Lower Hybrid Drift Research Articles

Lower hybrid and solitary waves in dusk flank region of the Earth’s magnetosphere

A variety of plasma waves have been detected in the vicinity of the magnetopause by various spacecraft missions. In this paper, utilizing high-resolution data from the Magnetospheric Multiscale (MMS) mission, we present new observations of simultaneous lower hybrid and ion solitary waves in the dusk flank region of Earth’s magnetosphere. All four MMS spacecraft consistently observed this wave activity during their traversal from Earth’s magnetosphere to the magnetosheath. Our analysis suggests that the lower hybrid drift waves, driven by lower-hybrid drift instability, were observed in correlation with density gradients. Furthermore, the analysis indicates that the entire ion bulk population drifts, which drives ion solitary waves. It is found that these waves play a crucial role in particle heating in the dusk flank region of Earth’s magnetosphere.

Complete quasilinear model for the acceleration-driven lower hybrid drift instability and a computational assessment of its validity.

A complete quasilinear model is derived for the electrostatic acceleration-driven lower hybrid drift instability in a uniform two-species low-beta plasma in which current is perpendicular to the background magnetic field. The model consists of coupled nonlinear velocity space diffusion equationsfor the volume-averaged ion and electron distribution functions. Each species' diffusion coefficient depends on a time-evolving spectral density of the electric-field energy per unit volume and a time-evolving dispersion relation. The dispersion relation is expressed analytically in integral form without the use of asymptotic limits and applies to arbitrary distribution functions, so long as they can be expressed as a function of one velocity coordinate, e.g., f(v_{y}) or f(v_{⊥}). The quasilinear model conserves energy and is complete in that it fully describes the evolution of the distribution functions, including resonant and nonresonant particle-wave interactions, while accounting for distribution-function-dependent mixed-complex frequencies. The quasilinear diffusion model is solved numerically and self-consistently using a Crank-Nicolson temporal discretization and a second-order finite-volume velocity-space discretization. Numerical solutions are compared to nonlinear fourth-order accurate continuum kinetic Vlasov-Poisson simulations. Evolution of electric-field energy, growth rates, distribution functions, and diffusion coefficients are shown to be in agreement with Vlasov simulations. The quasilinear model is shown to predict anomalous transport terms, like resistivity and heating, to within a factor of order unity. Discrepancies between the quasilinear model and Vlasov simulations are assessed and attributed primarily to lack of damping in the quasilinear description and to the use of unperturbed-orbit susceptibilities in the linear theory dispersion relation. The results illuminate the predictive accuracy of the quasilinear model, place approximate bounds on its validity, and provide much needed vetting of quasilinear theory's ability to predict the nonlinear state of a microturbulent plasma.

Energy Conversion in the Dip Region Preceding Dipolarization Front

AbstractDipolarization fronts (DFs), characterized by sharp increases in the northward magnetic field and usually preceded by magnetic dips, are suggested to play an important role in energy conversion and transport in the magnetotail. It has been documented that strong energy conversion typically develops right at the fronts. Here we present spacecraft observations of electron‐scale energy conversion (EEC) developed inside the dip region ahead of a DF, by using high‐cadence data from the Magnetospheric Multiscale Mission. The EEC, with magnitude comparable to that at the front, is primarily driven by ion current and electron‐scale electric field. The electric field inside the dip is provided by electrostatic waves fed by lower hybrid drift instability, which experiences temporal decaying. Such decaying leads to nonhomogeneity of EEC along the dawn‐dusk direction. These results, uncovering a new channel for DF‐driven energy conversion, can provide important insights into understanding energy transport in the magnetotail.

The lower-hybrid drift instability during the evolution of Kelvin-Helmholtz instability

Abstract The lower-hybrid drift instability (LHDI) is a pivotal phenomenon in astrophysics, playing a critical role in energy transfer, macroscopic structures, and evolutionary processes between the magnetosheath and magnetosphere. Using 2D two-fluids numerical simulation, we investigate the spatiotemporal distribution of LHDI during the evolution of Kelvin-Helmholtz instability (KHI) at Earth’s dusk-flank magnetopause. The numerical simulation results show that, during the linear phase of KHI, the LHDI, whose duration time is approximately ∆t1∼10tA, appears around the high-density arms. During the nonlinear phase of KHI, the LHDI appears around the KH vortexes, with a duration of about ∆t2∼5tA. The LHDI disappears with the decay of KH vortex.

