Roles of magnetospheric convection on nonlinear drift resonance between electrons and ULF waves

In the Earth's inner magnetosphere, charged particles can be accelerated and transported by ultralow frequency (ULF) waves via drift resonance. We investigate the effects of magnetospheric convection on the nonlinear drift resonance process, which provides an inhomogeneity factor S to externally drive the pendulum equation that describes the particle motion in the ULF wave&#160; field. The S factor, defined as the ratio of the driving amplitude to the square of the pendulum trapping frequency, is found to vary with magnetic local time and as a consequence, oscillates quasi-periodically at the particle drift frequency. To better understand the particle behavior governed by the driven pendulum equation, we carry out simulations to obtain the evolution of electron distribution functions in energy and L-shell phase space. We find that resonant electrons can remain trapped by the low-m ULF waves under strong convection electric&#160; field, whereas for high-m ULF waves, the electrons trajectories can be significantly modified. More interestingly, the electron drift frequency is close to the nonlinear trapping frequency for intermediate-m ULF waves, which corresponds to chaotic motion of resonant electrons. These&#160; findings shed new light on the nature of particle coherent and diffusive transport in the inner magnetosphere.

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Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Annales Geophysicae ◽

10.5194/angeo-34-815-2016 ◽

2016 ◽

Vol 34 (9) ◽

pp. 815-829

Author(s):

Xiang Xu ◽

Chen Zhou ◽

Run Shi ◽

Binbin Ni ◽

Zhengyu Zhao ◽

...

Keyword(s):

Electron Temperature ◽

High Frequency ◽

Ring Current ◽

Modulation Frequency ◽

Current Source ◽

Temperature Oscillation ◽

Ulf Waves ◽

Ultralow Frequency ◽

Ulf Wave ◽

F Region

Abstract. Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.

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Global structure and properties of ULF waves in the ion foreshock observed in a Hybrid-Vlasov simulation.

10.5194/egusphere-egu21-6971 ◽

2021 ◽

Author(s):

Kun Zhang ◽

Seth Dorfman ◽

Urs Ganse ◽

Lucile Turc ◽

Chen Shi

Keyword(s):

Space Physics ◽

Ulf Waves ◽

Ion Distribution ◽

Geophysical Research ◽

Energetic Ions ◽

Ultralow Frequency ◽

Ulf Wave ◽

Wave Normal ◽

The Waves ◽

Wave Properties

Energetic ions reflected and accelerated by the Earth&#8217;s bow shock travel back into the solar wind, forming the ion foreshock, and generate ultralow frequency (ULF) waves. Such ULF waves have been extensively studied over the past few decades using satellite measurements. However, the spatial variations of the wave properties cannot be well resolved by satellite observations due to the limited number of available spacecraft simultaneously inside the ion foreshock. Therefore, we conduct a global survey of the ULF wave properties in the ion foreshock through analysis of a Vlasiator (a hybrid-Vlasov code) simulation. Previous studies validated that this simulation well reproduced Earth&#8217;s foreshock and the ULF waves in it [e.g., Palmroth et al., 2015; Turc et al., 2018]. Here we focus on the wave properties, including frequency, ellipticity, polarization, wave normal angle and growth rate, of the well-known 30-sec wave and its multiple harmonics. We report that the ULF waves near the edge of the foreshock are very different from the waves in the center of the foreshock. We also show the related ion distribution and discuss the connection between the observed ion beams and ULF waves, aiming at understanding the cause of the observed differences in wave properties.&#160;This study is supported by NASA grant 80NSSC20K0801. Vlasiator is developed by the European Research Council Starting grant 200141-QuESpace, and Consolidator grant GA682068-PRESTISSIMO received by the Vlasiator PI. Vlasiator has also received funding from the Academy of Finland. See www.helsinki.fi/vlasiator&#160;Palmroth, M., et al. (2015), ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared, J. Geophys. Res. Space Physics, 120, 8782&#8211;8798, doi:10.1002/2015JA021526.Turc, L., Ganse, U., Pfau-Kempf, Y., Hoilijoki, S., Battarbee, M., Juusola, L., et al. (2018). Foreshock properties at typical and enhanced interplanetary magnetic field strengths: results from hybrid-Vlasov simulations. Journal of Geophysical Research: Space Physics, 123, 5476&#8211;5493. doi:10.1029/2018JA025466.

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Modulation of chorus intensity by ULF waves deep in the inner magnetosphere

Geophysical Research Letters ◽

10.1002/2016gl070280 ◽

2016 ◽

Vol 43 (18) ◽

pp. 9444-9452 ◽

Cited By ~ 15

Author(s):

Zhiyang Xia ◽

Lunjin Chen ◽

Lei Dai ◽

Seth G. Claudepierre ◽

Anthony A. Chan ◽

...

Keyword(s):

Ulf Waves ◽

Inner Magnetosphere

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ULF Wave Power During Geomagnetic Storms and Implications for Radial Diffusion Processes

10.5194/egusphere-egu21-11203 ◽

2021 ◽

Author(s):

Jasmine Sandhu ◽

Jonathan Rae ◽

John Wygant ◽

Aaron Breneman ◽

Sheng Tian ◽

...

