Numerical study of mode conversion between lower hybrid and whistler waves on short‐scale density striations

Eliasson, Bengt; Papadopoulos, K.

doi:10.1029/2008ja013261

Cited by 35 publications

(59 citation statements)

References 23 publications

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“…A 2D model is used to simulate the interaction of whistler waves with field‐aligned density striations in an inhomogeneous plasma in the presence of collisions. The model is based on decomposition of the electron current density as

{\overset{j}{true}}_{e} = {\overset{j}{true}}_{italicLH} + {\overset{j}{true}}_{W}

and the wave electric field as

\overset{⇀}{E} = {\overset{E}{true}}_{italicLH} + {\overset{E}{true}}_{W}

, where the subscripts LH and W denote “lower hybrid” and “whistler” waves, respectively, and leads to the equations [ Eliasson and Papadopoulos , 2008]:

\frac{\partial {\overset{j}{true}}_{italicLH}}{\partial t} = \nabla^{- 2} \{\frac{e}{m_{e}} \nabla \times [\nabla \times (n_{italicstr} {\overset{E}{true}}_{W} + {\overset{j}{true}}_{italicLH} \times {\overset{B}{true}}_{0})] - \frac{e}{m {}_{i}} \nabla [\nabla \cdot ({\overset{j}{true}}_{italicLH} \times {\overset{B}{true}}_{0})]\} - ν_{italicin} {\overset{j}{true}}_{italicLH}

for the LH waves and to

\frac{\partial {\overset{j}{true}}_{W}}{\partial t} = - \frac{e}{m_{e}} {(1 - λ_{e}^{2} \nabla^{2})}^{- 1} \nabla \times [\nabla \times (λ_{e}^{2} (n_{italicstr} {\overset{E}{true}}_{italicLH} + {\overset{j}{true}}_{W} \times {\overset{B}{true}}_{0} + ν_{italicen} {\overset{j}{true}}_{W}))]

for the whistler waves.…”

Section: Interaction Of Whistler Waves With Density Irregularities Inmentioning

confidence: 99%

Attenuation of whistler waves through conversion to lower hybrid waves in the low‐altitude ionosphere

et al. 2012

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[1] VLF waves excited by powerful ground-based transmitters propagate in the Earth-ionosphere waveguide and leak through the ionosphere to the magnetosphere, where they are often recorded by satellites. Simulations of the propagation of whistler waves using coupled transionospheric VLF propagation and three-dimensional ray-tracing models have shown systematic overestimates of the VLF wavefield strength near 20 kHz in the magnetosphere by about 20 dB in the night and 10 dB during the day. The paper presents numerical simulations of the conversion between whistler and lower hybrid waves interactions in the presence of short-scale field-aligned density irregularities (striations) in Earth's lower ionosphere. The simulations, which incorporate a realistic ionospheric density profile, show that the mode conversion of whistler waves to lower hybrid waves leads to significant attenuation of whistler waves at altitudes between 90 and 150 km. The striation width plays an important role in the conversion efficiency between whistler and lower hybrid wave. Uniformly distributed striations with 8 m transverse size result in 15 dB attenuation in the 90-150 km propagation range, while a spectrum from 2 to 10 m results in 9 dB attenuation. It is argued that the attenuation of whistler waves in the presence of short-scale density striations in Earth's ionosphere can account for most of the observed $20 dB loss in VLF intensity. Furthermore, it predicts that VLF/ELF waves with frequencies below 5 kHz will not suffer similar attenuation.

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{\overset{j}{true}}_{e} = {\overset{j}{true}}_{italicLH} + {\overset{j}{true}}_{W}

and the wave electric field as

\overset{⇀}{E} = {\overset{E}{true}}_{italicLH} + {\overset{E}{true}}_{W}

, where the subscripts LH and W denote “lower hybrid” and “whistler” waves, respectively, and leads to the equations [ Eliasson and Papadopoulos , 2008]:

\frac{\partial {\overset{j}{true}}_{italicLH}}{\partial t} = \nabla^{- 2} \{\frac{e}{m_{e}} \nabla \times [\nabla \times (n_{italicstr} {\overset{E}{true}}_{W} + {\overset{j}{true}}_{italicLH} \times {\overset{B}{true}}_{0})] - \frac{e}{m {}_{i}} \nabla [\nabla \cdot ({\overset{j}{true}}_{italicLH} \times {\overset{B}{true}}_{0})]\} - ν_{italicin} {\overset{j}{true}}_{italicLH}

for the LH waves and to

\frac{\partial {\overset{j}{true}}_{W}}{\partial t} = - \frac{e}{m_{e}} {(1 - λ_{e}^{2} \nabla^{2})}^{- 1} \nabla \times [\nabla \times (λ_{e}^{2} (n_{italicstr} {\overset{E}{true}}_{italicLH} + {\overset{j}{true}}_{W} \times {\overset{B}{true}}_{0} + ν_{italicen} {\overset{j}{true}}_{W}))]

for the whistler waves.…”