Anomalous Resistivity and Electron Heating by Lower Hybrid Drift Waves during Magnetic Reconnection with a Guide Field.

The lower hybrid drift wave (LHDW) has been a candidate for anomalous resistivity and electron heating inside the electron diffusion region of magnetic reconnection. In a laboratory reconnection layer with a finite guide field, quasielectrostatic LHDW (ES-LHDW) propagating along the direction nearly perpendicular to the local magnetic field is excited in the electron diffusion region. ES-LHDW generates large density fluctuations (δn_{e}, about 25% of the mean density) that are correlated with fluctuations in the out-of-plane electric field (δE_{Y}, about twice larger than the mean reconnection electric field). With a small phase difference (∼30°) between two fluctuating quantities, the anomalous resistivity associated with the observed ES-LHDW is twice larger than the classical resistivity and accounts for 20% of the mean reconnection electric field. After we verify the linear relationship between δn_{e} and δE_{Y}, anomalous electron heating by LHDW is estimated by a quasilinear analysis. The estimated electron heating is about 2.6±0.3 MW/m^{3}, which exceeds the classical Ohmic heating of about 2.0±0.2 MW/m^{3}. This LHDW-driven heating is consistent with the observed trend of higher electron temperatures when the wave amplitude is larger. Presented results provide the first direct estimate of anomalous resistivity and electron heating power by LHDW, which demonstrates the importance of wave-particle interactions in magnetic reconnection.

Instability of Ion Cyclotron Waves (ICWS) at the Expense of Lower Hybrid Drift Waves (LHDWS) Turbulence Energy

Instability of ion cyclotron waves(ICWs) is investigated in presence of lower hybrid drift waves(LHDWs) turbulence. Plasma inhomogeneity in the Earth’s magnetopause region supports a range of low frequency drift wave turbulent fields due to gradients in density in different regions of the media. One of these drift phenomena is identified as lower hybrid drift waves (LHDWs) which satisfies resonant conditions ω − k · v = 0. We have considered a nonlinear wave-particle interaction model where the resonant wave that accelerates the particle in magnetopause may transfer its energy to ion cyclotron waves through a modulated field. In spite of the frequency gaps between the two waves, energy can be transferred nonlinearly to generate unstable ion cyclotron waves which always do not satisfy the resonant condition Ω−K · v ≠ 0 and the nonlinear scattering condition Ω − ω − (K − k) · v ̸= 0. Here, ω and Ω are frequencies of the resonant and the nonresonant waves respectively and k and K are the corresponding wave numbers. We have obtained a nonlinear dispersion relation for ion cyclotron waves(ICWs) in presence of lower hybrid drift waves(LHDWs)turbulence. The growth rate of the ion cyclotron waves using space observational data in the magnetopause region has been estimated.

Successive Energy Conversion at a Stepwise Dipolarization Front

Dipolarization fronts (DFs), ion-scale magnetic structures characterized by sharp enhancement of northward magnetic field developed within plasma jets, have been suggested to play a crucial role in the energy transfer chain in the terrestrial magnetotail. Here we present the first observation of successive energy conversion driven by multiple current layers at a stepwise DF, using high-cadence measurements from NASA’s Magnetospheric Multiscale mission. The multiple current layers are adjacent and cause gradual variations of particles and electromagnetic fields, leading to an intense, successive increase of energy conversion rates at the DF in the satellite frame, with electromagnetic field energy being transformed into particle energy. The energy conversion is contributed by both ion and electron currents. The motional electric field drives the energy conversion, while the wave electric field fed by lower hybrid drift instability modulates the energy partition. These results provide new insights into understanding energy transfer in the terrestrial magnetotail.

