Vijay Harid

University of Colorado Denver

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Mark Gołkowski

University of Colorado Denver

U. S. Inan

Stanford University

M. Spasojević

Stanford University

Poorya Hosseini

University of Colorado Denver

M. B. Cohen

Georgia Institute of Technology

O. V. Agapitov

University of California, Berkeley

J. D. Li

Stanford University

Morris A. Cohen

University of Pennsylvania

D. L. Carpenter

Stanford University

T. F. Bell

Stanford University

Cooperative Institutions

Stanford University

University of Colorado Denver

SLAC National Accelerator Laboratory

United States Naval Research Laboratory

Naval Research Laboratory Plasma Physics Division

Georgia Institute of Technology

University of California, Berkeley

Space Science Institute

University of Colorado Anschutz Medical Campus

University of Iowa

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Siple Station, Antarctica, Statistics of Magnetospheric ELF/VLF Wave Growth

AGU Fall Meeting Abstracts (2011)

J. Li Morris A. Cohen Vijay Harid M. Spasojević J. Papon

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Citations (0)

Empirical Parameterization of Broadband VLF Attenuation in the Earth‐Ionosphere Waveguide

Journal of Geophysical Research Space Physics (2023)

R. Said Mark Gołkowski Vijay Harid

Abstract The Earth‐ionosphere waveguide (EIW) determines the propagation of Very Low Frequency (VLF; ∼3−30 kHz) waves. Characterizing the waveguide is a longstanding challenge due to its large spatial scale and the complex variability of the lower ionosphere. Here we apply a novel linear basis function regression technique to characterize attenuation in the EIW using broadband measurements of lightning‐generated radio waves. The process begins with defining a basis function set, which ideally encompasses a feature set that can predict the variability seen in VLF attenuation properties. With this basis set defined, a system of linear equations is then constructed using sensor pair observations to eliminate the dependency on source amplitude in each observation. Using this formalism, an empirical attenuation model for broadband signals from lightning is constructed and the dependence on attenuation properties with the boundary conditions is explored. The empirically derived results show attenuation rates over ice that are 12 dB/Mm higher compared to paths over saltwater. Well‐known east/west attenuation rate asymmetry stemming from anisotropic reflection coefficients of the ionosphere is also demonstrated and investigated. For example, under a daytime ionosphere, westward‐propagating waves suffer up to 2.8 dB/Mm greater attenuation compared to eastward‐propagating waves. The trained model is used for propagation corrections in a global lightning locating system (LLS), but this technique can be expanded to further study VLF attenuation rates by employing different sets of basis functions.

Earth–ionosphere waveguide

Waveguide

10.1029/2022ja030742

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Citations (3)

Empirical Parameterization of Broadband VLF Attenuation in the Earth-Ionosphere Waveguide

Zenodo (CERN European Organization for Nuclear Research) (2023)

R. Said Mark Gołkowski Vijay Harid

Earth–ionosphere waveguide

Waveguide

10.5281/zenodo.7671994

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Citations (0)

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

Journal of Geophysical Research Space Physics (2014)

Vijay Harid Mark Gołkowski T. F. Bell U. S. Inan

Abstract 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.

Electron precipitation

Whistler

Pitch angle

10.1002/2014ja019809

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Citations (18)

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

Geophysical Research Letters (2021)

Poorya Hosseini O. V. Agapitov Vijay Harid Mark Gołkowski

Abstract The impact of randomly distributed field‐aligned density irregularities on whistler‐mode wave propagation is investigated using full‐wave simulations and multipoint spacecraft observations. The irregularities are modeled as randomized density perturbations between 1% and 10% of the nominal background density value with scales of ∼10–60 km transverse and ∼50–500 km along the background magnetic field. The density irregularities affect whistler wave propagation and lead to spatial modulation of wave average power density accompanied by spreading of the wave normal angle distribution. Wave power variation is shown to statistically increase with the depth of density irregularities. The simulation results are in good agreement with the observed correlations of chorus power and variation of the plasma density from multipoint observations by the four Magnetosphere MultiScale spacecraft. The change in fundamental wave properties from scattering from these irregularities affects the efficiency of wave‐particle interactions in the radiation belts and needs to be incorporated into large‐scale energetic‐particle flux models.

