scholarly journals Ray tracing of whistler-mode chorus elements: implications for generation mechanisms of rising and falling tone emissions

2013 ◽  
Vol 31 (4) ◽  
pp. 665-673 ◽  
Author(s):  
K. Yamaguchi ◽  
T. Matsumuro ◽  
Y. Omura ◽  
D. Nunn
Keyword(s):  
Ray Tracing ◽  
Low Frequency ◽  
Equatorial Region ◽  
Lower Hybrid ◽  
Wave Pulse ◽  
Generation Region ◽  
Field Lines ◽  
Generation Mechanisms ◽  
Tone Generation ◽  
Lower Hybrid Resonance

Abstract. Using a well-established magnetospheric very-low-frequency (VLF) ray tracing method, in this work we trace the propagation of individual rising- and falling-frequency elements of VLF chorus from their generation point in the equatorial region of the magnetosphere through to at least one reflection at the lower-hybrid resonance point. Unlike recent work by Bortnik and co-workers, whose emphasis was on demonstrating that magnetospheric hiss has its origins in chorus, we here track the motion in the equatorial plane of the whole chorus element, paying particular regard to movement across field lines, rotation, and compression or expansion of the wave pulse. With a generation point for rising chorus at the equator, it was found the element wave pulse remained largely field aligned in the generation region. However, for a falling tone generation point at 4000 km upstream from the equator, by the time the pulse crosses the equator the wavefield had substantial obliquity, displacement, and compression, which has substantial implications for the theory of falling chorus generation.

scholarly journals On the dispersion law of low-frequency electron whistler waves in a multi-ion plasma

2008 ◽  
Vol 26 (6) ◽  
pp. 1605-1615 ◽  
Author(s):  
B. V. Lundin ◽  
C. Krafft
Keyword(s):  
Cutoff Frequency ◽  
Low Frequency ◽  
Negative Ions ◽  
Plasma Electron ◽  
Lower Hybrid ◽  
Charged Dust ◽  
Whistler Waves ◽  
Dispersion Law ◽  
Ion Plasma ◽  
Lower Hybrid Resonance

Abstract. A new and simple dispersion law for extra-low-frequency electron whistler waves in a multi-ion plasma is derived. It is valid in a plasma with finite ratio ωc/ωpe of electron gyro-to-plasma frequency and is suitable for wave frequencies much less than ωpe but well above the gyrofrequencies of most heavy ions. The resultant contribution of the ions to the dispersion law is expressed by means of the lower hybrid resonance frequency, the highest ion cutoff frequency and the relative content of the lightest ion. In a frequency domain well above the ions' gyrofrequencies, this new dispersion law merges with the "modified electron whistler dispersion law" determined in previous works by the authors. It is shown that it fits well to the total cold plasma electron whistler dispersion law, for different orientations of the wave vectors and different ion constituents, including negative ions or negatively charged dust grains.

scholarly journals A mechanism for heating electrons in the magnetopause current layer and adjacent regions

2011 ◽  
Vol 29 (12) ◽  
pp. 2305-2316 ◽  
Author(s):  
A. Roux ◽  
P. Robert ◽  
O. Le Contel ◽  
V. Angelopoulos ◽  
U. Auster ◽  
...  
Keyword(s):  
Low Frequency ◽  
Sheet Thickness ◽  
Equatorial Region ◽  
Current Layer ◽  
Electron Temperature Gradient ◽  
Spatial Gradients ◽  
Short Transverse ◽  
Field Lines ◽  
High Beta ◽  
String Of Pearls

Abstract. Taking advantage of the string-of-pearls configuration of the five THEMIS spacecraft during the early phase of their mission, we analyze observations taken simultaneously in the magnetosheath, the magnetopause current layer and the magnetosphere. We find that electron heating coincides with ultra low frequency waves. It seems unlikely that electrons are heated by these waves because the electron thermal velocity is much larger than the Alfvén velocity (Va). In the short transverse scale (k⊥ρi >> 1) regime, however, short scale Alfvén waves (SSAWs) have parallel phase velocities much larger than Va and are shown to interact, via Landau damping, with electrons thereby heating them. The origin of these waves is also addressed. THEMIS data give evidence for sharp spatial gradients in the magnetopause current layer where the highest amplitude waves have a large component δB perpendicular to the magnetopause and k azimuthal. We suggest that SSAWs are drift waves generated by temperature gradients in a high beta, large Ti/Te magnetopause current layer. Therefore these waves are called SSDAWs, where D stands for drift. SSDAWs have large k⊥ and therefore a large Doppler shift that can exceed their frequencies in the plasma frame. Because they have a small but finite parallel electric field and a magnetic component perpendicular to the magnetopause, they could play a key role at reconnecting magnetic field lines. The growth rate depends strongly on the scale of the gradients; it becomes very large when the scale of the electron temperature gradient gets below 400 km. Therefore SSDAW's are expected to limit the sharpness of the gradients, which might explain why Berchem and Russell (1982) found that the average magnetopause current sheet thickness to be ~400–1000 km (~500 km in the near equatorial region).