Section: Interaction Of Whistler Waves With Density Irregularities Inmentioning

confidence: 99%

Attenuation of whistler waves through conversion to lower hybrid waves in the low‐altitude ionosphere

et al. 2012

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“…Such density depletions can contribute to lower hybrid to whistler mode conversion. [3][4][5] McClements et al 16 also show extended fluctuations along the magnetic field, which they attribute to magnetosonic waves (i.e., k jj d e < k ? d e ( 1) due to a lower hybrid modulational instability, although they did not carry out an analysis of the wave data.…”

Section: Simulation Results At Higher Electron Betamentioning

confidence: 95%

“…Such conversion has been studied recently in the context of the absorption of very low frequency (VLF) waves launched into the ionosphere that convert to whistlers. [3][4][5] This process has also been studied in the laboratory. 6 A second type of interaction involves several different kinds of wave-wave coupling.…”

Section: Introductionmentioning

confidence: 97%

Influence of plasma beta on the generation of lower hybrid and whistler waves by an ion velocity ring distribution

Winske

Daughton

2015

Physics of Plasmas

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We present results of three-dimensional electromagnetic particle-in-cell simulations of the lower hybrid ion ring instability, similar to our earlier results [D. Winske and W. Daughton, Phys. Plasma 19, 072109 (2012)], but at higher electron beta (b e ¼ ratio of electron thermal pressure to magnetic pressure ¼ 0.06, rather than at 0.006) with T i ¼ T e . At higher electron beta, the level of lower hybrid waves at saturation normalized to the ion thermal energy (b i ¼ 0.06 also) is only slightly smaller, but the corresponding magnetic fluctuations are about an order of magnitude larger, consistent with linear theory. After saturation, the waves evolve into whistler waves, through a number of possible mechanisms, with an average growth rate considerably smaller than the linear growth rate of the lower hybrid waves, to a peak fluctuation level that is about 20% above the lower hybrid wave saturation level. The ratio of the peak magnetic fluctuations associated with the whistler waves relative to those of the saturated lower hybrid waves, the ratio of the nonlinear growth rate of whistlers relative to the linear growth rate of lower hybrid waves, the amount of energy extracted from the ring, and the amount of heating of the background ions and electrons are comparable to those in the lower electron beta 3D simulation. This suggests that even at higher electron beta, the linear and nonlinear physics of the lower hybrid ion ring instability is dominated by electrostatic, wave-particle rather than wave-wave interactions.

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“…Based on the proposed mechanism, the observed VLF with frequencies near the LH frequency were generated by resonant mode conversion of LH waves to whistler waves [Eliasson and Papadopoulos, 2008] in the presence of artificially pumped meter-scale striations, as one would expect during long-term CW heating in the case of experiment 1. A simulation of this can be performed by using the LH-whistler mode conversion model developed by Eliasson and Papadopoulos [2008], as shown in Figure 3.10.…”

Section: Generation Of Whistler Waves By Continuous Hf Heating Of Thementioning

confidence: 99%

“…A simulation of this can be performed by using the LH-whistler mode conversion model developed by Eliasson and Papadopoulos [2008], as shown in Figure 3.10. The figure reveals a LH wave packet (Figure 3.10a) interacting with an external field aligned (vertical) striation and generating whistler waves (Figure 3.10b), whose frequency spectrum has a large peak at the LH frequency (Figure 3.10c).…”

Section: Generation Of Whistler Waves By Continuous Hf Heating Of Thementioning

confidence: 99%

Low‐Frequency Waves in HF Heating of the Ionosphere

Sharma¹,

Eliasson²,

Milikh³

et al. 2016

Low‐Frequency Waves in Space Plasmas

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Numerical study of mode conversion between lower hybrid and whistler waves on short‐scale density striations

Cited by 35 publications

References 23 publications

Attenuation of whistler waves through conversion to lower hybrid waves in the low‐altitude ionosphere

Attenuation of whistler waves through conversion to lower hybrid waves in the low‐altitude ionosphere

Influence of plasma beta on the generation of lower hybrid and whistler waves by an ion velocity ring distribution

Low‐Frequency Waves in HF Heating of the Ionosphere

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