北京大学地球与空间科学学院濮祖荫教授被美国地球物理学会任命为Journal of Geophysical Research（Space Physics）的新一届亚洲与太平洋区域主编，任期为4年（2006-2009）．

北京大学濮祖荫教授被推选为国际著名期刊Journal of Geophysical Research——Space Physics的主编

Whistlers and Related Ionospheric Phenomena

http://ieeexplore.ieee.org/iel7/7569814/7569815/07569878.pdf

Electromagnetic Shielding

©2015. American Geophysical Union. All Rights Reserved. Strong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August-September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13-22 September, initiated by a short-lived geomagnetic storm and characterized by a long period of primarily northward interplanetary magnetic field (IMF), showed strong depletion of relativistic electrons (including an unprecedented observation of long-lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth and the seed population (hundreds of keV) that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. If any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize. Key Points Source/seed energy electrons required to produce MeV radiation belt energization Substorm injections lead to VLF wave growth, producing MeV acceleration ULF waves may enhance loss/acceleration due to increased outward/inward diffusion

Source and seed populations for relativistic electrons: their roles in radiation belt changes

Dyadic Green Functions in Electromagnetic Theory by Chen-To-Tai.Book review.

Controlled experiments involving injection of 0.5 Hz – 8 kHz electromagnetic waves into the Earth’s magnetosphere have played an important role in discovering and elucidating wave-particle interactions in near-Earth space. Due to the significant engineering challenges of efficiently radiating in the ELF/VLF: 300 Hz – 30 kHz band, few experiments have been able to provide sustained transmissions of sufficient power to excite observable effects for scientific studies. Two noteworthy facilities that were successful in generating a large database of pioneering and repeatable observations were the Siple Station Transmitter in Antarctica and the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. Both facilities were able to excite Doppler shifted cyclotron resonance interactions leading to linear and nonlinear wave amplification, triggering of free running emissions, and pitch angle scattering of energetic electrons. Amplified and triggered waves were primarily observed on the ground in the geomagnetic conjugate region after traversal of the magnetosphere along geomagnetic field aligned propagation paths or in the vicinity of the transmitter following two traversals of the magnetosphere. In several cases, spacecraft observations of the amplified and triggered signals were also made. The observations show the amplifying wave particle interaction to be dynamically sensitive to specific frequency and also specific frequency-time format of the transmitted wave. Transmission of multiple coherent waves closely spaced in frequency showed that the wave particle interaction requires a minimum level of coherency to enter the nonlinear regime. Theory and numerical simulations point to cyclotron resonance with counter streaming particles in the 10-100 keV range as the dominant process. A key feature of the nonlinear interaction is the phase-trapping of resonant particles by the wave that is believed to drive non-linear wave amplification and the triggering of free-running emissions. Observations and modeling of controlled wave injections have important implications for naturally occurring whistler mode emissions of hiss and chorus and the broader phenomena of radiation belt dynamics. A review of observational, theoretical, and numerical results is presented and suggestions for future studies are made.

/pdf/review-of-controlled-excitation-of-non-linear-wave-particle-2c54g0emlr.pdf

Review of Controlled Excitation of Non-linear Wave-Particle Interactions in the Magnetosphere

Evidence of Small Scale Plasma Irregularity Effects on Whistler Mode Chorus Propagation

Observations of magnetospheric VLF (∼3-30 kHz) chorus being triggered by lightning induced whistlers are rare but provide a unique opportunity to remotely diagnose wave-particle interactions in the Earth's radiation belts. The observations presented here are unique in that whistlers originating from lightning in the southern hemisphere are seen to trigger upper band chorus repeatedly over the course of two hours, yielding 12 observation cases with very similar characteristics. Each whistler exhibits a distinct upper frequency cutoff and only the lowest L-shell whistler is observed to trigger upper band chorus. The observed cutoff frequencies along with L-shell and cold plasma density derived from dispersion analysis are used to estimate the anisotropy of the hot plasma distribution in the magnetosphere. Resulting anisotropy estimates are in good agreement with previous in-situ measurements and past work. While the anisotropy of the hot plasma distribution determines wave growth in the linear regime, access to the nonlinear regime requires the in situ wave amplitude to exceed the threshold for phase trapping of energetic electrons. Calculation of the threshold for each whistler shows that the upper band triggering of chorus corresponds to a lower nonlinear threshold. The results suggest that while upper band chorus is less favorable to be spontaneously generated, the conditions in this band are more conducive for triggering of the chorus instability by an external input wave.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL081391

Remote Sensing of Radiation Belt Energetic Electrons Using Lightning Triggered Upper Band Chorus

Modeling of gyroresonant wave-particle interactions in the radiation belts requires solving the Vlasov-Maxwell system of equations in an inhomogenous background geomagnetic field. Previous works have employed particle-in-cell methods or Eulerian solvers (such as the Vlasov Hybrid Simulation code) to provide numerical solutions to the problem. In this report, we provide an alternative numerical approach by utilizing a first order finite difference upwind scheme. When coupled to the narrowband Maxwell's equations, the model reproduces linear as well as nonlinear wave growth of coherent signals. Wave growth is nonlinear growth when the wave amplitude exceeds the minimum value for phase trapping of counterstreaming particles and is linear otherwise. The model also demonstrates free-running frequency variation for a case with a high linear growth rate. In addition, the model confirms the theoretical prediction of a stable “phase-space hole” during the nonlinear growth process. The plasma parameters and L shell used in this study are typical of those associated with the Siple Station wave injection experiment.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014GL061787

Finite difference modeling of coherent wave amplification in the Earth's radiation belts

The interaction between coherent whistler mode waves and energetic radiation belt electrons can result in pitch angle scattering of electrons into the bounce loss cone and subsequent precipitation. In studying the effects of VLF transmitter signals on particle precipitation, past modeling efforts have focused on the computation of diffusion coefficients for a Fokker-Planck model. In contrast, to capture the nonlinear effects of large-amplitude coherent waves, we evaluate particle precipitation using a Vlasov-Liouville (VL) model which computes the phase space particle distribution function directly using a characteristic-based solution of the Vlasov equation. Previous work has shown that in the case of large-amplitude coherent waves, phase trapping can significantly perturb resonant particles from their adiabatic paths. We evaluate the importance of phase trapping over a range of wave amplitudes (up to 200 pT); the percentage of particles that precipitate after being phase trapped is computed over a phase space grid in the loss cone. The results demonstrate that phase trapping contributes significantly to precipitation when a large-amplitude wave (>100 pT) is present. Additionally, linear theory can be valid over a broad range of amplitudes and the relative accuracy of linear theory in calculating the precipitated flux depends strongly on the initial particle distribution. Additionally, we demonstrate the ability of the VL model to calculate the time evolution of the precipitated flux due to short-duration whistler mode pulses. The physical parameters used in this study are typical of those associated with the Siple Station wave injection experiment.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JA019809

Vijay Harid

Papers

Review of Controlled Excitation of Non-linear Wave-Particle Interactions in the Magnetosphere

Evidence of Small Scale Plasma Irregularity Effects on Whistler Mode Chorus Propagation

Remote Sensing of Radiation Belt Energetic Electrons Using Lightning Triggered Upper Band Chorus

Finite difference modeling of coherent wave amplification in the Earth's radiation belts

Theoretical and numerical analysis of radiation belt electron precipitation by coherent whistler mode waves