ULF waves and their influence on radiation belt dynamics in Earth's magnetosphere

Mapping Intimacies ◽

10.5194/egusphere-egu2020-13703 ◽

2020 ◽

Author(s):

Robert Rankin ◽

Alexander Degeling

Keyword(s):

Radiation Belt ◽

Geomagnetic Storms ◽

Low Frequency ◽

Recovery Phase ◽

Ulf Waves ◽

Wave Source ◽

Initial Plasma ◽

Plasma State ◽

Van Allen Probes ◽

Geomagnetic Fields

Recent observations from the Van Allen Probes mission have established that Pc3-5 ultra-low-frequency (ULF) waves can energize ions and electrons via drift-resonance and drift-bounce resonance. The extent to which these waves contribute to the space weather of the belts is relatively poorly understood and requires sophisticated modelling and characterization of the dominant wave modes that arise in the development and recovery phase of geomagnetic storms. Despite more than four decades of observations and theoretical analysis of ULF waves, there is no framework for accurately assessing the global distribution of ULF waves and their influence on the ring current.&#160; In this presentation, we describe a new global model of ULF waves that incorporates non-dipolar geomagnetic fields. The model is constrained using the GCPM of cold plasma density model and a specification of the ionosphere using the IRI and MSIS models. An algorithm is applied to adjust the initial plasma state to a quasi-static equilibrium that is then driven by a global convection electric field and ULF wave source. For specific observations by the Van Allen Probes and ARASE mission, the effect of these ULF waves on radiation belt ions and electrons is evaluated utilizing test-particle methodology and Liouville's theorem, which enables the phase space density to be followed and compared one-for-one with the satellite observations. &#160;

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Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

Annales Geophysicae ◽

10.5194/angeo-33-1431-2015 ◽

2015 ◽

Vol 33 (11) ◽

pp. 1431-1442 ◽

Cited By ~ 9

Author(s):

M. Georgiou ◽

I. A. Daglis ◽

E. Zesta ◽

G. Balasis ◽

I. R. Mann ◽

...

Keyword(s):

Radiation Belt ◽

Low Frequency ◽

Recovery Phase ◽

Wave Activity ◽

Magnetic Storms ◽

Ulf Waves ◽

Relativistic Electrons ◽

Outer Radiation Belt ◽

Magnetometer Arrays ◽

The One

Abstract. Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurrent observations of ultra-low-frequency (ULF) waves from the trans-Scandinavian IMAGE magnetometer network and stations from multiple magnetometer arrays available through the worldwide SuperMAG collaboration. The latitudinal and global distribution of Pc5 wave power is examined to determine how deep into the magnetosphere these waves penetrate. We then investigate the role of Pc5 wave activity deep in the magnetosphere in enhancements of radiation belt electrons population observed in the recovery phase of the magnetic storms. We show that, during magnetic storms characterized by increased post-storm electron fluxes as compared to their pre-storm values, the earthward shift of peak and inner boundary of the outer electron radiation belt follows the Pc5 wave activity, reaching L shells as low as 3–4. In contrast, the one magnetic storm characterized by irreversible loss of electrons was related to limited Pc5 wave activity that was not intensified at low L shells. These observations demonstrate that enhanced Pc5 ULF wave activity penetrating deep into the magnetosphere during the main and recovery phase of magnetic storms can, for the cases examined, distinguish storms that resulted in increases in relativistic electron fluxes in the outer radiation belts from those that did not.

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Comparison of External ULF wave Sources in Driving Radiation Belt Electron Dynamics

10.5194/egusphere-egu21-14176 ◽

2021 ◽

Author(s):

Zhe Niu ◽

Alexander Degeling ◽

Quanqi Shi

Keyword(s):

Radiation Belt ◽

Geomagnetic Storms ◽

Dynamic Pressure ◽

Wave Model ◽

Energetic Particles ◽

Generation Mechanism ◽

Mhd Waves ◽

Ulf Waves ◽

Wave Source ◽

Ulf Wave

For the study of Earth's radiation belts, an outstanding problem is the identification and prediction of dynamic variations of Earth's trapped energetic particles, in particular during geomagnetic storms. Statistical studies indicate that different types of geomagnetic storms (e.g. CIR and CME driven storms) have differing efficiencies in their ability to cause energization, transport and loss of energetic particles. This is most likely due to differences in the dominant mechanisms by which particles are affected between the storm types, and the locations within the magnetosphere where these mechanisms operate. For example, the dominant external generation mechanism for Pc5 ULF waves during CME driven storms may be magnetopause buffeting across the dayside, while for CIR driven storms the Kelvin-Helmholtz Instability (KHI) along the morning and evening flanks is more likely dominant. This changes the location and efficiency by which ULF waves can resonantly interact with radiation belt particles in these two storm types.In this study, we use a 2D MHD wave model to investigate how the dominant generation mechanism in the case of CIR and CME driven storms determines the ability for externally generated wave power to penetrate deeply into the magnetosphere. In order to do this, we model ideal MHD waves in a 2D box model magnetosphere with a parabolic magnetopause boundary layer. We consider how fluctuations in dynamic pressure generate magnetopause buffeting perturbations that launch MHD fast mode waves, following the approach of Degeling et al., JGR 2011. We also include in our simulation a simple model for magnetosheath flow, and calculate the local linear KHI growth rate for perturbations along the magnetopause flanks as a function of frequency to provide a KHI driven wave source.