Keyword(s):

Statistical Analysis ◽

Diffusion Coefficients ◽

Radiation Belt ◽

Geomagnetic Storms ◽

Radial Diffusion ◽

Ulf Waves ◽

Wave Power ◽

Outer Radiation Belt ◽

Large Variability ◽

Ulf Wave

Ultra Low Frequency (ULF) waves drive radial diffusion of radiation belt electrons, where this process contributes to and, at times, dominates energisation, loss, and large scale transport of the outer radiation belt. In this study we quantify the changes and variability in ULF wave power during geomagnetic storms, through a statistical analysis of Van Allen Probes data for the time period spanning 2012 &#8211; 2019. The results show that global wave power enhancements occur during the main phase, and continue into the recovery phase of storms. Local time asymmetries show sources of ULF wave power are both external solar wind driving as well as internal sources from coupling with ring current ions and substorms.The statistical analysis demonstrates that storm time ULF waves are able to access lower L values compared to pre-storm conditions, with enhancements observed within L = 4. We assess how magnetospheric compressions and cold plasma distributions shape how ULF wave power propagates through the magnetosphere. Results show that the Earthward displacement of the magnetopause is a key factor in the low L enhancements. Furthermore, the presence of plasmaspheric plumes during geomagnetic storms plays a crucial role in trapping ULF wave power, and contributes significantly to large storm time enhancements in ULF wave power.The results have clear implications for enhanced radial diffusion of the outer radiation belt during geomagnetic storms. Estimates of storm time radial diffusion coefficients are derived from the ULF wave power observations, and compared to existing empirical models of radial diffusion coefficients. We show that current Kp-parameterised models, such as the Ozeke et al. [2014] model, do not fully capture the large variability in storm time radial diffusion coefficients or the extent of enhancements in the magnetic field diffusion coefficients.

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On the effect of ULF waves on the outer radiation belt during geomagnetic storms

10.5194/egusphere-egu21-5977 ◽

2021 ◽

Author(s):

Christopher Lara ◽

Pablo S. Moya ◽

Victor Pinto ◽

Javier Silva ◽

Beatriz Zenteno

Keyword(s):

Relativistic Electron ◽

Radiation Belt ◽

Geomagnetic Storms ◽

Cumulative Effect ◽

Radiation Belts ◽

Ulf Waves ◽

Relativistic Electrons ◽

Relative Role ◽

Outer Radiation Belt ◽

Ulf Wave

The inner magnetosphere is a very important region to study, as with satellite-based communications increasing day after day, possible disruptions are especially relevant due to the possible consequences in our daily life. It is becoming very important to know how the radiation belts behave, especially during strong geomagnetic activity. The radiation belts response to geomagnetic storms and solar wind conditions is still not fully understood, as relativistic electron fluxes in the outer radiation belt can be depleted, enhanced or not affected following intense activity. Different studies show how these results vary in the face of different events. As one of the main mechanisms affecting the dynamics of the radiation belt are wave-particle interactions between relativistic electrons and ULF waves. In this work we perform a statistical study of the relationship between ULF wave power and relativistic electron fluxes in the outer radiation belt during several geomagnetic storms, by using magnetic field and particle fluxes data measured by the Van Allen Probes between 2012 and 2017. We evaluate the correlation between the changes in flux and the cumulative effect of ULF wave activity during the main and recovery phases of the storms for different position in the outer radiation belt and energy channels. Our results show that there is a good correlation between the presence of ULF waves and the changes in flux during the recovery phase of the storm and that correlations vary as a function of energy. Also, we can see in detail how the ULF power change for the electron flux at different L-shell We expect these results to be relevant for the understanding of the relative role of ULF waves in the enhancements and depletions of energetic electrons in the radiation belts for condition described.

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Control of ULF Wave Accessibility to the Inner Magnetosphere by the Convection of Plasma Density

Journal of Geophysical Research Space Physics ◽

10.1002/2017ja024874 ◽

2018 ◽

Vol 123 (2) ◽

pp. 1086-1099 ◽

Cited By ~ 18

Author(s):

A. W. Degeling ◽

I. J. Rae ◽

C. E. J. Watt ◽

Q. Q. Shi ◽

R. Rankin ◽

...

