Parametric Interaction of VLF and ELF Waves in the Ionosphere (original) (raw)
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Full wave description of VLF wave penetration through the ionosphere
A VLF wave that propagates in the Earth's plasmasphere in the whistler mode must be converted into free space mode in order to be observed on the ground. This conversion takes place in collisional and highly inhomogeneous ionospheric plasma, which makes the description of the process not easy. Since an understanding of this process is vital for the analysis of VLF data, it has been in the focus of research since the beginning of whistler studies. A general approach to this problem, which is based on Maxwell's equations in magnetized plasma, is well developed and commonly accepted. However, its direct implementation meets serious difficulties which reveal themselves in numerical swamping. The intrinsic reason behind this is the existence of evanescent mode in the whistler frequency band. This leads to exponential growth of numerical solutions to the general set of equations. Various methods that have been developed to suppress this instability shift a solution of the physical problem to the field of simulation skill, so that the essential part of solution remains largely hidden. In this work we develop a new approach to the problem in which the evanescent mode is analytically excluded from consideration, making numerical calculations plain and straightforward. Using this approach, we find the field of whistler mode wave incident on the ionosphere from above in the whole span of altitudes, and calculate the reflection coefficient as a function of frequency for a number of incidence angles. We explain a quasiperiodic behaviour of the reflection coefficient by resonance absorption of the waves in the lower ionosphere.
Nonlinear VLF effects in the topside ionosphere
Geophysical Research Letters, 2010
1] The Demeter satellite observed intense broadband lower-and upper-hybrid electrostatic waves and plasma perturbations associated with high-power whistler-mode signals from the very-low frequency (VLF) transmitter NWC. This paper shows that the Demeter observations can be explained by nonlinear interactions driven by VLF pump waves, thereby suggesting that nonlinear effects are responsible for energy losses of high-power VLF signals in the ionosphere. Citation: Mishin, E. V., M.
Plasma Physics and Controlled Fusion
The concept of a parametric antenna in ionospheric plasma is analyzed. Such antennas are capable of exciting electromagnetic radiation fields, specifically the creation of whistler waves generated at the very low frequency (VLF) range, which are also capable of propagating large distances away from the source region. The mechanism of whistler wave generation is considered a parametric interaction of quasi-electrostatic low oblique resonance (LOR) oscillations excited by 1conventional loop antenna. The transformation of LOR waves on quasi-neutral density perturbations in the near field of an antenna gives rise to whistler waves on combination frequencies. It is shown in this work that the amplitude of these waves can considerably exceed the amplitude of whistler waves directly excited by a loop. Additionally, particle-in-cell (PIC) simulations, which demonstrate the excitation and spatial structure of VLF waves excited by a loop antenna, is presented. Possible applications including the wave-particle interactions to mitigate performance anomalies of Low Earth Orbit (LEO) satellites, active space experiments, communication via VLF waves, and modification experiments in the ionosphere will be discussed.
Space Sciences Series of ISSI, 2011
Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earthionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms.
Journal of Geophysical Research, 2008
During the early phase of the intense magnetic storm of 7-11 November 2004, the DEMETER satellite encountered large-scale equatorial plasma density depletions with density decreases of two or three orders of magnitude. Wave measurements carried out inside these depletions show the occurrence of broadband and localized lower-hybrid turbulence triggered by whistlers propagating from thunderstorm lightning occurring below the orbit path. High-sample-rate waveforms reveal that this lower-hybrid turbulence can evolve into localized large-amplitude quasi-monochromatic wave packets similar to lower-hybrid structures that were, up to now, only observed in the auroral regions, usually on high-latitude magnetic field lines associated with discrete aurora. These equatorial structures have typical amplitudes of up to 20 mV/m and durations of $20-30 ms. Simultaneous thermal ion measurements show that these bursts are often correlated with small-scale density depletions of 5-10%. Although the lower-hybrid structures are less intense than those observed in the auroral zone and although their energy source is different, our observations lend support to the idea that the formation of lower-hybrid structures is an universal mechanism operating in inhomogeneous magnetized space plasmas in the presence of VLF whistler mode turbulence. Besides the lower-hybrid turbulence, another interesting feature is the occurrence of strong narrowband electromagnetic ELF emissions with amplitudes of a few millivolts per meter at frequencies below the proton gyrofrequency. They are continuously observed throughout the entire depletion. These emissions occur not only within the depletions but also, although less intense, outside of them over a large latitudinal range. They are tentatively identified as magnetospheric line radiations (MLRs) commonly observed during magnetically disturbed periods. Similar events were observed on 15 May 2005 and on 24 August 2005 during two other intense magnetic storms.