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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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Variability of the pitch angle distribution of radiation belt ultrarelativistic electrons during and following intense geomagnetic storms: Van Allen Probes observations

Journal of Geophysical Research Space Physics ◽

10.1002/2015ja021065 ◽

2015 ◽

Vol 120 (6) ◽

pp. 4863-4876 ◽

Cited By ~ 24

Author(s):

Binbin Ni ◽

Zhengyang Zou ◽

Xudong Gu ◽

Chen Zhou ◽

Richard M. Thorne ◽

...

Keyword(s):

Pitch Angle ◽

Radiation Belt ◽

Geomagnetic Storms ◽

Angle Distribution ◽

Pitch Angle Distribution ◽

Van Allen Probes

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Variation of Radiation Belt Electron Flux During CME‐ and CIR‐Driven Geomagnetic Storms: Van Allen Probes Observations

Journal of Geophysical Research Space Physics ◽

10.1029/2019ja026771 ◽

2019 ◽

Vol 124 (8) ◽

pp. 6524-6540 ◽

Cited By ~ 3

Author(s):

Megha Pandya ◽

Veenadhari Bhaskara ◽

Yusuke Ebihara ◽

Shrikanth G. Kanekal ◽

Daniel N. Baker

Keyword(s):

Radiation Belt ◽

Electron Flux ◽

Geomagnetic Storms ◽

Van Allen Probes

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The dynamics of the inner boundary of the outer radiation belt during geomagnetic storms

10.5194/egusphere-egu2020-19607 ◽

2020 ◽

Author(s):

Xiaofei Shi ◽

Jie Ren ◽

Qiugang Zong

Keyword(s):

Radiation Belt ◽

Electron Flux ◽

Geomagnetic Storms ◽

Minimum Energy ◽

Onset Time ◽

Recovery Phase ◽

Outer Radiation Belt ◽

H Index ◽

Late Recovery ◽

Energy Dependent

We present a statistical study of energy-dependent and L shell-dependent inner boundary of the outer radiation belt during 37 isolated geomagnetic storms using observations from Van Allen Probes from 2013 to 2017. There are mutual transformations between "V-shaped" and "S-shaped" inner boundaries during different storm phases, resulting from the competition among electron loss, radial transport and local acceleration. The radial position, onset time, Est (the minimum energy at Lst where the inner boundary starts to exhibit an S-shaped form), and the radial width of S-shaped boundary (&#916;L) are quantitatively defined according to the formation of a reversed energy spectrum (electron flux going up with increasing energies from hundreds of keV to ~1 MeV) from a kappa-like spectrum (electron flux steeply falling with increasing energies). The case and statistical results present that (1) The inner boundary has repeatable features associated with storms: the inner boundary is transformed from S-shaped to V-shaped form in several hours during the storm commencement and main phase, and retains in the V-shaped form for several days until it evolves into S-shaped during late recovery phase; (2) &#916;L shows positive correlation with SYM-H index; (3) The duration of the V-shaped form is positively correlated with the storm intensity and the duration of the recovery phase; (4) The minimum energy Est are mainly distributed in the range of 100-550 keV. All these findings have important implications for understanding the dynamics of energetic electrons in the slot region and the outer radiation belt during geomagnetic storms.

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Reflection of low-frequency fast magnetosonic waves at the local two-ion cutoff frequency: observation in the plasmasphere

Annales Geophysicae ◽

10.5194/angeo-39-613-2021 ◽

2021 ◽

Vol 39 (4) ◽

pp. 613-625

Author(s):

Geng Wang ◽

Mingyu Wu ◽

Guoqiang Wang ◽

Sudong Xiao ◽

Irina Zhelavskaya ◽

...

Keyword(s):

Radiation Belt ◽

Cutoff Frequency ◽

Low Frequency ◽

Particle Dynamics ◽

Time Frequency ◽

Van Allen Probes ◽

Distinct Boundary ◽

Incident Waves ◽

The Waves ◽

Frequency Observation

Abstract. We investigate the reflection of low-harmonic fast magnetosonic (MS) waves at the local two-ion cutoff frequency (fcutHe+). By comparing the wave signals of the two Van Allen Probes satellites, a distinct boundary where wave energies cannot penetrate inward are found in the time–frequency domain. The boundary is identified as the time series of local fcutHe+. For a certain frequency, there exists a spatial interface formed by fcutHe+, where the incident waves should be reflected. The waves with small incident angles are more likely to penetrate the thin layer where the group velocity reduces significantly and then slow down in a period of several to tens of seconds before the reflection process complete. The cutoff reflection scenario can explain the intense outward waves observed by probe A. These results of MS reflection at fcutHe+ may help to predict the global distribution of MS waves and promote the understanding of wave–particle dynamics in the radiation belt.

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