Keyword(s):

Plasma Density ◽

Inner Magnetosphere ◽

Ulf Wave

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Geomagnetic activity and local time dependence of the distribution of ultra low-frequency wave power in azimuthal wavenumbers, m

Annales Geophysicae ◽

10.5194/angeo-35-629-2017 ◽

2017 ◽

Vol 35 (3) ◽

pp. 629-638 ◽

Cited By ~ 5

Author(s):

Theodore E. Sarris ◽

Xinlin Li

Keyword(s):

Phase Difference ◽

Low Frequency ◽

Field Measurements ◽

Resonant Interaction ◽

Total Power ◽

Ulf Waves ◽

Quiet Time ◽

Frequency Wave ◽

Drift Frequency ◽

Diffusion Rates

Abstract. The azimuthal wavenumber m of ultra low-frequency (ULF) waves in the magnetosphere is a required parameter in the calculations of the diffusion rates of energetic electrons and protons in the magnetosphere, as electrons and protons of drift frequency ωd have been shown to radially diffuse due to resonant interaction with ULF waves of frequency ω = mωd. However, there are difficulties in estimating m, due to lack of multipoint measurements. In this paper we use magnetic field measurements at geosynchronous orbit to calculate the cross-spectrogram power and phase differences between time series from magnetometer pairs. Subsequently, assuming that ULF waves of a certain frequency and m would be observed with a certain phase difference between two azimuthally aligned magnetometers, the fraction of the total power in each phase difference range is calculated. As part of the analysis, both quiet-time and storm-time distributions of power per m number are calculated, and it is shown that during active times, a smaller fraction of total power is confined to lower m than during quiet times. It is also shown that in the dayside region, power is distributed mostly to the lowest azimuthal wavenumbers m = 1 and 2, whereas on the nightside it is more equally distributed to all m that can be resolved by the azimuthal separation between two spacecraft.

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Magnetospheric convection electric field dynamics andstormtime particle energization: case study of the magneticstorm of 4 May 1998

Annales Geophysicae ◽

10.5194/angeo-22-497-2004 ◽

2004 ◽

Vol 22 (2) ◽

pp. 497-510 ◽

Cited By ~ 29

Author(s):

G. V. Khazanov ◽

M. W. Liemohn ◽

T. S. Newman ◽

M.-C. Fok ◽

A. J. Ridley

Keyword(s):

Electric Field ◽

Electric Fields ◽

Transport Model ◽

Storm Event ◽

Inner Magnetosphere ◽

Narrow Channels ◽

Near Earth Space ◽

Magnetospheric Convection ◽

Convection Electric Field ◽

Seed Population

Abstract. It is shown that narrow channels of high electric field are an effective mechanism for injecting plasma into the inner magnetosphere. Analytical expressions for the electric field cannot produce these channels of intense plasma flow, and thus, result in less entry and adiabatic energization of the plasma sheet into near-Earth space. For the ions, omission of these channels leads to an underprediction of the strength of the stormtime ring current and therefore, an underestimation of the geoeffectiveness of the storm event. For the electrons, omission of these channels leads to the inability to create a seed population of 10-100 keV electrons deep in the inner magnetosphere. These electrons can eventually be accelerated into MeV radiation belt particles. To examine this, the 1-7 May 1998 magnetic storm is studied with a plasma transport model by using three different convection electric field models: Volland-Stern, Weimer, and AMIE. It is found that the AMIE model can produce particle fluxes that are several orders of magnitude higher in the L = 2 – 4 range of the inner magnetosphere, even for a similar total cross-tail potential difference. Key words. Space plasma physics (charged particle motion and acceleration) – Magnetospheric physics (electric fields, storms and substorms)

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On the coupling between unstable magnetospheric particle populations and resonant high m ULF wave signatures in the ionosphere

Annales Geophysicae ◽

10.5194/angeo-23-567-2005 ◽

2005 ◽

Vol 23 (2) ◽

pp. 567-577 ◽

Cited By ~ 24

Author(s):

L. J. Baddeley ◽

T. K. Yeoman ◽

D. M. Wright ◽

K. J. Trattner ◽

B. J. Kellet

Keyword(s):

Wave Energy ◽

Low Frequency ◽

Distribution Functions ◽

Wave Number ◽

Particle Interactions ◽

Ion Distribution ◽

M Wave ◽

Ulf Wave ◽

Energy Dissipated ◽

Giant Pulsations

Abstract. Many theories state that Ultra Low Frequency (ULF) waves with a high azimuthal wave number (m) have their energy source in wave-particle interactions, yet this assumption has been rarely tested numerically and thus many questions still remain as to the waves' exact generation mechanism. For the first time, this paper investigates the cause and effect relationship between the driving magnetospheric particle populations and the ULF wave signatures as observed in the conjugate ionosphere by quantitatively examining the energy exchange that occurs. Firstly, a Monte Carlo method is used to demonstrate statistically that the particle populations observed during conjugate ionospheric high m wave events have more free energy available than populations extracted at random. Secondly, this paper quantifies the energy transferred on a case study basis, for two classes of high m waves, by examining magnetospheric Ion Distribution Functions, (IDFs) and directly comparing these with the calculated wave energy dissipated into the conjugate ionosphere. Estimates of the wave energy at the source and the sink are in excellent agreement, with both being of the order of 1010J for a typical high m wave. Ten times more energy (1011J) is transferred from the magnetospheric particle population and dissipated in the ionosphere when considering a subset of high m waves known as giant pulsations (Pgs). Previous work has demonstrated that 1010J is frequently available from non - Maxwellian IDFs at L=6, whereas 1011J is not. The combination of these studies thus provides an explanation for both the rarity of Pgs and the ubiquity of other high m waves in this region.

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