How Do Ultra‐Low Frequency Waves Access the Inner Magnetosphere During Geomagnetic Storms?

Rae, I. J.; Murphy, K. R.; Watt, Clare E. J.; Sandhu, Jasmine; Γεωργίου, Μαρίνα; Degeling, A. W.; Forsyth, C.; Bentley, Sarah; Staples, Frances; Shi, Quanqi

doi:10.1029/2019gl082395

Cited by 24 publications

(41 citation statements)

References 59 publications

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“…Furthermore, wave power propagating from the dayside magnetopause can be effectively reflected at the plasmapause boundary (Lee et al., 2002). In contrast with quiet time conditions and in agreement with the observations presented here, previous studies show that during storm times enhanced wave power is observed at very low radial distances and within L values of ∼4 (Georgiou et al., 2018; Lee et al., 2007; Loto’aniu et al., 2006; Rae et al., 2019). As highlighted by these studies, the accessibility of wave power to low L values can be enabled by changes in the Alfvén continuum.…”

Section: Discussionsupporting

confidence: 92%

ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A Statistical Analysis of Van Allen Probes Observations

et al. 2021

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Earth's inner magnetosphere is host to a population of highly variable, highly dynamic, and highly energetic particles known as the Van Allen radiation belts (Li & Hudson, 2019;Van Allen et al., 1958, 1959. Of particular interest is the outer radiation belt population that typically occupies radial distances greater than 3-4 R E and is host to extremely energetic MeV electrons. During geomagnetic storms, this population undergoes dramatic enhancements as well as rapid flux dropouts (e.g., Baker et al., 2004;Murphy et al., 2018;Turner et al., 2012). The MeV electron component of the outer radiation belt can cause problematic satellite

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Section: Discussionsupporting

confidence: 92%

ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A Statistical Analysis of Van Allen Probes Observations

et al. 2021

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“…Rae et al. (2019) showed the evolution of ground‐based ULF wave power during geomagnetic storms. ULF wave power can exhibit spatial coherence across ranges of L but does not rise and fall everywhere simultaneously due to the complicated evolution of cold plasma density and magnetic field strength in the inner magnetosphere.…”

Section: Discussionmentioning

confidence: 99%

Accounting for Variability in ULF Wave Radial Diffusion Models

2020

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Many modern outer radiation belt models simulate the long‐time behavior of high‐energy electrons by solving a three‐dimensional Fokker‐Planck equation for the drift‐ and bounce‐averaged electron phase space density that includes radial, pitch‐angle, and energy diffusion. Radial diffusion is an important process, often characterized by a deterministic diffusion coefficient. One widely used parameterization is based on the median of statistical ultralow frequency (ULF) wave power for a particular geomagnetic index Kp. We perform idealized numerical ensemble experiments on radial diffusion, introducing temporal and spatial variability to the diffusion coefficient through stochastic parameterization, constrained by statistical properties of its underlying observations. Our results demonstrate the sensitivity of radial diffusion over a long time period to the full distribution of the radial diffusion coefficient, highlighting that information is lost when only using median ULF wave power. When temporal variability is included, ensembles exhibit greater diffusion with more rapidly varying diffusion coefficients, larger variance of the diffusion coefficients and for distributions with heavier tails. When we introduce spatial variability, the variance in the set of all ensemble solutions increases with larger spatial scales of variability. Our results demonstrate that the variability of diffusion affects the temporal evolution of phase space density in the outer radiation belt. We discuss the need to identify important temporal and length scales to constrain variability in diffusion models. We suggest that the application of stochastic parameterization techniques in the diffusion equation may allow the inclusion of natural variability and uncertainty in modeling of wave‐particle interactions in the inner magnetosphere.

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“…Many auroral activities are related to the ULF waves in the magnetosphere, such as the substorm expansion phase onset 11 , the auroral arcs 12 , and the fluctuations of auroral intensity 13,14 . The ULF waves generated by the magnetopause surface wave propagate radially inwards 15 and penetrate deep inside the inner magnetosphere during geomagnetic storms 16 , while it is unknown whether the reverse process can occur.…”

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Plasmapause surface wave oscillates the magnetosphere and diffuse aurora

Guo

Dunn

et al. 2020

Nat Commun

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Energy circulation in geospace lies at the heart of space weather research. In the inner magnetosphere, the steep plasmapause boundary separates the cold dense plasmasphere, which corotates with the planet, from the hot ring current/plasma sheet outside. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations, but direct evidence of the waves and their role in magnetospheric dynamics have not yet been detected. Here, we show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multisatellite and ground-based measurements. The wave oscillates the plasmapause in the afternoon-dusk sector, triggers sawtooth auroral displays, and drives outward-propagating ultra-low frequency waves. We also show that the surface-wave-driven sawtooth auroras occurred in more than 90% of geomagnetic storms during 2014-2018, indicating that they are a systematic and crucial process in driving space energy dissipation.

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How Do Ultra‐Low Frequency Waves Access the Inner Magnetosphere During Geomagnetic Storms?

Cited by 24 publications

References 59 publications

ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A Statistical Analysis of Van Allen Probes Observations

ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A Statistical Analysis of Van Allen Probes Observations

Accounting for Variability in ULF Wave Radial Diffusion Models

Plasmapause surface wave oscillates the magnetosphere and diffuse aurora

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