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We report observations of co-existing rising and falling tone emissions of electromagnetic ion cyclotron (EMIC) waves by THEMIS E spacecraft. The investigation of these fine structures of the EMIC waves is essential from the point of view of understanding the connection between the proton holes and the proton hills in velocity phase-space. The wave packets of rising and falling tones are tracked by Poynting vector analysis, where we observe that the rising tones are propagating northward and the falling tones are propagating southward. The nonlinear wave growth theory supports our observations. We propose a model where the proton velocity distribution function evolves through the formation of proton holes on the negative side of the distribution function and mirrored resonant protons forming proton hills on the positive side of the distribution function, allowing us to observe the co-existing rising and falling tone EMIC waves. [ABSTRACT FROM AUTHOR]

Quasi electrostatic fluctuations in the upper-hybrid frequency range are commonly detected in the planetary magnetospheric environment. The origin of such phenomena may relate to the instability driven by a loss-cone feature associated with the electrons populating the dipole-like magnetic field. The present paper carries out a one-dimensional electrostatic particle-in-cell simulation accompanied by a reduced quasilinear kinetic theoretical analysis to investigate the dynamics of the upper-hybrid mode instability driven by an initial ring electron distribution function, which is a form of loss-cone distribution. A favorable comparison is found between the two approaches, which shows that the reduced quasilinear theory, which is grounded in the concept of a model of the particle distribution function that is assumed to maintain a fixed mathematical form except that the macroscopic parameters that define the distribution are allowed to evolve in time, can be an effective tool in the study of plasma instabilities, especially if it is guided by and validated against the more rigorous simulation result. [ABSTRACT FROM AUTHOR]

Recent observations have revealed that plasmaspheric hiss consists of many discrete waves called "hiss elements." However, the interaction of energetic electrons (10 keV to several MeV) with the plasmaspheric hiss has only been simulated by the quasilinear (QL) diffusion theory, which does not take the fine wave structure into account. The QL theory cannot address nonlinear particle motions determined by the inhomogeneity factor, which influences the scattering of electrons in pitch angle and energy. This study aims to identify differences between the nonlinear wave–particle interaction and QL theory for plasmaspheric hiss emissions. We conduct test particle simulations to demonstrate the nonlinear interactions between hiss waves and electrons. The nonlinear theory is used to model hiss elements consisting of discrete frequencies and continuous phases. Unlike the other theories, the frequency and amplitude variations in time of the hiss packet are taken into account. Frequencies of the packets are determined to satisfy the separability criterion; when the criterion is met, resonance overlapping is absent, and the electrons can generate each wave element independently. The realistic simulation model of hiss waves reproduces the scattering of electrons by both first- and second-order resonances. We also evaluate the efficiency of electron scattering by calculating nonlinear diffusion coefficients. The diffusion coefficient of equatorial pitch angle is of the same order of magnitude as those calculated by the QL diffusion theory, while we find the effective acceleration of resonant electrons by successive nonlinear trapping, which is not evaluated by the QL theory. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Earth, Planets & Space titled "VLF/ELF remote sensing of ionospheres and magnetospheres." The issue is a result of the 9th VLF/ELF Remote Sensing of Ionospheres and Magnetospheres (VERSIM) Workshop, which took place virtually in November 2020. The workshop focused on studying the behavior of the magnetosphere and ionosphere using Extremely Low Frequency (ELF) and Very Low Frequency (VLF) radio waves. The special issue includes 13 papers on various topics related to VLF/ELF remote sensing, including spacecraft observations, particle simulations, and technical issues. The authors express their gratitude to the reviewers of the articles and declare no competing interests. The guest editors for the special issue are Yoshiharu Omura, Jacob Bortnik, Mark Clilverd, Andrei Demekhov, and Yohei Miyake. [Extracted from the article]

We present Van Allen Probes observations of periodic chorus wave emissions in the troughs of compressional ultralow frequency (ULF) waves. During this event, the spectral gap of chorus waves gradually widens as the spacecraft moves from the equatorial source region towards higher latitudes. Moreover, chorus wave intensity increases and frequency range widens after a substorm injection. We show that the periodic occurrence of chorus waves is attributed to the modulation of threshold amplitude for nonlinear growth of chorus waves by the second spatial derivative of ULF compressional magnetic field. The widening gap can be interpreted in terms of the nonlinear damping mechanism. A good agreement is also found between the nonlinear wave growth theory and the observations regarding the influence of substorm injection on the chorus. These findings support the applicability of the nonlinear theory in describing the chorus wave generation and damping, together with their modulations by ULF waves. Plain Language Summary: In Earth's magnetosphere, plasma waves play a key role in the acceleration, transport, and loss of energetic particles in the Van Allen radiation belts. These waves usually coexist and interact with one another. For example, whistler waves in the kHz range are often modulated by ultralow frequency (ULF) waves in the mHz range, which leads to fascinating phenomena such as pulsating auroral patches. In this paper, we report a representative case study of long‐duration modulation of whistler‐mode chorus emissions by ULF waves, in which chorus waves appear periodically at the trough of the ULF compressional magnetic field. There are two other interesting phenomena including the gradual widening of the chorus wave‐power gap near half of the electron cyclotron frequency and the abrupt enhancement of the chorus wave intensity and frequency range after a substorm injection. We utilize the nonlinear growth theory of chorus emissions to propose, for the first time, that the latitudinal configuration of the compressional ULF waves plays an important role in the modulation process. The nonlinear theory is also used to investigate the effect of substorm injection on chorus emissions and to understand the widening of the wave‐power gap. They both show good agreement with the observations. Key Points: The observed modulation of chorus emissions by ultralow frequency waves is explained in nonlinear theory by the periodic distortion of field configurationThe chorus waves also show a widening gap as the spacecraft moves away from the equator, which agrees with the nonlinear damping scenarioThe intensity and frequency range of the chorus waves increase abruptly due to the substorm injection of energetic electrons [ABSTRACT FROM AUTHOR]

We conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of the background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, the nonlinear process is suppressed. In the simulations, as we enlarge the gradient coefficient of the background magnetic field, waves generated near the equator do not grow through propagation. By examining the range of suitable values of inhomogeneity factor S (i.e., | S | < 2 ), we find the generation of wave packets is limited to the equatorial region when the background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable S values implies that the nonlinear process occurs even at a low level of hot electron density. However, by examining J E that closely relates to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which agrees with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Nonlinear processes associated with the generation process of whistler-mode chorus emissions are summarized. The nonlinear dynamics of energetic electrons interacting with a coherent whistler-mode wave and the formation of electromagnetic electron holes or hills in the velocity phase space are described. The condition for resonant electrons to be free from the anomalous trapping at low pitch angles is obtained. In the presence of the inhomogeneity due to the frequency variation and the gradient of the magnetic field, the electron holes or hills result in resonant currents generating rising-tone emissions or falling-tone emissions, respectively. After formation of a coherent wave at a frequency of the maximum linear growth rate, triggering of the nonlinear wave growth takes place when the wave amplitude is above the threshold amplitude. The wave grows to a level close to the optimum wave amplitude as an absolute instability near the magnetic equator. The nonlinear growth rate at a position away from the equator is derived for a subtracted Maxwellian momentum distribution function with correction to the formulas in the past publications. The triggering process is repeated sequentially at progressively higher frequencies in the case of a rising-tone emission, generating subpackets forming a chorus element. With a higher plasma density as in the plasmasphere, the triggering of subpackets takes place concurrently over a wide range of frequency forming discrete hiss elements with varying frequencies. The mechanism of nonlinear wave damping due to quasi-parallel propagation from the equator is presented, which results in the formation of a gap at half the electron cyclotron frequency, separating a long rising-tone chorus emission into the upper-band and lower-band chorus emissions. The theoretical formulation of an oblique whistler mode wave and its interaction with energetic electrons at the n-th resonance is also presented along with derivation of the inhomogeneity factor. [ABSTRACT FROM AUTHOR]

We conduct test particle simulations to examine the acceleration mechanism of relativistic electrons through interaction with multi-subpacket chorus waves. As the analysis of recent observations reveals, amplitude of a rising tone element of chorus wave consists of many short wave packets. We call this single rising tone chorus element with the collective structure of multiple short wave packets as a multi-subpacket chorus wave. In this simulation, we develop the wave model with rapidly fluctuating amplitude and phase discontinuities across each subpacket, in order to examine how these features of multi-subpacket chorus wave influence the nonlinear trapping processes in efficient acceleration of relativistic electrons such as relativistic turning acceleration (RTA) and ultra-relativistic acceleration (URA). To conduct comprehensive examinations, we test more than nine million particles with various initial conditions covering the energy range from 100 to 6 MeV, and the equatorial pitch angles from 10° to 89°. The test particles interact with a single rising tone element of multi-subpacket chorus wave set up with the maximum amplitude of about 2 nT and the frequency rise from about 1.3 kHz to 3.8 kHz over 0.25 s. Relativistic electrons are accelerated by about 160 keV under preferable conditions. The energy increase verifies the high efficiency of acceleration by the wave–particle interactions, based on the fact that it is achieved by a short time interaction less than 1 s with a single element of chorus wave. By analyzing the detailed behavior of the accelerated electrons, we find successive trapping of the resonant electrons resulting in the efficient accelerations from the consecutive multiple subpackets of a chorus wave element. [ABSTRACT FROM AUTHOR]

We study a novel nonlinear mechanism which could be responsible for the generation of the non-thermal continuum radiation. We propose a mathematical model and perform numerical simulations using 2-D electromagnetic code KEMPO2 to verify the proposed mechanism. In the simulation domain, we have density gradient and ring beam electrons in the dense region as a source of electrostatic (ES) waves through ring-beam instability. These ES waves cause non-gyrotropy of the ring velocity distribution which is necessary for the generation of the harmonic waves. Velocity component vy together with magnetic field Bz of generated Z-mode waves creates Lorentz force in the x-direction (along the magnetic field). Hence, oscillating electrons emit O-mode waves to the low density area. [ABSTRACT FROM AUTHOR]

A 2‐D GCPIC simulation in a dipole field system has been conducted to explore the excitation of oblique whistler mode chorus waves driven by energetic electrons with temperature anisotropy. The rising tone chorus waves are initially generated near the magnetic equator, consisting of a series of subpackets, and become oblique during their propagation. It is found that electron holes in the wave phase space, which are formed due to the nonlinear cyclotron resonance, oscillate in size with time during subpacket formation. The associated inhomogeneity factor varies accordingly, giving rise to various frequency chirping in different phases of subpackets. Distinct nongyrotropic electron distributions are detected in both wave gyrophase and stationary gyrophase. Landau resonance is found to coexist with cyclotron resonance. This study provides multidimensional electron distributions involved in subpacket formation, enabling us to comprehensively understand the nonlinear physics in chorus wave evolution. Plain Language Summary: Subpackets are a series of wave packets within chorus waves, characterized by wave amplitude modulation. In this study, we investigate the electron distributions in various phase spaces associated with subpacket formation, by performing a two‐dimensional simulation in a dipole field. It is found that the electrons can be trapped in the wave phase space through both cyclotron and Landau resonances. These two resonance interactions can also produce the "bump" and "plateau" shapes in momentum space, as well as the fine density structures in spatial space. Therefore, both cyclotron and Landau resonances play an important role in subpacket formation. Our study provides new inspiration for the nonlinear theory of chorus subpackets. Key Points: Oblique chorus subpackets are generated in the 2‐D GCPIC simulation modelElectron hole associated with the inhomogeneity factor oscillates with time during subpacket formationCyclotron and Landau resonances coexist during subpacket formation [ABSTRACT FROM AUTHOR]

This paper presents the wave mode conversion between electrostatic and electromagnetic waves on the plasma density gradient. We use 2-D electromagnetic code KEMPO2 implemented with the generation of density gradient to simulate such a conversion process. In the dense region, we use ring beam instability to generate electron Bernstein waves and we study the temporal evolution of wave spectra, velocity distributions, Poynting flux, and electric and magnetic energies to observe the wave mode conversion. Such a conversion process can be a source of electromagnetic emissions which are routinely measured by spacecraft on the plasmapause density gradient. [ABSTRACT FROM AUTHOR]

