MHD WAVES IN THE COLLISIONAL PLASMA OF THE SOLAR CORONA AND TERRESTRIAL IONOSPHERE

We have studied MHD waves (Alfvén and fast compressional modes) in a homogeneous collisional three-component low-β plasma. The three-component plasma consists of electrons, ions, and neutrals with arbitrary ratio between collision frequencies and wave time scales. We have derived a general dispersion equation and relationships for phase velocity and collisional damping rates for MHD modes for various limiting cases: from weak collisions to a strong collisional coupling, and for longitudinal and oblique propagation. In a weak collision limit, the MHD eigen-modes are reduced to ordinary low-damping Alfvén and fast magnetosonic waves. For a partially ionized plasma with a strong collisional coupling of neutrals and ions, velocities of magnetosonic and Alfvén waves are substantially reduced, as compared to the Alfvén velocity in the ideal MHD theory. At a very low frequency, when neutrals and ions are strongly coupled, a possibility arises of weakly damping MHD modes, called “decelerated” MHD modes. These modes can be observed in the solar corona/chromosphere and in the F layer of the terrestrial ionosphere.

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MHD WAVES IN THE COLLISIONAL PLASMA OF THE SOLAR CORONA AND TERRESTRIAL IONOSPHERE

Solnechno-Zemnaya Fizika ◽

10.12737/szf-64202003 ◽

2020 ◽

Vol 6 (4) ◽

pp. 18-25

Author(s):

Anatoliy Nekrasov ◽

Vyacheslav Pilipenko

Keyword(s):

Solar Corona ◽

Low Frequency ◽

Mhd Waves ◽

Strongly Coupled ◽

Very Low Frequency ◽

Oblique Propagation ◽

Collisional Damping ◽

Component Plasma ◽

General Dispersion ◽

The Ideal

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Plasma Waves in the Inner Magnetosphere

10.1007/978-3-030-82167-8_4 ◽

2021 ◽

pp. 85-119

Author(s):

Hannu E. J. Koskinen ◽

Emilia K. J. Kilpua

Keyword(s):

Radiation Belt ◽

Low Frequency ◽

Plasma Waves ◽

Mhd Waves ◽

Particle Interactions ◽

Inner Magnetosphere ◽

Very Low Frequency ◽

Link Type ◽

Wave Modes

AbstractUnderstanding the role of plasma waves, extending from magnetohydrodynamic (MHD) waves at ultra-low-frequency (ULF) oscillations in the millihertz range to very-low-frequency (VLF) whistler-mode emissions at frequencies of a few kHz, is necessary in studies of sources and losses of radiation belt particles. In order to make this theoretically heavy part of the book accessible to a reader, who is not familiar with wave–particle interactions, we have divided the treatise into three chapters. In the present chapter we introduce the most important wave modes that are critical to the dynamics of radiation belts. The drivers of these waves are discussed in Chap. 10.1007/978-3-030-82167-8_5 and the roles of the wave modes as sources and losses of radiation belt particles are dealt with in Chap. 10.1007/978-3-030-82167-8_6.

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The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

Journal of Psychophysiology ◽

10.1027/0269-8803.23.4.191 ◽

2009 ◽

Vol 23 (4) ◽

pp. 191-198 ◽

Cited By ~ 26

Author(s):

Suzannah K. Helps ◽

Samantha J. Broyd ◽

Christopher J. James ◽

Anke Karl ◽

Edmund J. S. Sonuga-Barke

Keyword(s):

Brain Activity ◽

Sampling Rate ◽

Low Frequency ◽

Future Research ◽

Adhd Symptoms ◽

Default Mode ◽

Very Low Frequency ◽

Wide Range ◽

Interference Hypothesis ◽

Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

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