A5041125210- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Earthquake Detection and Analysis
- Magnetic confinement fusion research
- Geomagnetism and Paleomagnetism Studies
- Seismic Waves and Analysis
- Plasma Diagnostics and Applications
- Astro and Planetary Science
- Dust and Plasma Wave Phenomena
- Planetary Science and Exploration
- Particle accelerators and beam dynamics
- Geophysics and Sensor Technology
- Gyrotron and Vacuum Electronics Research
- Lightning and Electromagnetic Phenomena
- GNSS positioning and interference
- Astrophysics and Cosmic Phenomena
- Particle Accelerators and Free-Electron Lasers
- Ocean Waves and Remote Sensing
- Electromagnetic Compatibility and Measurements
- Cold Atom Physics and Bose-Einstein Condensates
- Atomic and Subatomic Physics Research
- Radio Wave Propagation Studies
- Laser-induced spectroscopy and plasma
- Electrostatic Discharge in Electronics
- Underwater Acoustics Research
Kyoto University
2016-2025
Macau University of Science and Technology
2024-2025
Research Institute for Sustainable Humanosphere
2011-2024
Kyoto Bunkyo University
2005-2024
Geological Survey of India
2023-2024
Midnapore Medical College and Hospital
2023
United Nations University Institute for Sustainability and Peace
2014-2022
Japan Aerospace Exploration Agency
2021
Institute of Space and Astronautical Science
2021
Institute for Sustainable Development
2016-2019
Wave forms of BEN (Broadband Electrostatic Noise) in the geomagnetic tail were first detected by Form Capture receiver on GEOTAIL spacecraft. The results show that most plasma sheet boundary layer (PSBL) are not continuous broadband noise but composed a series solitary pulses having special form which we term “Electrostatic Solitary Waves (ESW)”. A nonlinear BGK potential model is proposed as generation mechanism for ESW based upon simple particle simulation considers highly evolution...
The generation process of whistler‐mode chorus emissions is analyzed by both theory and simulation. Driven an assumed strong temperature anisotropy energetic electrons, the initial wave growth linear. After linear phase, amplitude grows nonlinearly. It found that seeds with rising frequency are generated near magnetic equator as a result nonlinear mechanism depends on amplitude. We derive relativistic second‐order resonance condition for varying frequency. Wave trapping resonant electrons...
We develop a nonlinear wave growth theory of magnetospheric chorus emissions, taking into account the spatial inhomogeneity static magnetic field and plasma density variation along line. derive theoretical expressions for rate amplitude threshold generation self‐sustaining emissions. assume that whistler mode is initiated at equator where linear maximizes. Self‐sustaining emissions become possible when propagates away from during which process increasing gradients electron provide conditions...
We present computer experiments of electrostatic solitary waves (ESW) observed by Geotail in the magnetotail. ESW correspond to broadband noise, and they are excited through electron two‐stream instabilities along a static magnetic field. performed one‐dimensional particle simulations involving two beams an ion beam traveling vary density ratio thermal velocities beams. The values these parameters strongly affect diffusion processes beams, accordingly, different types generated. studied four...
We report a very efficient process for accelerating high‐energy electrons by coherent whistler mode waves in the Earth's dipole magnetic field, which we have found our recent test particle simulations. The acceleration takes place weakly relativistic seed of few hundred kiloelectronvolts. Under an assumption that wave packets are excited near equatorial plane inner magnetosphere and propagate away from equator, becomes irreversible. With sufficiently long packet order 1 s, energetic...
A self‐consistent particle simulation with a dipole magnetic field model is carried out, reproducing chorus emissions rising tones successfully. We assume energetic electrons forming highly anisotropic velocity distribution in the equatorial region. No initial wave assumed except for electromagnetic thermal noise induced by electrons. In early stage of simulation, coherent whistler‐mode waves are generated from equator through an instability driven temperature anisotropy During propagation...
The Cluster spacecraft were favorably positioned on the nightside near equatorial plasmapause of Earth at L ∼ 4.3 30 March 2002 to observe electromagnetic ion cyclotron (EMIC) rising tone emissions in association with Pc1 waves 1.5 Hz. EMIC found be left‐hand, circularly polarized, dispersive, and propagating away from equator. Their burstiness dispersion ∼30s/Hz out Hz are consistent their identification as triggered chorus emissions, first reported through situ observations plasmapause....
Abstract Although most studies of the effects electromagnetic ion cyclotron (EMIC) waves on Earth's outer radiation belt have focused events in afternoon sector plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range local times and L shells. We present here observations event 23 February 2014 that extended over 8 h UT 12 time, stimulated by gradual 4 rise subsequent sharp increases solar wind pressure....
[1] Chorus emissions are triggered from the linear cyclotron instability driven by temperature anisotropy of energetic electrons (10–100 keV) in magnetosphere. Chorus grow as an absolute nonlinear near magnetic equator because presence electromagnetic electron hole velocity space. The transition process wave growth at a constant frequency to with rising tone is due formation resonant current −JB antiparallel field. rising-tone introduces phase shift and results component electric field −JE,...
We derive the second‐order resonance condition for interaction between a relativistic electron and coherent Electromagnetic Ion Cyclotron (EMIC) wave with variable frequency. perform test particle simulations of electrons interacting EMIC waves fixed frequency rising‐tone such as triggered emissions observed in inner magnetosphere. Trapping resonant leads to rapid efficient pitch angle scattering electrons, resulting bursty precipitation electrons. The efficiency depends on gradient magnetic...