We carry out a self-consistent simulation of the generation process of whistler-mode chorus by a spatially one-dimensional electron hybrid code, by assuming the magnetic field inhomogeneity corresponding to L = 4 of the dipole field. Chorus emissions with rising tones are reproduced in the simulation result, while the frequency range, sweep rate, and the amplitude profiles in the spectra of the reproduced elements are consistently explained by the nonlinear wave growth theory. We compare the simulation results with the observation by the Cluster spacecraft (Santolik et al. in J Geophys Res 108:1278, 2003, doi:; Santolik in Nonlinear Process Geophys 15:621-630, 2008) and reveal similarities of the spectral fine structure of reproduced chorus elements with the observation. On the other hand, there is no gap at half the gyrofrequency in the spectra of the reproduced chorus elements, which is evident in the observation. This difference implies that the mechanism of a gap at half the gyrofrequency is governed by the process that is not described by the spatially one-dimensional simulation treating purely parallel propagating electromagnetic waves. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via the original article. [ABSTRACT FROM AUTHOR]

We perform one-dimensional fluid simulation of ion acoustic (IA) solitons propagating parallel to the magnetic field in electron-ion plasmas by assuming a large system length. To model the initial density perturbations (IDP), we employ a KdV soliton type solution. Our simulation demonstrates that the generation mechanism of IA solitons depends on the wavelength of the IDP. The short wavelength IDP evolve into two oppositely propagating identical IA solitons, whereas the long wavelength IDP develop into two indistinguishable chains of multiple IA solitons through a wave breaking process. The wave breaking occurs close to the time when electrostatic energy exceeds half of the kinetic energy of the electron fluid. The wave breaking amplitude and time of its initiation are found to be dependent on characteristics of the IDP. The strength of the IDP controls the number of IA solitons in the solitary chains. The speed, width, and amplitude of IA solitons estimated during their stable propagation in the simulation are in good agreement with the nonlinear fluid theory. This fluid simulation is the first to confirm the validity of the general nonlinear fluid theory, which is widely used in the study of solitary waves in laboratory and space plasmas. [ABSTRACT FROM AUTHOR]

A decomposition scheme was applied to ALOS/PALSAR data obtained from a fast-growing tree plantation in Sumatra, Indonesia to extract tree stem information and then estimate the forest stand volume. The scattering power decomposition of the polarimetric SAR data was performed both with and without a rotation matrix and compared to the following field-measured forest biometric parameters: tree diameter, tree height and stand volume. The analytical results involving the rotation matrix correlated better than those without the rotation matrix even for natural scattering surfaces within the forests. Our primary finding was that all of the decomposition powers from the rotated matrix correlated significantly to the forest biometric parameters when divided by the total power. The surface scattering ratio of the total power markedly decreased with the forest growth, whereas the canopy and double-bounce scattering ratios increased. The observations of the decomposition powers were consistent with the tree growth characteristics. Consequently, we found a significant logarithmic relationship between the decomposition powers and the forest biometric parameters that can potentially be used to estimate the forest stand volume. [ABSTRACT FROM AUTHOR]

Whistler-mode wave–electron interactions constitute an important physical mechanism in the Earth’s magnetosphere and the radiation belts of the magnetized planets. From linear theory, an analytical result for the growth rate of electromagnetic R-mode (whistler-mode) waves in a relativistic bi-Maxwellian plasma with given temperature anisotropy is obtained. In order to test the linear theory, a one-dimensional self-consistent electromagnetic particle simulation is performed with a newly developed fully relativistic code. A major background component of isotropic cold electrons and a minor component of anisotropic hot electrons in a uniform magnetic field are assumed. Driven by the temperature anisotropy of the hot relativistic electrons, the whistler-mode waves grow initially linearly, and then nonlinearly to a level at which saturation takes place. Saturation occurs due to a combination of nonlinear trapping of resonant electrons and quasilinear relaxation of the temperature anisotropy. The initial wave growth rate obtained from the particle simulation agrees well with the growth rate predicted from linear theory. In order to reduce electrostatic fluctuations and achieve accuracy in the simulation, a large number of superparticles must be used. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The biodiversity loss in Southeast Asia indicates an urgent need for long-term monitoring, which is lacking. Much attention is being directed toward bird diversity monitoring using remote sensing, based on relation to forest structure. However, few studies have utilized space-borne active microwave remote sensing, which has considerable advantages in terms of repetitive observations over tropical areas. Here, we evaluate threatened bird occurrence from L-band satellite data explaining forest structure in Sumatra, Indonesia. First, we identified L-band parameters with strong correlations with the forest layer structure, defined as forest floor, understory, and canopy layers. Then, we analyzed the correlation between threatened bird occurrence and L-band parameters identified as explaining forest structure. The results reveal that several parameters can represent the layers of forest floor, understory, and canopy. Subsequent statistical analysis elucidated that forest-dependent and threatened bird species exhibit significant positive correlations with the selected L-band parameters explaining forest floor and understory. Our results highlight the potential of applying microwave satellite remote sensing to evaluate bird diversity through forest structure estimation, although a more comprehensive study is needed to strengthen our findings. [ABSTRACT FROM AUTHOR]

Mercury has a large loss cone difference in its two hemispheres due to the northward shifted magnetic dipole. The precipitation difference of energetic electrons in both hemispheres is poorly understood. We show that the northern precipitation is 2.5‐times higher than for a symmetric loss cone due to the effects of the enhanced whistler instability at the southern hemisphere with the larger loss cone. Simulations including nonlinear pitch angle scattering by the whistler‐mode waves show rapid (tens of milliseconds) electron flux modulation related to the wave subpacket structures by repeated interactions within a discrete wave element. The difference in the nonlinear whistler instability in the two hemispheres should enhance the electron precipitation, which, along with the direct impact effects of solar wind, contributes to Mercury's surface–magnetosphere coupling. Electrons hitting the planet's surface may be a possible factor in the formation of water through the formation of hydroxyl groups. Plain Language Summary: Mercury, the first planet from the Sun, has north–south asymmetric magnetic fields due to the northward shifted magnetic dipole from the planet's center. Computer simulations of plasma waves and electrons, taking into account Mercury's magnetic dipole offset, show that the northward precipitation of electrons is 2.5‐times higher than in the case of no magnetic dipole offset, which is the case like the Earth. This difference in electron precipitation fraction arises from a difference in the characteristics of wave growth due to the spatial characteristics of the planet's magnetic field, because plasma waves can efficiently push trapped electrons in Mercury's magnetosphere toward the planet's surface. This study contributes to the understanding of the electron precipitation fraction on Mercury and may help to estimate the production of water ice through the formation of hydroxyl groups not only by the direct impact of solar wind but also by the electron precipitation caused by plasma waves. Key Points: Whistler‐driven electrons at Mercury are simulated, as the electron precipitation on the planet surface may contribute to water productionFor an asymmetric (southward wider) loss cone, the northward precipitation fraction is 2.5‐times higher than for a symmetric loss coneRapid (tens of milliseconds) electron flux modulations can be observed as a signature of repeated interactions with wave subpackets [ABSTRACT FROM AUTHOR]