SOME CHARACTERISTICS OF THE LOWER HYBRID RESONANCE NOISE BANDS OBSERVED BY THE ALOUETTE I SATELLITE

1967 ◽  
Vol 45 (1) ◽  
pp. 13-19 ◽  
Author(s):  
D. J. McEwen ◽  
R. E. Barrington
Keyword(s):  
Low Frequency ◽  
Lower Hybrid ◽  
Frequency Of Occurrence ◽  
Maximum Frequency ◽  
Very Low Frequency ◽  
Hybrid Resonance ◽  
Different Types ◽  
Excitation Mechanisms ◽  
Night And Day ◽  
Lower Hybrid Resonance

An investigation has been made of the occurrence as a function of latitude and time of lower hybrid resonance (LHR) noise bands as recorded during 1963 and 1964 by the very-low-frequency receiver aboard the Alouette I satellite. Two different types of LHR noise are observed—polar and mid-latitude. Polar LHR noise bands, with the maximum frequency of occurrence at about 75° invariant latitude, are observed approximately one half of the time throughout the year and during both night and day. Mid-latitude LHR noise bands have a maximum frequency of occurrence at about 55° and are observed mainly during the months of June–October and primarily at night. The differences in appearance and occurrence of these two types of LHR noise suggest different excitation mechanisms.

scholarly journals LHR effects in nonducted whistler propagation – new observations and numerical modelling

2001 ◽  
Vol 19 (2) ◽  
pp. 147-157 ◽  
Author(s):  
F. Jiřiček ◽  
D. R. Shklyar ◽  
P. Třiska
Keyword(s):  
Wave Propagation ◽  
Numerical Modelling ◽  
Plasma Frequency ◽  
Cutoff Frequency ◽  
Lower Hybrid ◽  
Noise Band ◽  
Maximum Value ◽  
Lower Hybrid Resonance ◽  
Whistler Propagation ◽  
Lower Cutoff

Abstract. VLF-ELF broadband measurements onboard the MAGION 4 and 5 satellites at heights above 1 Re in plasmasphere provide new data on various known phenomena related to ducted and nonducted whistler wave propagation. Two examples are discussed: magnetospherically reflected (MR) whistlers and lower hybrid resonance (LHR) noise band. We present examples of rather complicated MR whistler spectrograms not reported previously and argue the conditions for their generation. Analytical consideration, together with numerical modelling, yield understanding of the main features of those spectrograms. LHR noise band, as well as MR whistlers, is a phenomenon whose source is the energy propagating in the nonducted way. At the plasmaspheric heights, where hydrogen (H+) is the prevailing ion, and electron plasma frequency is much larger than gyrofrequency, the LHR frequency is close to its maximumvalue in a given magnetic field. This frequency is well followed by the observed noise bands. The lower cutoff frequency of this band is somewhat below that maximum value. The reason for this, as well as the possibility of using the LHR noise bands for locating the plasma through position, are discussed.Key words. Magnetospheric physics (plasmasphere; wave propagation)

Scattering of electromagnetic waves by hybrid waves in a two-electron-temperature plasma

1991 ◽  
Vol 46 (1) ◽  
pp. 99-106 ◽  
Author(s):  
S. K. Sharma ◽  
A. Sudarshan
Keyword(s):  
Growth Rate ◽  
Electron Temperature ◽  
High Frequency ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Lower Hybrid ◽  
Stimulated Scattering ◽  
Coupled Modes ◽  
Temperature Plasma ◽  
Electrostatic Perturbation

In this paper, we use the hydrodynamic approach to study the stimulated scattering of high-frequency electromagnetic waves by a low-frequency electrostatic perturbation that is either an upper- or lower-hybrid wave in a two-electron-temperature plasma. Considering the four-wave interaction between a strong high-frequency pump and the low-frequency electrostatic perturbation (LHW or UHW), we obtain the dispersion relation for the scattered wave, which is then solved to obtain an explicit expression for the growth rate of the coupled modes. For a typical Q-machine plasma, results show that in both cases the growth rate increases with noh/noc. This is in contrast with the results of Guha & Asthana (1989), who predicted that, for scattering by a UHW perturbation, the growth rate should decrease with increasing noh/noc.

Aeroacoustic analysis of slat tones

2021 ◽  
Vol 263 (1) ◽  
pp. 5650-5663
Author(s):  
Hasan Kamliya Jawahar ◽  
Syamir Alihan Showkat Ali ◽  
Mahdi Azarpeyvand
Keyword(s):  
Wavelet Transform ◽  
Surface Pressure ◽  
Wavelet Coefficient ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Stream Velocity ◽  
High Lift ◽  
Unsteady Surface Pressure ◽  
Slat Noise ◽  
Generation Mechanisms

Experimental measurements were carried out to assess the aeroacoustic characteristics of a 30P30N high-lift device, with particular attention to slat tonal noise. Three different types of slat modifications, namely slat cove filler, serrated slat cusp, and slat finlets have been experimentally examined. The results are presented for an angle of attack of α = 18 at a free-stream velocity of U = 30 m/s, which corresponds to a chord-based Reynolds number of Re = 7 x 10. The unsteady surface pressure near the slat region and far-field noise were made simultaneously to gain a deeper understanding of the slat noise generation mechanisms. The nature of the low-frequency broadband hump and the slat tones were investigated using higher-order statistical approaches for the baseline 30P30N and modified slat configurations. Continuous wavelet transform of the unsteady surface pressure fluctuations along with secondary wavelet transform of the broadband hump and tones were carried out to analyze the intermittent events induced by the tone generating resonant mechanisms. Stochastic analysis of the wavelet coefficient modulus of the surface pressure fluctuations was also carried out to demonstrate the inherent differences of different tonal frequencies. An understanding into the nature of the noise generated from the slat will help design the new generation of quite high-lift devices.

Wave collapse at the lower‐hybrid resonance

1993 ◽  
Vol 5 (9) ◽  
pp. 3148-3162 ◽  
Author(s):  
V. D. Shapiro ◽  
V. I. Shevchenko ◽  
G. I. Solov’ev ◽  
V. P. Kalinin ◽  
R. Bingham ◽  
...  
Keyword(s):  
Lower Hybrid ◽  
Hybrid Resonance ◽  
Wave Collapse ◽  
Lower Hybrid Resonance
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