ULF Waves at the Magnetopause

Plaschke, Ferdinand

doi:10.1002/9781119055006.ch12

Cited by 13 publications

(10 citation statements)

References 121 publications

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“…ULF waves were first reported in conjunction with a large geomagnetic storm and auroral activity observed between 28 August and 7 September 1859 (Stewart, 1861). Since then an extensive body of observational and theoretical work has been established regarding the generation, spectral, spatial, and temporal characteristics of these waves (see the reviews by Elkington, 2006; Menk, 2011; Plaschke, 2016; Rae & Watt, 2016; Takahashi, 2016; Volwerk, 2016). For example it has been demonstrated that ULF wave power is enhanced during elevated solar wind conditions (e.g., Anderson, 1994; Bentley et al, 2019; Murphy et al, 2011; Pahud et al, 2009; Rae et al, 2012; Takahashi & Ukhorskiy, 2007) and enhanced geomagnetic activity (e.g., Brautigam et al, 2005; Hartinger et al, 2015; Ozeke et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

et al. 2020

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Ultralow frequency (ULF) waves are electromagnetic pulsations observed throughout the magnetosphere driven by processes both external and internal to the magnetosphere. Within the magnetosphere, discrete and broadband ULF wave activity can couple to the local plasma via coherent or stochastic wave-particle interactions. These wave-particle interactions can lead to dynamic changes in local plasma including rapid acceleration and transport of radiation belt electrons. Using observations from GOES-15 and the Automated Flare Inference of Oscillations algorithm we investigate the distribution and occurrence of broadband and discrete ULF waves to help understand the relative importance of coherent and stochastic wave-particle interactions. We find that intervals of discrete ULF waves are more commonly identified during slow and low-density solar wind and when B z is near zero. Broadband waves are more commonly identified during periods of active solar wind, including periods of high solar wind speeds and large density perturbations, and large negative B z. We also find that under all solar wind conditions the number of intervals of broadband ULF wave power exceeds that of discrete wave power; for example, ULF wave activity is more likely to be broadband. These results suggest that radial diffusion due to incoherent broadband waves is an important driver of wave-particle interactions, especially during active solar wind conditions. However, the presence of discrete waves during both active and quiet solar wind conditions suggests that these waves and the corresponding wave-particle interactions cannot be ignored, especially since discrete wave-particle interactions tend to be more efficient than radial diffusion.

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Section: Introductionmentioning

confidence: 99%

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

et al. 2020

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“…In MHD simulations (e.g., Leonovich et al, 2016; Nakariakov et al, 2016), propagation of ULF perturbations can be well resolved, which essentially depends on scales and dynamics of the perturbation source (e.g., Klimushkin et al, 2019; Wright & Elsden, 2020). Magnetopause dynamics (Hartinger et al, 2013; Plaschke, 2016) or plasmasheet injections (Liu et al, 2017; Runov et al, 2014) can act as the source for ULF perturbations. Moreover, another ULF wave source is the injection of energetic ions that can generate ULF waves via resonant wave‐particle interaction (Glassmeier et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

“…In this study, the term ULF perturbation includes both (1) ULF waves/pulsations (i.e., signals observationally defined in Jacobs et al, 1964 to last at least a few wave cycles) and (2) transient perturbations with ULF time scales, such as impulses and step‐like changes that would not fit the observational definition of Jacobs et al (1964) yet may still be MHD modes. ULF perturbations can be directly driven by solar wind transients (see, e.g., Bentley et al, 2018; Hartinger et al, 2013; Shen et al, 2015; Wang et al, 2017 and references therein), sustained magnetopause oscillations (Agapitov et al, 2009; Hartinger et al, 2015; Hwang & Sibeck, 2016; Plaschke, 2016), or a combination of the two (Hartinger et al, 2014; Kepko & Viall, 2019). Given the many pathways by which ULF perturbations can drive energy transport from the solar wind (through the magnetopause) to the inner magnetosphere, there remain many unresolved questions concerning their coupling to inner magnetosphere dynamics.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Whistler Waves by Ultra‐Low‐Frequency Perturbations: The Importance of Magnetopause Location