Nonlinear gyroresonant acceleration is an essential mechanism for the formation of relativistic electrons in Earth's radiation belts, yet we still have only limited knowledge of how electron motion interacts nonlinearly with plasma waves. Here we demonstrate the compelling suppression of whistler‐mode chorus emissions as a resonant wave with energetic electrons by tuning an external transmitter signal in space plasmas. Through forcible modification of electron motions via phase trapping by the external waves, the nonlinear gyroresonant current is suppressed along with the electron hole deformation. Moreover, this can decrease the population of relativistic electrons due to the lack of coherent resonant waves seen by the phase‐organized electrons. Understanding such nonlinear wave suppression effects is crucial for a potential active control of Earth's plasma environment. Plain Language Summary: Since the strong radiation in space can cause health risks for astronauts and satellite anomalies of electronics, understanding toward the active control of the particle populations is in increasing demand for sustainable space industry growth. The gyroresonant interactions between energetic electrons and whistler‐mode waves play important roles in the acceleration mechanism of the Earth's radiation belt electrons. We find that transmitter signals as an external wave source in space plasmas can utilize the changing of nonlinear electron motion by stimulating electrons in a phase space. We show that nonlinear whistler mode chorus wave excitation, which is the resonant wave source for energetic electrons, can effectively be suppressed by deforming the shape of electron holes to control resonant currents in the phase space. This mechanism is crucial for understanding the active control of Earth's plasma environments. Key Points: Chorus waves can be suppressed by inhibition of coherent interactions with resonant electrons due to adding external transmitter wavesThe external waves having a different frequency from the maximum linear growth can become incoherent from the point of view of electronsThe external waves can precipitate the seed electrons, then this reduces the anisotropy of particles and hence inhibits wave growth [ABSTRACT FROM AUTHOR]

The terrestrial bow shock is the boundary where supersonic solar wind slows down abruptly near the magnetopause. The shock front geometry could be modulated by surface waves to form rippled structures, which impact the acceleration process of the solar wind particles. However, the rippled structures are hard to be identified unambiguously due to the similar signatures in single‐spacecraft observations between rippled shocks and reforming shocks. Here, we utilize the four‐spacecraft observations from the MMS mission to investigate an event of quasi‐perpendicular bow shock crossing. The periodic oscillations of shock normal directions and normal velocities support the scenario of surface wave propagation in the tangential direction. We also reconstruct the shock profile along the normal direction, and its monotonic shape further excludes the occurrence of shock reformation. These ripples are found to modulate the reflected ions and whistler wave packets, which adds to the complexity of the bow shock plasma environments. Plain Language Summary: Collisionless shocks are ubiquitous structures in the space and astrophysical plasma environments where significant energy conversion occurs between electromagnetic energy, kinetic energy, and thermal energy. These structures often exhibit nonstationary signatures, from which important information on the associated plasma dynamics can be extracted. In this paper, we report the spacecraft observations of a bow shock crossing with periodic enhancements of the magnetic field strength. Such signatures have been previously attributed either to the rippled shock structures or to the shock reformation process. These two potential processes are examined via simultaneous observations at four different locations, which shows the periodic oscillations of the local shock normal directions indicative of rippled rather than reforming shocks. We also show that the rippled shocks could spatially modulate the reflected ions and whistler wave packets, so they can also be detected periodically by the spacecraft. This phenomenon has been reported on other planets across a wide range of Mach numbers, indicating that the shock ripples, universal in the plasma universe, play a critical role in impacting particle dynamics and shock evolution processes. Key Points: Periodic magnetic strength enhancements are observed during the bow shock crossing of the MMS spacecraftMulti‐spacecraft analysis supports the scenario of shock ripples rather than the shock reformation processThe surface waves alter the shock geometry, modulating the reflected ions and whistler wave packets [ABSTRACT FROM AUTHOR]

When the electromagnetic environment of the space plasmas observed by a spacecraft in space it is often difficult to distinguish the disturbance due to the satellite itself and natural phenomena. In such cases, it is effective to use a numerical experiment in which the phenomena arising around a spacecraft are reconstructed on a computer. Since the plasma filling the space is extremely dilute, the particles are in a conclusionless condition. To treat such a collisionless plasma, the electrons and ions comprising the plasma are treated as individual particles. In such cases, it is a good approach to use the electro- magnetic particle code in which the electric field and the magnetic field are solved progressively in time according to Maxwell's equations. To reconstruct on the computer, the environment around the spacecraft flying in space as closely as possible, the authors axe developing the electromagnetic particle code in which the spacecraft is included as an internal boundary. This paper reports the numerical experimental results on the electromagnetic environment around the satellite which is formed when the spacecraft is exposed to & high-speed plains flow in a space plasmas. A plasma flow is given from one end of the free boundary, and a spacecraft is placed in such a flow. By changing the parameters of the plasma, the physical quantities controlling the generation of the disturbance axe found. In regard to the mechanism of the disturbance generation and the two-dimensional configuration of the disturbance, several characteristics different from those predicted are obtained. [ABSTRACT FROM AUTHOR]

We perform an electromagnetic particle simulation of triggered emissions in a uniform magnetic field for understanding of nonlinear wave–particle interaction in the vicinity of the magnetic equator. A finite length of a whistler-mode triggering wave packet with a constant frequency is injected by oscillating an external current at the equator. We find that the first subpacket of triggered emissions is generated in the homogeneous magnetic field. By analyzing resonant currents and resonant electron dynamics in the simulation, we find that the formation of an electron hole in a velocity phase space results in resonant currents, and the currents cause wave amplification and frequency increase. We obtain the interaction time of counter-streaming resonant electrons in a triggering wave packet with a finite width. By changing the duration time of the triggering pulse, we evaluate the interaction time necessary for formation of an electron hole. We conduct 4 runs with different duration times of the triggering pulse, 980, 230, 105, 40 Ω e - 1 , which correspond to cases with interaction times, 370%, 86%, 39%, and 15% of the nonlinear trapping period, respectively. We find generation of triggered emissions in the three cases of 370%, 86%, and 39%, which agrees with the conventional nonlinear model that the nonlinear transition time, which is necessary for formation of resonant currents, is about a quarter of the nonlinear trapping period. [ABSTRACT FROM AUTHOR]

Chorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two‐dimensional particle‐in‐cell simulations to investigate self‐consistent wave‐particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase‐trapped cyclotron resonant electrons satisfy the second‐order resonance condition and gain energy from waves. While phase‐bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave‐particle interactions. Plain Language Summary: Wave‐particle interactions can modulate electron distributions through advection and diffusion. Previous studies focusing on advection and diffusion primarily relied on test particle simulations, which uses a simplified model of wave evolution. In this study, we perform self‐consistent simulations to investigate the wave‐particle interactions with chorus waves and quantify the advection and diffusion coefficients of resonant electrons. It is found that advection coefficients are greater than diffusion coefficients in both cyclotron and Landau resonances, indicating the significant role of nonlinear wave‐particle interactions. The quantification of advection and diffusion coefficients in a self‐consistent system is important for understanding and predicting the loss and energization processes in radiation belt electrons. This study complements previous diffusion models that regarded the evolution of electron dynamics in wave‐particle interactions as a slow diffusive process. Key Points: Electron advection and diffusion in wave‐particle interactions with chorus waves are investigated through self‐consistent simulationsThe second‐order time derivative of gyrophase angle is nearly zero for phase‐trapped electrons but is negative for phase‐bunched electronsThe advection and diffusion coefficients for cyclotron and Landau resonant electrons interacting with chorus waves are quantified [ABSTRACT FROM AUTHOR]

Van Allen Probes in situ observations are used to examine detailed subpacket structure observed in strong VLF (very low frequency) rising-tone chorus elements observed at the time of a rapid MeV electron energization in the inner magnetosphere. Analysis of the frequency gap between lower and upper chorus-band waves identifies fceEQ, the electron gyrofrequency in the equatorial wave generation region. Initial subpackets in these strong chorus rising-tone elements begin at a frequency near 1/4 fceEQ and exhibit smooth gradual frequency increase across their > 10 ms temporal duration. A second much stronger subpacket is seen at frequencies around the local value of 1/4 fce with small wave normal angle (< 10°) and steeply rising df/dt. Smooth frequency and phase variation across and between the initial subpackets support continuous phase trapping of resonant electrons and increased potential for MeV electron acceleration. The total energy gain for individual seed electrons with energies between 100 keV and 3 MeV ranges between 2 and 15%, in their nonlinear interaction with a single chorus element. [ABSTRACT FROM AUTHOR]

Chorus subpackets are the wave packets with modulated amplitudes in chorus waves, commonly observed in the magnetospheres of Earth and other planets. Nonlinear wave‐particle interactions have been suggested to play an important role in subpacket formation, yet the corresponding electron dynamics remain not fully understood. In this study, we have investigated the electron trapping through cyclotron resonance with subpackets, using a self‐consistent general curvilinear plasma simulation code simulation model in dipole fields. The electron trapping period has been quantified separately through electron dynamic analysis and theoretical derivation. Both methods indicate that the electron trapping period is shorter than the subpacket period/duration. We have further established the relation between electron trapping period and subpacket period through statistical analysis using simulation and observational data. Our study demonstrates that the nonlinear electron trapping through cyclotron resonance is the dominant mechanism responsible for subpacket formation. Plain Language Summary: The spectrum of chorus waves comprises a series of subpackets, characterized by modulated amplitudes within a timescale of ∼10–100 milliseconds. In this study, we have investigated the self‐consistent wave‐particle interactions with subpackets, using two‐dimensional particle‐in‐cell simulations in dipole fields. Cyclotron resonant electrons are trapped in wave phases, and we have measured their trapping period. Since these electrons move in the opposite direction of subpacket propagation, the corresponding trapping period is smaller than the period of subpackets. We have further established the relation between the two periods and validated it through both simulation and observational data. This relation facilitates evaluating electron trapping period from direct measurement of subpackets in observations. Our study sheds important lights on the key role of nonlinear electron trapping through cyclotron resonance in the formation of subpackets. Key Points: Electron trapping dynamics in the formation of quasi‐parallel chorus subpackets have been investigatedThe linkage between electron trapping period and subpacket period is quantified via a geometric relation, where the trapping period is shorterThe proposed relation between electron trapping period and subpacket period is an extension of the classical results of O'Neil (1965) [ABSTRACT FROM AUTHOR]

We study the nonlinear dynamics of resonant particles interacting with coherent waves in space plasmas. Magnetospheric plasma waves such as whistler-mode chorus, electromagnetic ion cyclotron waves, and hiss emissions contain coherent wave structures with various discrete frequencies. Although these waves are electromagnetic, their interaction with resonant particles can be approximated by equations of motion for a charged particle in a one-dimensional electrostatic wave. The equations are expressed in the form of nonlinear pendulum equations. We perform test particle simulations of electrons in an electrostatic model with Langmuir waves and a non-oscillatory electric field. We solve equations of motion and study the dynamics of particles with different values of inhomogeneity factor S defined as a ratio of the non-oscillatory electric field intensity to the wave amplitude. The simulation results demonstrate deceleration/acceleration, thermalization, and trapping of particles through resonance with a single wave, two waves, and multiple waves. For two-wave and multiple-wave cases, we describe the wave-particle interaction as either coherent or incoherent based on the probability of nonlinear trapping. [ABSTRACT FROM AUTHOR]