3D simulation of lower-hybrid drift waves in strong guide field asymmetric reconnection in laboratory experiments

The magnetic reconnection experiment has recently seen short wavelength ( k ρ e ∼ 1) lower-hybrid waves near the electron diffusion region in strong guide field reconnection. Based on plasma parameters from the experiment, we perform a three-dimensional fully kinetic simulation in order to investigate the generation of the lower-hybrid waves and their effects on the reconnection process. We find that the low-beta regions around the reconnection site are unstable to the lower-hybrid drift instability propagating in the outflow direction, driven by the difference between the electron and ion outflows. The waves modify the electron distributions, leading to periodic opening and closing of gaps in electron velocity space, and provide a small contribution to the anomalous resistivity. Finally, the simulation results are discussed in the context of space observations and laboratory experiments.

Lower Hybrid Waves in High Altitude Echoes of the Topside Equatorial Ionosphere

AbstractWe investigate the mechanism underlying lower hybrid waves associated with high altitude echoes recently detected in the post‐sunset equatorial topside ionosphere and inner plasmasphere by the Jicamarca VHF radar. These waves are visible as prominent sidebands in the echo Doppler spectra. New experimental results and newly processed incoherent scatter radar (ISR) datasets are presented that provide clues as to the conditions in which the echoes and associated waves occur. Numerical simulations are presented which demonstrate the feasibility of an inverse energy cascade coupled with a short wavelength instability, that is, the lower hybrid drift instability, in explaining the waves. An inverse cascade is required for short wavelength lower hybrid waves to extend to the 3 m wavelengths measured by the Jicamarca radar. The simulations were able to reproduce some features of the measurements including the lower hybrid sidebands at 3 m wavelengths, asymmetry in the sidebands, and the damping effect of higher densities and lower altitudes.

Dataset for "3D simulations of lower-hybrid drift waves in strong guide field asymmetric reconnection in laboratory experiments"

Dataset for "3D simulations of lower-hybrid drift waves in strong guide field asymmetric reconnection in laboratory experiments"

In Situ Observations of Lower Hybrid Drift Waves at the Inner Edge of the Ring Current by the Van Allen Probe‐A

AbstractIn the magnetosphere of the Earth, lower hybrid drift (LHD) waves effectively cause plasma diffusion and couple well to both electrons and ions. LHD waves have the characteristics of linear polarization and highly oblique propagation with frequencies near the lower hybrid resonance frequency, which is similar to the characteristics of high‐frequency magnetosonic (MS) waves. The existence of diamagnetic drift at the inner edge of the ring current provides free energy for the excitation of LHD waves, while the free energy to generate MS waves are provided by proton ring distribution. Here, we report on a typical case of LHD waves which was excited by LHD instability. Different from the global distribution of high‐frequency MS waves, statistical results indicate that most LHD waves have a uniform distribution over all MLTs except the noon sector inside the plasmapause. Besides, the occurrence of LHD waves reaches a maximum in the dusk sector outside the plasmapause.

Thermal instabilities in micropinches under turbulent heating conditions

Anomalous thermal (AT) instabilities occurring in micropinches are analyzed based on the theory of small perturbations. Instabilities of this type develop in a high-temperature plasma under turbulent heating conditions in the presence of an anomalous resistance resulting from the scattering of electrons by lower hybrid drift oscillations. When turbulent heating occurs in the plasma of a micropinch, its resistivity increases with decreasing density; this may lead to the formation of plasma layers normal to the current flow (stratification). For the AT instability, a dispersion relation taking into account the effect of the plasma self-radiation has been derived, and the characteristic instability growth rates and wavelengths have been determined. A comparison of the development pattern has been performed between AT and sausage-type magnetohydrodynamic instabilities. It has been shown that for any pinch material, there is a threshold current below which AT instabilities prevail over magnetohydrodynamic instabilities. For the metals considered (aluminum, titanium, copper, molybdenum, and tungsten), the threshold currents are hundreds of kiloamperes. The threshold current increases with atomic number: for tungsten, it is approximately 3.5 times higher than for aluminum. The conclusions drawn from the analysis based on the linear small perturbation theory are compared with the results of experiments in which the parameters of ‘hot spots’ formed in X pinches were determined.