Nonlinear mechanisms of lower-band and upper-band VLF chorus emissions in the magnetosphere
Journal of Geophysical Research, 2009
1] We develop a nonlinear wave growth theory of magnetospheric chorus emissions, taking into account the spatial inhomogeneity of the static magnetic field and the plasma density variation along the magnetic field line. We derive theoretical expressions for the nonlinear growth rate and the amplitude threshold for the generation of self-sustaining chorus emissions. We assume that nonlinear growth of a whistler mode wave is initiated at the magnetic equator where the linear growth rate maximizes. Self-sustaining emissions become possible when the wave propagates away from the equator during which process the increasing gradients of the static magnetic field and electron density provide the conditions for nonlinear growth. The amplitude threshold is tested against both observational data and self-consistent particle simulations of the chorus emissions. The self-sustaining mechanism can result in a rising tone emission covering the frequency range of 0.1-0.7 W e0 , where W e0 is the equatorial electron gyrofrequency. During propagation, higher frequencies are subject to stronger dispersion effects that can destroy the self-sustaining mechanism. We obtain a pair of coupled differential equations for the wave amplitude and frequency. Solving the equations numerically, we reproduce a rising tone of VLF whistler mode emissions that is continuous in frequency. Chorus emissions, however, characteristically occur in two distinct frequency ranges, a lower band and an upper band, separated at half the electron gyrofrequency. We explain the gap by means of the nonlinear damping of the longitudinal component of a slightly oblique whistler mode wave packet propagating along the inhomogeneous static magnetic field.
Generation of ELF waves during HF heating of the ionosphere at midlatitudes
Radio Science
Modulated high-frequency radio frequency heating of the ionospheric F region produces a local modulation of the electron temperature, and the resulting pressure gradient gives rise to a diamagnetic current. The oscillations of the diamagnetic current excite hydromagnetic waves in the ELF range that propagate away from the heated region. The generation of the waves in the 2-10 Hz range by a modulated heating in the midlatitude ionosphere is studied using numerical simulations of a collisional Hall-magnetohydrodynamic model. To model the plasma processes in the midlatitude ionosphere the Earth's dipole magnetic field and typical ionospheric plasma parameters are used. As the hydromagnetic waves propagate away from the heated region in the F region, the varying plasma conditions lead to changes in their characteristics. Magnetosonic waves generated in the heating region and propagating down to the E region, where the Hall conductivity is dominant, excite oscillating Hall currents that produce shear Alfvén waves propagating along the field lines into the magnetosphere, where they propagate as the electromagnetic ion cyclotron (EMIC) and whistler waves. The EMIC waves propagate to the ion cyclotron resonance layer in the magnetosphere, where they are absorbed.
Science China Earth Sciences, 2010
Interactions between very/extremely low frequency (VLF/ELF) waves and energetic electrons play a fundamental role in dynamics occurring in the inner magnetosphere. Here, we briefly discuss global properties of VLF/ELF waves, along with the variability of the electron radiation belts associated with wave-particle interactions and radial diffusion. We provide cases of electron loss and acceleration as a result of wave-particle interactions primarily due to such waves, and particularly some preliminary results of 3D evolution of phase space density from our currently developing 3D code. We comment on the existing mechanisms responsible for acceleration and loss, and identify several critical issues that need to be addressed. We review latest progress and suggest open questions for future investigation.
Journal of Geophysical Research, 1975
An analysis of ac electric field data obtained on board the OV 1-17 satellite and ac magnetic field data obtained on board the Ogo 6 satellite has been made during the northern hemisphere spring and summer of 1969 with the purpose of studying extreme low frequency (ELF) electromagnetic waves above the earth's ionosphere. The results are in basic agreement with a number of previous ground-based and lowaltitude satellite experiments in that the peak signal was observed at high latitudes outside the statistical location of the plasmapause on the day side of the earth, that ELF chorus was very often observed in conjunction with the steady ELF hiss emissions, that the winter hemisphere signal was considerably smaller than that observed in summer or in equinoctial months, and that the emission strength and region of occurrence are asymmetric about magnetic noon. Observations of such strong hiss signals outside the plasmasphere are somewhat surprising in light of Ogo 3 and Ogo 5 measurements which show steady ELF hiss to be closely confined to theplasmasphere at high altitudes during normal circumstances. The present study supports the hypothesis that hiss leaks out of the plasmasphere and refracts downward into the lower ionosphere; such a model predicts the observed summer-winter asymmetry and the poleward skewing of the ELF peak signal strength with decreasing altitude. The observation reported here that the highlatitude boundary for ELF signals in the ionosphere is very near the low-latitude boundary for longwavelength ionospheric irregularities and, at least in the morning hours, very near the horizontal density gradient due to precipitation of magnetosheath plasma in the cusp suggests that these variations in the medium act to reflect the waves and to increase the high-latitude intensity further. The relationship between signal strength and magnetic activity shown by these data is in agreement with other in situ measurements but not with some ground-based data. It is argued, however, that the anticorrelation observed at high-latitude ground stations is due to an equatorward displacement of the peak wave intensity region with increasing magnetic activity; such an equatorward displacement is shown in our results. It is also shown that a significant component of wave electric field is parallel to the wave number k and hence that Landau resonant effects may occur at low altitudes between outer zone radiation belt particles and ELF hiss. INTRODUCTION Extremely low frequency (ELF) waves in the frequency range from a few hertz to a few kilohertz are the most common, and perhaps the most intense, electromagnetic emission observed in the earth's ionosphere. Such ELF waves were first observed from the ground [