Chorus subpackets/subelements are the wave packets occurring at intervals of ∼10–100 msec and are suggested to play a crucial role in the formation of substructures within pulsating aurora. In this study, we investigate the evolution of subpackets from the upstream to downstream regions. Using Van Allen Probe A measurements, we have found that the frequency of the upstream subpackets increases smoothly, but that of the downstream subpackets remains almost unchanged. Through a simulation in the real‐size magnetosphere, we have reproduced the subpackets with characteristics similar to those in observations, and revealed that the frequency chirping is influenced by both resonant current of electrons and wave amplitude due to nonlinear physics. Although the resonant currents in the upstream and downstream regions are comparable, the wave amplitude increases significantly during evolution, resulting in lower sweep rate in the downstream region. Our findings provide a fresh insight into the evolution of chorus subpackets. Plain Language Summary: Subpackets within chorus waves are suggested to play a significant role in producing the substructures within pulsating aurora. How does the frequency change inside subpackets is still an open question. In this study, the subpackets are found with Van Allen Probe A observation to be excited upstream of the magnetic equator, and propagate toward downstream. The frequency of subpackets increases with time in the upstream region, while it keeps almost unchanged in the downstream region. Meanwhile, a particle‐in‐cell simulation has been performed to study the characteristics of subpackets, and the simulation results agree well with those in observations. The frequency variation of subpackets is influenced by both resonant electrons and wave amplitude. Our study provides a clue for better understanding the nonlinear wave‐particle interactions in the evolution of chorus subpackets. Key Points: The source region of chorus subpackets has been observed by Van Allen Probe AThe chorus subpackets have been investigated via the general curvilinear particle‐in‐cell simulation in the real‐size magnetosphereNonlinear physics is a dominant process in the evolution of chorus subpackets [ABSTRACT FROM AUTHOR]

Abstract: In Earth's inner magnetosphere, electromagnetic waves in the ultralow frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift resonance theory, linearization is applied under the assumption of weak wave‐particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here we extend the drift resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a wave‐carried potential well, and predict the corresponding observable signatures such as rolled‐up structures in particle energy spectrum. After considering how this manifests in particle data with finite energy resolution, we compare the predicted signatures with Van Allen Probes observations. Their good agreement provides the first observational evidence for the occurrence of nonlinear drift resonance, highlighting the importance of nonlinear effects in magnetospheric particle dynamics under ULF waves. [ABSTRACT FROM AUTHOR]

The frequency chirping of chorus waves is commonly observed in the Earth's inner magnetosphere, but its generation remains an open question. Recently, Liu et al. (2021), https://doi.org/10.1029/2021JA029258 reported two unusual rising‐tone (upward chirping) chorus elements. Although the central frequency of constituent subpackets rises, the frequency of a single subpacket is surprisingly downward chirping. With a gcPIC‐δf $\delta f$ simulation in the dipole field, we successfully reproduce this kind of substructure, which contains alternating signs of chirping. Interestingly, both hole and hill structures are formed around the theoretical resonant velocities in the electron phase space, no matter whether the chirping is upward or downward. However, during each chirping interval, only one structure (either a hole or a hill) is associated with wave excitation: the upward chirping is related to the hole, while the hill contributes to the downward chirping. Our study provides a fresh perspective on the theory of frequency chirping in chorus waves. Plain Language Summary: The frequency chirping is a typical feature of chorus waves in the Earth's inner magnetosphere, which generally contain either rising‐tone (upward chirping) elements or falling‐tone (downward chirping) elements. Previous theory has suggested that the chirping is due to the nonlinear wave‐particle interaction, where the hole or hill structure is formed in the electron phase space. Recently, Liu et al. (2021), https://doi.org/10.1029/2021JA029258 have observed the upward chirping elements with their subpackets of downward chirping. What electron structure is associated with these elements becomes a puzzle. With a one‐dimensional (1D) general curvilinear particle‐in‐cell (gcPIC) δf simulation in the dipole magnetic field, we successfully reproduce this kind of chorus element, whose frequency contains alternating upward and downward chirping. Interestingly, both the hole and hill structures are formed during a chirping interval, but only one of the two structures is responsible for wave excitation and frequency chirping. The structure of hole‐hill combination provides an important clue into the theory of the frequency chirping in chorus waves. Key Points: With a gcPIC‐δf $\delta f$ simulation in the dipole field, we reproduce the upward chirping chorus element, whose subpackets are downward chirpingBoth hole and hill structures can be formed in the ζ−v‖ $\zeta -{v}_{\Vert }$ phase space, no matter whether the frequency is upward or downward chirpingThe time evolution of the hole and hill structures in the phase space leads to the alternating frequency chirping [ABSTRACT FROM AUTHOR]

Cyclotron resonance between plasma waves and charged particles is a fundamental and ubiquitous process in the plasma universe, during which the particle’s gyromotion has a constant phase in the wave field to enable a sustained energy exchange. In this classical picture, however, the particle’s angular velocity is determined only by the background magnetic field. Here, we show that the classical condition of cyclotron resonance fails to describe the observations of low-energy particles in resonance with large-amplitude waves, which highlights the roles of the wave field in nonlinearly modifying the resonant picture. The revised scenario of anomalous resonance is then validated by the agreement between test-particle simulations and ultrafast spacecraft measurements, which present in-phase and/or antiphase relationships between the wave magnetic field and ion flux oscillations at energy and pitch-angle ranges incompatible with the classical resonance condition. This revision could significantly affect the wave-particle energy exchange and wave evolution processes.The classical picture of cyclotron resonance fails to describe the interaction between large-amplitude plasma waves and low-energy particles. The authors identify anomalous resonance, or nonlinear modification of the classical resonant condition by strong wave field, by ultrafast spacecraft measurements that are consistent with test-particle simulations. [ABSTRACT FROM AUTHOR]

The orbital dynamics of Earth-orbiting solar sails is investigated considering an artificial apse-line precession of an elliptic orbit by solar radiation pressure. The orbital coverage can be flexibly designed for missions such as geomagnetic tail exploration by allowing eccentricity variation via an extremely simple steering law in which the sail normal is set to be directed along the sun line at all times. Equations describing the long-term behavior of eccentricity and argument of perigee are derived by averaging Lagrange's planetary equations constituting a Hamiltonian system. The canonical transformation approach is also shown to yield the same equations. The Hamiltonian of the system makes it possible to investigate the temporal evolution of the eccentricity and the argument of perigee in terms of an eccentricity argument of a perigee phase-space diagram. Orbits in phase space are shown to be classifiable as librational, rotational, or unstable, depending on the magnitude of the characteristic acceleration of the solar sail. The librational dynamics of a solar sail are applied numerically to the case of geomagnetic tail observations. [ABSTRACT FROM AUTHOR]