First Observation of Lower Hybrid Drift Waves at the Edge of the Current Sheet in the Martian Magnetotail

Lower hybrid drift waves are commonly observed at plasma boundaries, playing an important role in plasma dynamics. Such waves have been widely investigated in the terrestrial magnetosphere but have never been reported in other planetary environments. Here, using the measurements from the Mars Atmosphere and Volatile EvolutioN mission, we present the first observation of electromagnetic lower hybrid drift waves at the edge of the current sheet on the dusk side of the Martian magnetotail, which should be locally excited rather than propagated from other regions. These plasma waves are associated with significant density gradients and magnetic field gradients. Based on the measured local plasma parameters and the sufficient condition for lower hybrid drift instability to be excited, we find that the proton density gradient is sharp enough to excite the lower hybrid drift instability. The analysis of the existence condition for lower hybrid drift instability indicates that these lower hybrid drift waves at the edge of the current sheet are generated through lower hybrid drift instability. The above results can improve our understanding of Mars’ magnetospheric dynamics.

Magnetospheric Multiscale Mission Observations of Lower-hybrid Drift Waves in Terrestrial Magnetotail Reconnection with Moderate Guide Field and Asymmetric Plasma Density

Utilizing high-resolution data from the Magnetospheric Multiscale mission, we present new observations of lower-hybrid drift waves (LHDWs) in terrestrial magnetotail reconnection with guide field levels of ∼70% and asymmetric plasma density (N high/N low ∼ 2.5). The LHDWs, driven by lower-hybrid drift instability, were observed in correlation with magnetic field and density gradients at separatrices on both sides of the reconnection current sheet. The properties of the LHDWs at both sides of the separatrices are different: (1) At high-density side separatrices, the LHDWs with wavelength kρ e ∼ 0.41 propagated away from the X-line mainly in the L–M plane; (2) at the low-density side separatrices, the LHDWs with wavelengths kρ e ∼ 0.76 and kρ e ∼ 0.35 propagated mainly along the outflow direction and current sheet normal. It is also found that the perpendicular magnetic field fluctuations were comparable to the parallel component. Wave potential of the LHDWs was 20% ∼ 35% of the electron temperature. The LHDWs contributed to electron demagnetization and energy dissipation. Our study can promote understanding of properties of LHDWs during magnetic reconnection.

Effect of Two Different Electron Temperatures in Auroral Ionosphere

We have investigated the effect of two different electron temperatures in an auroral ionosphere in the presence of ions and obtained a modified electron-acoustic and modified lower-hybrid drift dissipative modes which will not be affected much due to the presence of cold electrons. However, in the drift dissipative case, the growth rate of the electron-acoustic wave depends on the number density of cold electrons.

Effects of Coulomb collisions on lower hybrid drift waves inside a laboratory reconnection current sheet

We have developed a local, linear theoretical model for lower hybrid drift waves that can be used for plasmas in the weakly collisional regime. Two cases with typical plasma and field parameters for the current sheet of the magnetic reconnection experiment have been studied. For a case with a low electron beta (βe=0.25, high guide field case), the quasi-electrostatic lower hybrid drift wave is unstable, while the electromagnetic lower hybrid drift wave has a positive growth rate for a high-βe case (βe=8.9, low guide field case). For both cases, including the effects of Coulomb collisions reduces the growth rate but collisional impacts on the dispersion and growth rate are limited (≲20%).

Diffusive Plasma Transport by the Magnetopause Kelvin-Helmholtz Instability During Southward IMF

At the Earth’s low-latitude magnetopause, the Kelvin-Helmholtz (KH) waves, which are driven by the super-Alfvénic velocity shear across the magnetopause, have been frequently observed during periods of northward interplanetary-magnetic-field (IMF) and believed to contribute to efficiently transporting the solar wind plasmas into the magnetosphere. On the other hand, during southward IMF periods, the signatures of the KH waves are much less frequently observed and how the KH waves contribute to the solar wind transport has not been well explored. Recently, the Magnetospheric Multiscale (MMS) mission successfully detected signatures of the KH waves near the dusk-flank of the magnetopause during southward IMF. In this study, we analyzed a series of two- and three-dimensional fully kinetic simulations modeling this MMS event. The results show that a turbulent evolution of the lower-hybrid drift instability (LHDI) near the low-density (magnetospheric) side of the edge layer of the KH waves rapidly disturbs the structure of the layer and causes an effective transport of plasmas across the layer. The obtained transport rate is comparable to or even larger than that predicted for the northward IMF. These results indicate that the diffusive solar wind transport induced by the KH waves may be active at the flank-to-tail magnetopause during southward IMF.