Abstract We perform test particle simulations of energetic electrons interacting with whistler mode chorus emissions. compute trajectories a large number forming delta function the same energy and equatorial pitch angle. The are launched at different locations along magnetic field line timings respect to pair emissions generated equator. follow evolution obtain distribution in angle, which is numerical Green's for one cycle wave‐particle interaction. functions range 10 keV–6 MeV all angles...
By a series of self‐consistent electron hybrid code simulations, we study the effect background magnetic field inhomogeneity on generation process whistler‐mode chorus emissions. Chorus with rising tones are generated through nonlinear wave‐particle interactions occurring around equator. The mirror force plays an important role in interactions, and spatial is key parameter process. We have conducted numerical experiments different inhomogeneities to understand properties assume same initial...
Abstract Prompt recovery of MeV (millions electron Volts) populations in the poststorm core outer terrestrial radiation belt involves local acceleration a seed population energetic electrons interactions with VLF chorus waves. Electron during generation rising tones are strongly nonlinear, such that fraction relativistic at resonant energies trapped by waves, leading to significant nonadiabatic energy exchange. Through detailed examination and fluxes observed Van Allen Probes, we investigate...
Abstract Nonlinear processes associated with the generation process of whistler-mode chorus emissions are summarized. The nonlinear dynamics energetic electrons interacting a coherent wave and formation electromagnetic electron holes or hills in velocity phase space described. condition for resonant to be free from anomalous trapping at low pitch angles is obtained. In presence inhomogeneity due frequency variation gradient magnetic field, result currents generating rising-tone falling-tone...
Abstract 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 are initially generated near magnetic equator, consisting series subpackets, and become during their propagation. It is found that electron holes wave phase space, which formed due nonlinear cyclotron resonance, oscillate size time subpacket formation. associated inhomogeneity...
The Geotail satellite skims the dayside magnetosphere in equatorial region at about L = 10. During such passes WFC (Waveform Capture Receiver) observes VLF chorus and discrete emissions band 200 ∼ 1200 Hz. most common waveforms observed are rising tones chorus, with hooks fallers being seen occasionally. Analysis shows that k vectors closely parallel to ambient magnetic field. has available comprehensive wave particle data vicinity of generation regions emissions. A well‐established Vlasov...
We present simulations of the electrostatic solitary waves (ESW) as observed by GEOTAIL which have been identified broadband noise (BEN) in previous studies. found that ESW are generated a result nonlinear coalescence strong excited an beam instability. This instability is driven electron drifting relative to ions and other electrons with ions. As necessary condition for generation ESW, ion thermal velocity must be large enough so prevent decay acoustic waves. Another density larger than 30%...
The main scientific objectives of GEOTAIL Plasma Wave Instrument (PWI) are to investigate the characteristic features wave phenomena which generated by a variety plasma processes occurring within Earth's magnetosphere. PWI measures waves in frequency range from 5.62 Hz 800 kHz for electric components and 12.5 magnetic components. instrument is composed three distinct sets receivers: (1) Sweep Frequency Analyzer (SFA), (2) Multi-Channel (MCA) (3) Wave-Form Capture (WFC). first two receivers...
We develop a nonlinear wave growth theory of electromagnetic ion cyclotron (EMIC) triggered emissions observed in the inner magnetosphere. first derive basic equations from Maxwell's and momentum for electrons ions. then obtain that describe dynamics resonant protons interacting with an EMIC wave. The frequency sweep rate plays important role forming current controls growth. Assuming optimum condition maximum as absolute instability at magnetic equator self‐sustaining propagating equator, we...
Close examination of whistler mode chorus emissions reveals that a emission is coherent monochromatic wave typically with fast rising tone. The frequency the increases rapidly along growth amplitude. We first consider generation mechanism emissions. essential change critically related to inhomogeneity geomagnetic field in equatorial region. tone only possible when propagates away from equator interacting sufficient flux counterstreaming resonant electrons. Depletion trapped electrons phase...
Basic processes of coherent whistler mode wave‐particle interactions in the magnetosphere are studied by self‐consistent computer simulations. The wave equations used simulation to determine amplitude and frequency discussed physical interpretations them given. Nonlinear growth a uniform magnetic field examined detail. Difference between (periodic) nonuniform (encounter) is studied. Taking into account inhomogeneity dipole geomagnetic filed, we found that untrapped resonant electrons as well...
We present a new particle acceleration mechanism called ultra‐relativistic (URA). URA comprises electron energization due to special form of nonlinear phase trapping by coherent whistler‐mode wave for electrons with an initial Lorentz factor γ 0 satisfying > Ω EQ / ω ; is the frequency and cyclotron at equator assumed dipole magnetic field. Radiation belt that encounter combination relativistic turning (RTA) followed multiple interactions can undergo significant energy increase. Under...
We perform an electromagnetic full particle simulation to study the generation mechanism of VLF whistler‐mode chorus emissions in equatorial region magnetosphere. Parabolic variation static magnetic field is assumed as a model for dipole vicinity equator. have cold thermal electrons and relatively low anisotropic hot plasma particles. In initial phase, amplitude growth incoherent waves determined by linear rate. When wave reaches certain level, it begins grow more rapidly with series rising...