We present Van Allen Probes observations of a long‐lasting ultralow frequency (ULF) wave event with frequency doubling features in the compressional wave component. The azimuthal magnetic field, on the other hand, shows shoulder‐like pulsations characterized by the presence of two bumps between the crests and troughs within each wave cycle. A wavelet analysis suggests that the shoulder‐like pulsations originate from a secondary peak of the wave power at a frequency of three times the dominant wave frequency. Shoulder‐like pulsations have been observed in many ULF wave events with frequency doubling features, although this phenomenon has never been reported or explained. Here, we propose that these features can be caused by monochromatic oscillations of the magnetic flux tubes in a ballooning‐mirror mode structure. Then, a simple model is developed to reproduce these signatures, which also has the potential to yield uneven bumps in shoulder‐like pulsations depending on the spacecraft location. Plain Language Summary: In Earth's magnetosphere, ultralow frequency (ULF) waves in the mHz frequency range are ubiquitous in space and ground‐based observations. These ULF waves, also referred to as geomagnetic pulsations, play an important role in the dynamic evolution of the magnetosphere by accelerating and transporting charged particles within a wide energy range. An interesting feature that often occurs in long‐lasting ULF waves is oscillation of the compressional magnetic field at twice the frequency of the transverse field oscillations. Moreover, the frequency‐doubling signatures are usually accompanied by shoulder‐like pulsations in the transverse magnetic field, which, in turn, are characterized by the superposition of frequency‐tripled harmonics over the fundamental oscillations such that two bumps appear between the crests and troughs within each wave cycle. In this paper, we report a representative case study of the above signatures based on Van Allen Probes observations. Then, we develop a simple model for examining the origin of these signatures, which indicates that the frequency‐doubling and shoulder‐like pulsations can be simultaneously reproduced by monochromatic oscillations of the magnetic flux tubes in a ballooning‐mirror structure. Key Points: Frequency doubling and shoulder‐like pulsations are observed in compressional and azimuthal magnetic fields, respectively, of Pc5 wavesBoth features are simultaneously reproduced by a model of north/south flux tube oscillations in a ballooning‐mirror structureIn this model, spacecraft off the equator would observe more complicated features due to the coexistence of multiple harmonic variations [ABSTRACT FROM AUTHOR]

We present a statistical study of electromagnetic ion cyclotron (EMIC) waves observed at Antarctic station (geographic 70.7 ∘ S , 11.8 ∘ E , L = 5 ) on quiet and disturbed days during 2011–2017. The data span a fairly good period of both ascending and descending phases of the solar cycle 24, which has witnessed extremely low activity. We noted EMIC wave occurrence by examining wave power in different frequency ranges in the spectrogram. EMIC wave occurrence during ascending and descending phases of solar cycle 24, its local time, seasonal dependence and durations have been examined. There are total 2367 days for which data are available. Overall, EMIC waves are observed for 3166.5 h ( ≈ 5.57 % of total duration) which has contributions from 1263 days. We find a significantly higher EMIC wave occurrence during the descending phase (≈ 6.83%) as compared to the ascending phase (≈ 4.08%) of the solar cycle, which implies nearly a twofold increase in EMIC wave occurrence. This feature is attributed to the higher solar wind dynamic pressure during descending phase of solar activity. There is no evident difference in the percentage occurrence of EMIC waves on magnetically disturbed and quiet days. On ground, EMIC waves show marginally higher occurrence during winter as compared to summer. This seasonal tendency is attributed to lower electron densities and conductivities in the ionosphere, which can affect the propagation of EMIC waves through ionospheric ducts. In local time, the probability distribution function of EMIC wave occurrence shows enhancement during 11.7–20.7 LT (i.e., afternoon–dusk sector). Daily durations of EMIC waves are in the range of 5–1015 min and it is noted that the longer duration (240–1015 min) events are prevalent on quiet days and are mostly seen during the descending phase of solar cycle. [ABSTRACT FROM AUTHOR]

Measurements of plasma parameters and transmitted microwaves are performed in a composite of double-split-ring resonators (DSRRs) making magnetic permeability negative and plasmas excited by a 2.45 GHz microwave. We launch the microwave at 100–200 W, modulated by a pulse wave at a low frequency and a low duty ratio to detect time evolutions of plasma parameters. We perform the measurements at different positions with varying distance from the supporting plate of the DSRRs, and find enhanced wave transmission in the composite with non-uniform profiles of electron temperature. To reinforce the measurements of electron temperature, we evaluate the electron energy distribution function (EEDF) by deriving the second deviation of electron current, upon which data smoothing methods are applied, and the estimated EEDF becomes spatially non-uniform with a similar profile to electron temperature. In terms of the validity of results on the enhanced wave transmission, one-dimensional electromagnetic particle simulations reveal sneaking microwaves inside the composite. In comparison with cases of the negative-permeability and the passive (positive-permeability) DSRRs, we confirm that the non-uniformity is attributed to the magnetic resonance of the DSRRs, which is a microscopic effect of the DSRRs to plasma generation, whereas their macroscopic effect makes permeability negative and enhances wave energy transfer inside the composite. [ABSTRACT FROM AUTHOR]

In the inner magnetosphere, the Arase spacecraft has observed electromagnetic ion cyclotron (EMIC) emissions with both rising and falling frequencies. The instantaneous frequency analyses on the electromagnetic fields of the EMIC rising tone emission have been performed by the Hilbert‐Huang transform. The time variation of the instantaneous frequency shows a good agreement with the nonlinear theory for the frequency evolutions. Rapid instantaneous frequency modulation is also found during the rising tone emission. We estimate the peak‐to‐peak time of the fluctuation in the frequency and find that the fluctuation is caused around a half of the particle trapping time. From the motion of the phase‐bunched particle around the resonant velocity, it is expected that the nonlinear resonant current, which induces the falling frequency is formed in half the trapping time. Plain Language Summary: The Arase spacecraft observed nonlinear EMIC rising and falling tone emissions in the inner magnetosphere. Instantaneous frequency of nonlinear EMIC rising tone emission is analyzed by Hilbert‐Huang Transformation. Fast frequency modulation of the rising tone emission is found in the instantaneous frequency, which can be caused by the phase‐bunched particles in the phase space. Key Points: Typical nonlinear EMIC rising and falling tone emissions have been observed by the electric and magnetic field detectors onboard AraseInstantaneous frequency of a rising tone emission is analyzed and compared with the nonlinear growth theoryEMIC waves have short‐time frequency modulations caused by phase‐bunched ion motion in the phase space [ABSTRACT FROM AUTHOR]

