28 (2) ◽  
pp. 231-234 ◽  
Author(s):  
T. A. Howard ◽  
F. W. Menk
Keyword(s):  
Spatial Coherence ◽  
Ulf Waves ◽  
High Latitudes

ULF waves at very high latitudes

2006 ◽  
pp. 137-156 ◽  
Author(s):  
M. J. Engebretson ◽  
J. L. Posch ◽  
V. A. Pilipenko ◽  
O. M. Chugunova
Keyword(s):  
Ulf Waves ◽  
High Latitudes ◽  
Very High

scholarly journals A numerical model to investigate the polarisation azimuth of ULF waves through an ionosphere with oblique magnetic fields

2005 ◽  
Vol 23 (11) ◽  
pp. 3457-3471 ◽  
Author(s):  
M. D. Sciffer ◽  
C. L. Waters ◽  
F. W. Menk
Keyword(s):  
Magnetic Fields ◽  
Low Frequency ◽  
Wave Mode ◽  
Ulf Waves ◽  
High Latitudes ◽  
Wave Fields ◽  
One Dimensional ◽  
Ulf Wave ◽  
Dip Angle ◽  
Ground Wave

Abstract. A one dimensional, computational model for the propagation of ultra low frequency (ULF; 1-100 mHz) wave fields from the Earth's magnetosphere through the ionosphere, atmosphere and into the ground is presented. The model is formulated to include solutions for high latitudes where the Earth's magnetic field, (B0), is near vertical and for oblique magnetic fields applicable at lower latitudes. The model is used to investigate the wave polarisation azimuth in the magnetosphere compared with the ground wave fields, as a function of the dip angle of B0. We find that for typical ULF wave scale sizes, a 90° rotation of the wave polarisation azimuth from the magnetosphere to the ground occurs at high latitudes. However, this effect does not necessarily occur at lower latitudes in all cases. We show that the degree to which the wave polarisation azimuth rotates critically depends on the properties of the compressional ULF wave mode.

Large-amplitude ULF waves at high latitudes

2014 ◽  
Vol 119 ◽  
pp. 102-109 ◽  
Author(s):  
T. Guido ◽  
B. Tulegenov ◽  
A.V. Streltsov
Keyword(s):  
Large Amplitude ◽  
Ulf Waves ◽  
High Latitudes

scholarly journals Propagation of ULF waves through the ionosphere: Inductive effect for oblique magnetic fields

2004 ◽  
Vol 22 (4) ◽  
pp. 1155-1169 ◽  
Author(s):  
M. D. Sciffer ◽  
C. L. Waters ◽  
F. W. Menk
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Fields ◽  
Low Frequency ◽  
Shielding Effect ◽  
Ulf Waves ◽  
High Latitudes ◽  
Wave Fields ◽  
Faraday’S Law ◽  
Background Magnetic Field

Abstract. Solutions for ultra-low frequency (ULF) wave fields in the frequency range 1–100mHz that interact with the Earth's ionosphere in the presence of oblique background magnetic fields are described. Analytic expressions for the electric and magnetic wave fields in the magnetosphere, ionosphere and atmosphere are derived within the context of an inductive ionosphere. The inductive shielding effect (ISE) arises from the generation of an "inductive" rotational current by the induced part of the divergent electric field in the ionosphere which reduces the wave amplitude detected on the ground. The inductive response of the ionosphere is described by Faraday's law and the ISE depends on the horizontal scale size of the ULF disturbance, its frequency and the ionosphere conductivities. The ISE for ULF waves in a vertical background magnetic field is limited in application to high latitudes. In this paper we examine the ISE within the context of oblique background magnetic fields, extending studies of an inductive ionosphere and the associated shielding of ULF waves to lower latitudes. It is found that the dip angle of the background magnetic field has a significant effect on signals detected at the ground. For incident shear Alfvén mode waves and oblique background magnetic fields, the horizontal component of the field-aligned current contributes to the signal detected at the ground. At low latitudes, the ISE is larger at smaller conductivity values compared with high latitudes. Key words. Ionosphere (ionosphere-magnetosphere interactions; electric fields and currents; wave propagation)

Sources and velocities of Pc1-2 ULF waves at high latitudes

1995 ◽  
Vol 22 (21) ◽  
pp. 2965-2968 ◽  
Author(s):  
D. A. Neudegg ◽  
B. J. Fraser ◽  
F. W. Menk ◽  
H. J. Hansen ◽  
G. B. Burns ◽  
...  
Keyword(s):  
Ulf Waves ◽  
High Latitudes

Motions of neutral hydrogen at high latitudes

1967 ◽  
Vol 31 ◽  
pp. 265-278 ◽  
Author(s):  
A. Blaauw ◽  
I. Fejes ◽  
C. R. Tolbert ◽  
A. N. M. Hulsbosch ◽  
E. Raimond
Keyword(s):  
Surface Density ◽  
Velocity Dispersion ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
High Latitudes ◽  
Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° <l< 250°, + 40° <b< + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| < 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

Long-term Cyclic Variations of Prominences, Green and Red Coronae over Solar Cycles

2000 ◽  
Vol 179 ◽  
pp. 201-204
Author(s):  
Vojtech Rušin ◽  
Milan Minarovjech ◽  
Milan Rybanský
Keyword(s):  
Emission Lines ◽  
High Latitudes ◽  
Green Line ◽  
Solar Cycles ◽  
The South ◽  
Coronal Emission ◽  
Local Maxima ◽  
The North ◽  
Cyclic Variations

AbstractLong-term cyclic variations in the distribution of prominences and intensities of green (530.3 nm) and red (637.4 nm) coronal emission lines over solar cycles 18–23 are presented. Polar prominence branches will reach the poles at different epochs in cycle 23: the north branch at the beginning in 2002 and the south branch a year later (2003), respectively. The local maxima of intensities in the green line show both poleward- and equatorward-migrating branches. The poleward branches will reach the poles around cycle maxima like prominences, while the equatorward branches show a duration of 18 years and will end in cycle minima (2007). The red corona shows mostly equatorward branches. The possibility that these branches begin to develop at high latitudes in the preceding cycles cannot be excluded.

Quanitative aspects of electron diffraction using electron holography

1995 ◽  
Vol 53 ◽  
pp. 616-617
Author(s):  
E. Völkl ◽  
L.F. Allard ◽  
B. Frost ◽  
T.A. Nolan
Keyword(s):  
Electron Beam ◽  
Electron Diffraction ◽  
Software Package ◽  
Spatial Coherence ◽  
Electron Holography ◽  
Image Intensity ◽  
Interference Fringes ◽  
Complex Image ◽  
The Difference ◽  
Recorded Image

Off-axis electron holography has the well known ability to preserve the complex image wave within the final, recorded image. This final image described by I(x,y) = I(r) contains contributions from the image intensity of the elastically scattered electrons IeI (r) = |A(r) exp (iΦ(r)) |, the contributions from the inelastically scattered electrons IineI (r), and the complex image wave Ψ = A(r) exp(iΦ(r)) as:(1) I(r) = IeI (r) + Iinel (r) + μ A(r) cos(2π Δk r + Φ(r))where the constant μ describes the contrast of the interference fringes which are related to the spatial coherence of the electron beam, and Φk is the resulting vector of the difference of the wavefront vectors of the two overlaping beams. Using a software package like HoloWorks, the complex image wave Ψ can be extracted.

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