Whistler

Wave Power

Pitch angle

10.1029/2021gl092850

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Citations (33)

Laboratory Investigation of Nonlinear Sub-cyclotron Damping

2022 International Conference on Electromagnetics in Advanced Applications (ICEAA) (2023)

Erik Tejero Jim Schroeder Fred Skiff Ami DuBois C. L. Enloe

A unique feature of whistler chorus wave observations is the power gap at frequencies near half the electron gyrofrequency, which is observed approximately 2/3 of the time. Additionally, some of these observations have multiple power gaps, which are typically oblique chorus waves. A variety of theories have been developed over the decades to explain these power gaps, including excitation by two separate electron populations, damping due to nonlinear wave-particle interactions, and lower band cascade generating the upper band through coupling between electrostatic and electromagnetic components of lower band waves. Recently, Gao et al. (J. Geophys. Res., 123, 7462, 2018) published a statistical survey of the whistler chorus power gap using seven years of chorus observations from THEMIS. The results of the survey are that the theories involving damping due to nonlinear wave-particle interactions are the most consistent with the observations, but that they do not each explain all the observations. This led the authors to conclude that the power gaps may be a result of a combination of mechanisms or may require new mechanisms. We are currently conducting laboratory experiments coupled with numerical simulations to test the theories most consistent with observations: nonlinear Landau damping and nonlinear subcyclotron damping.

Whistler

Landau damping

Chorus

10.1109/iceaa57318.2023.10297703

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

Geophysical Research Letters (2019)

Poorya Hosseini Mark Gołkowski Vijay Harid

Abstract Observations of magnetospheric 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 herein are unique in that whistlers, originating from lightning, are seen to trigger upper band chorus repeatedly over the course of 2 hr. Each whistler exhibits a distinct upper frequency cutoff that is used to estimate the anisotropy of the hot plasma distribution. Resulting anisotropy estimates are in good agreement with previous in situ measurements. While the anisotropy 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. 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.

Whistler

Chorus

Lightning

Van Allen Probes

Cutoff frequency

10.1029/2018gl081391

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Citations (17)

Automated Large‐Scale Extraction of Whistlers Using Mask‐Scoring Regional Convolutional Neural Network

Geophysical Research Letters (2021)

Vijay Harid Chao Liu Yan Pang Akimun Jannat Alvina Mark Gołkowski

Abstract Extremely and very low frequency (ELF/VLF) radio waves are generated from a variety of natural geophysical sources. Ground‐based observations often contain signals of interest; however, the signals are typically immersed in a noisy environment due to lightning‐generated sferics and additional anthropogenic sources. Although automated detection algorithms have been employed successfully in the past, extraction of arbitrary and broadband signal classes has been a challenge. In this work, we employ a mask‐scoring regional convolutional neural network (MSRCNN) for automated extraction of whistlers from ground measurements at Palmer station, Antarctica. Statistics of several hundred thousand whistler receptions are evaluated to determine seasonal and diurnal variations at Palmer station along with strong correlations to lightning activity in the conjugate hemisphere. Although MSRCNN has been employed for whistler extraction in this work, the method has can be easily extended to other signal classes including chorus, hiss, and VLF triggered emissions.

Whistler

Hiss

Lightning

Atmospherics

10.1029/2021gl093819

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Citations (8)

Preferential Magnetospheric Power Excitation by Rising Frequency Ramps from 1986 Siple Station Data

AGUFM (2013)

J. Li M. Spasojević Vijay Harid Mark Gołkowski D. L. Carpenter

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Preferential amplification of rising versus falling frequency whistler mode signals

Geophysical Research Letters (2014)

J. D. Li Vijay Harid M. Spasojević Mark Gołkowski U. S. Inan

Abstract Analysis of ground‐based ELF/VLF observations of injected whistler mode waves from the 1986 Siple Station experiment demonstrates the preferential magnetospheric amplification of rising over descending frequency‐time ramps. From examining conjugate region receptions of ±1 kHz/s frequency‐time ramps, we find that rising ramps generate an average total power 1.9 times higher than that of falling frequency ramps when both are observed during a transmission. And in 17% of receptions, only rising ramps are observed above the noise floor. Furthermore, the amplification ratio inversely correlates with the noise and total signal power. Using a narrowband Vlasov‐Maxwell numerical simulation, we explore the preferential amplification due to differences in linear growth rate as a function of frequency, relative to the frequency which maximizes the linear growth rate for a given anisotropy, and in nonlinear phase trapping. These results contribute to the understanding of magnetospheric wave amplification and the preference for structured rising elements in chorus.

Whistler

Falling (accident)

Substorm

Narrowband

10.1002/2014gl062359

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Citations (5)