The modes of wave propagation in media with a negative dielectric constant are not simple, unlike those for electromagnetic waves in media with a positive dielectric constant (where modes propagate inside the media with positive phase velocity since the refractive index is usually positive). Instead, they depend on the permeability sign, either positive or negative, and exhibit completely different features. In this report, we investigated a wave confined on the surface of a negative-dielectric-constant and a positive-permeability plasma medium for which the refractive index is imaginary. The propagation mode is similar to surface plasmon polaritons on the metal containing free electrons, but its frequency band is different due to the significant spatial gradient of the dielectric constant and a different pressure term. We also studied a wave with a negative dielectric constant and negative permeability, where the refractive index is negative. This wave can propagate inside the media, but its phase velocity is negative. It also shares similar qualities with waves in plasmonic devices with negative permeability in the photon range. [ABSTRACT FROM AUTHOR]

Electromagnetic plasma waves are thought to be responsible for energy exchange between charged particles in space plasmas. Such an energy exchange process is evidenced by phase space holes identified in the ion distribution function and measurements of the dot product of the plasma wave electric field and the ion velocity. We develop a method to identify ion hole formation, taking into consideration the phase differences between the gyromotion of ions and the electromagnetic ion cyclotron (EMIC) waves. Using this method, we identify ion holes in the distribution function and the resulting nonlinear EMIC wave evolution from Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations. These ion holes are key to wave growth and frequency drift by the ion currents through nonlinear wave-particle interactions, which are identified by a computer simulation in this study. [ABSTRACT FROM AUTHOR]

We examine the growth of magnetospheric whistler-mode waves which comprises a linear growth phase followed by a nonlinear growth phase. We construct time-profiles for the wave amplitude that smoothly match at the transition between linear and nonlinear wave growth. This matching procedure can only take place over a limited 'matching region' in (Nh/N0,AT)-space, where AT is the electron thermal anisotropy, Nh is the hot (energetic) electron number density, and N0 is the cold (background) electron number density. We construct this matching region and determine how the matching wave amplitude varies throughout the region. Further, we specify a boundary in (Nh/N0,AT)-space that separates a region where only linear chorus wave growth can occur from the region in which fully nonlinear chorus growth is possible. We expect that this boundary should prove of practical use in performing computationally expensive full-scale particle simulations, and in interpreting experimental wave data. [ABSTRACT FROM AUTHOR]

Abstract: Our recent observations around the Moon revealed that so-called type-II (T2) entry of the solar wind protons into the near-Moon wake occurs when the IMF is dominated by the non-radial components (i.e. B Y and/or B Z ). Under this condition a part of the solar wind protons scattered/reflected at the lunar dayside surface subsequently enters the central region of the near-Moon wake after a large-scale cycloid motion, which accelerates electrons along the filed line into the wake. The situation handled in the previous studies is that the relevant magnetic field line is detached from the lunar surface, leaving a possibility of the T2 entry under magnetic connection left open. Here we report that the protons can access the central wake region that is magnetically connected to the lunar nightside surface, which we categorize into the T2 entry with magnetic connection to the lunar surface (T2MC). Furthermore we show that the energy of the electron beams induced by the proton entry into the wake depends on the magnetic connectivity. Strong electron acceleration (up to several hundred eV to 1keV) along the magnetic field associated with the T2 entry is prominent when the field line has its both ends in the solar wind, that is, when the magnetic field is detached from the lunar surface (i.e. the previously reported T2 entry that we rename to T2MD). On the other hand, no significant electron acceleration is found in the T2MC cases, although an enhancement of the electron flux associated with the T2 proton entry is evident. We also report that the T2 entry process takes place even under radial (B X -dominated) IMF condition. Our results indicate that, while the T2 entry of solar wind protons into the wake itself does not require a special IMF condition but is a rather general phenomenon, the characteristic energy of associated electrons does show a strong dependence on the magnetic connectivity to the lunar surface. [Copyright &y& Elsevier]

Space development has been rapidly increasing, and a strong demand should arise regarding the understanding of the spacecraft-plasma interactions, which is one of the very important issues associated with the human activities in space. To evaluate the spacecraft-plasma interactions including plasma kinetics, transient process, and electromagnetic field variation, the authors have started to develop a numerical plasma chamber called Geospace Environment Simulator (GES) by making the most use of the conventional full particle-in-cell plasma simulations. For the development of a proto model of GES, the authors have used the Earth Simulator, which is one of the fastest supercomputers in the world. GES can be regarded as a numerical chamber in which space experiments can be virtually performed and temporal and spatial evolutions of spacecraft-plasma interactions can be analyzed. In this paper, the authors have briefly introduced GES in terms of its concept, modeling, and research targets. As one of the research topics of GES, the authors have investigated the impedance variation of electric field antenna onboard scientific satellites in the photoelectron environment in space. From the preliminary simulation results, the large change of reactance of the antenna impedance below the characteristic frequency corresponding to the local plasma frequency determined by the photoelectron density could be confirmed. [ABSTRACT FROM AUTHOR]

The concept of a solar power station (SPS) was proposed 25 years ago. During the intervening years, long-distance, high-power transmission microwave technology has advanced. Realization of wireless power transmission in space is now longer a dream. It is has been predicted from three-way coupling that a static plasma wave is excited when an intense microwave passes through space plasma. The microwave power transmission rocket experiment in a ionosphere in an ionosphere carried out by the author (MINIX, microwave Ionosphere Nonlinear Interaction experiment) has confirmed this fact. In this experiment, a phenomenon that cannot be explained by three wave resonance theory has been discovered. In this paper, a computer experiment using plasma has been carried out with an electromagnetics particles code. Static plasma wave excitation and the saturation Phenomenon are explaned in which not only the simple thee-wave coupling but also the wave-particle interaction are included. [ABSTRACT FROM AUTHOR]

The component wave called the BUM (broad upshifted maximum) excited at the time of electromagnetic heating experiment of the ionosphere is seen on the higher-frequency side band of the pump wave or its harmonics. Therefore, its excitation mechanism cannot be explained by a simple parametric instability. Therefore, the mode instability theory based on the nonuniform density plasma has been proposed. In the present research, in reference to the theoretical prediction as a starting point of analysis of the excitation mechanism, computer experiments are carried out by means of the electromagnetic particle code. It was con- firmed that the density nonuniformity of the plasma is important for the excitation of the BUM. Also, an excitation mechanism of the BUM conceivable from the computer experiment results is proposed. [ABSTRACT FROM AUTHOR]