Lower hybrid drift wave motion at a dayside magnetopause x-line with energy conversion dominated by a parallel electric field

On December 4, 2017 at approximately 6:15:38 UTC, magnetospheric multiscale (MMS) encountered a reconnecting current sheet near the dayside magnetopause. MMS2 passed through the current sheet just sunward of the southward-moving x-line and observed the crescent-shaped electron velocity distributions associated with reconnection. Additionally, MMS2 observed anti-correlated oscillations in the Hall electric field EN and in the parallel electric field Eǁ at a frequency just below the lower hybrid (LH) frequency. These oscillations appear to be LH drift waves (also called corrugations), which have previously been observed along the dayside magnetopause but were not seen to cause the same kinds of oscillations in the electric field components as observed in this event. It appears that MMS2 periodically crosses a separatrix between the region where EN dominates and a different region where Eǁ dominates at the wave frequency likely due to the wave motion. We also observe energy conversion dominated by Eǁ and veǁ, mostly in the L-direction, in this region as opposed to the reconnection electric field EM and meandering electrons moving in the M-direction as is typically observed during reconnection near an x-line.

Statistical investigation of electric field fluctuations around the lower-hybrid frequency range at dipolarization fronts in the near-earth magnetotail

Dipolarization fronts (DFs) are thin magnetic boundary structures, embedded in short-duration, fast earthward-moving plasma flows, so-called bursty bulk flows. Previous case studies have shown that the density gradient at DFs can excite the lower-hybrid drift instability (LHDI) and resulting kinetic-scale waves. These waves feature strong electric field fluctuations perpendicular to the ambient magnetic field and associated effective particle acceleration/heating. In this study, we statistically examine electric field fluctuations in the lower-hybrid (LH) frequency range of 61 DF events, using data from the Magnetospheric Multiscale (MMS) Mission between 2017 and 2018 when the MMS apogee was in the magnetotail. We observed that all DF events exhibit enhanced power in the electric field fluctuations in the LH frequency range. Among the observed events, the power can vary by several orders of magnitude. The waves are detected for both high and low values of the perpendicular electron density or pressure gradient. In addition, the peak wave power within the DF is often observed at the time of steepest density gradient within the DF. The results also reveal that the wave power correlates with the magnetic flux transport rate of the DFs. These findings suggest that enhanced density and pressure gradients, which can be formed by large-scale flux transport at DFs, lead to LHDI-related kinetic-scale wave signatures at the DFs, and this may modify the original gradient layer profile of the DF in the course of its propagation from the source to the observation point.

Investigation of the homogeneity of energy conversion processes at dipolarization fronts from MMS measurements

We report on six dipolarization fronts (DFs) embedded in fast earthward flows detected by the Magnetospheric Multiscale mission during a substorm event on 23 July 2017. We analyzed Ohm's law for each event and found that ions are mostly decoupled from the magnetic field by Hall fields. However, the electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electron decoupling at DF. We also analyzed the energy conversion process and found that the energy in the spacecraft frame is transferred from the electromagnetic field to the plasma (J·E>0) ahead or at the DF, whereas it is the opposite (J·E<0) behind the front. This reversal is mainly due to a local reversal of the cross-tail current indicating a substructure of the DF. In the fluid frame, we found that the energy is mostly transferred from the plasma to the electromagnetic field (J·E′<0) and should contribute to the deceleration of the fast flow. However, we show that the energy conversion process is not homogeneous at the electron scales due to electric field fluctuations likely related to lower-hybrid drift waves. Our results suggest that the role of DF in the global energy cycle of the magnetosphere still deserves more investigation. In particular, statistical studies on DF are required to be carried out with caution due to these electron scale substructures.