et al. 2020

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Ultra-low-frequency (ULF, 0.001-1 Hz) perturbations are important aspect of the dynamics in the inner magnetosphere: They are responsible for radial transport (diffusion) of high-energy electrons and for energizing the ionosphere with field-aligned currents. This study is devoted to properties of ULF perturbations generated at the magnetopause, their propagation into the inner magnetosphere, and their modulation of whistler-mode very-low-frequency (VLF) waves. Taking advantage of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission configuration in 2019, we investigate ULF perturbations simultaneously captured by three spacecraft at different distances from the magnetopause. Combining ground-based and THEMIS measurements of ULF perturbations to separate temporal and spatial variations of their properties, we show that their intensity decays exponentially with distance from the magnetopause as close as the geostationary orbit. Near the magnetopause ULF perturbations can modulate whistler-mode (VLF) waves effectively: Close to the magnetopause, VLF wave bursts have the same periodicity as the ULF perturbations. Our results demonstrate that almost the entire outer magnetosphere (from the geostationary orbit to L ∼ 12), including the outer radiation belts, is significantly influenced by ULF perturbations excited by magnetopause dynamic responses to the solar wind.

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“…Strong plasma pressure and magnetic field gradients at the magnetopause serve as a free energy source for various plasma waves that enable stochastic charged particle diffusion across the magnetic surfaces (e.g., Chen et al, 2015;Galeev et al, 1986;Johnson & Cheng, 1997;Treumann, 1999, and references therein). The stochastic transport can be enhanced by large-scale magnetopause perturbations as Kelvin-Helmholtz vortexes (e.g., Chen et al, 2015;Fairfield et al, 2000;Hasegawa et al, 2004;Nakai & Ueno, 2011) or as various surface waves (e.g., De Keyser & Roth, 2003;Plaschke, 2016;Sibeck et al, 1990) usually observed at the flanks of the magnetosphere. Such plasma transport results in formation of a boundary layer with a monotonic, gradual plasma density profile (e.g., De Keyser et al, 2004;Fujimoto et al, 1997Fujimoto et al, , 1998Phan, 1997).…”

Section: Introductionmentioning

confidence: 99%

Properties of the Equatorial Magnetotail Flanks ∼50–200 R_E Downtail

et al. 2017

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In space, thin boundaries separating plasmas with different properties serve as a free energy source for various plasma instabilities and determine the global dynamics of large‐scale systems. In planetary magnetopauses and shock waves, classical examples of such boundaries, the magnetic field makes a significant contribution to the pressure balance and plasma dynamics. The configuration and properties of such boundaries have been well investigated and modeled. However, much less is known about boundaries that form between demagnetized plasmas where the magnetic field is not important for pressure balance. The most accessible example of such a plasma boundary is the equatorial boundary layer of the Earth's distant magnetotail. Rather, limited measurements since its first encounter in the late 1970s by the International Sun‐Earth Explorer‐3 spacecraft revealed the basic properties of this boundary, but its statistical properties and structure have not been studied to date. In this study, we use Geotail and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) missions to investigate the equatorial boundary layer from lunar orbit (∼55 Earth radii, RE, downtail) to as far downtail as ∼200 RE. Although the magnetic field has almost no effect on the structure of the boundary layer, the layer separates well the hot, rarefied plasma sheet from dense cold magnetosheath plasmas. We suggest that the most important role in plasma separation is played by polarization electric fields, which modify the efficiency of magnetosheath ion penetration into the plasma sheet. We also show that the total energies (bulk flow plus thermal) of plasma sheet ions and magnetosheath ions are very similar; that is, magnetosheath ion thermalization (e.g., via ion scattering by magnetic field fluctuations) is sufficient to produce hot plasma sheet ions without any additional acceleration.

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ULF Waves at the Magnetopause

Cited by 13 publications

References 121 publications

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

Modulation of Whistler Waves by Ultra‐Low‐Frequency Perturbations: The Importance of Magnetopause Location

Properties of the Equatorial Magnetotail Flanks ∼50–200 R_E Downtail

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ULF Waves at the Magnetopause

Cited by 13 publications

References 121 publications

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

Inner Magnetospheric ULF Waves: The Occurrence and Distribution of Broadband and Discrete Wave Activity

Modulation of Whistler Waves by Ultra‐Low‐Frequency Perturbations: The Importance of Magnetopause Location

Properties of the Equatorial Magnetotail Flanks ∼50–200 RE Downtail

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Properties of the Equatorial Magnetotail Flanks ∼50–200 R_E Downtail