Automated identification of discrete, lightning-generated, multiple-dispersed whistler waves in C/NOFS-VEFI very low frequency observations

Discrete very-low-frequency chorus emissions observed during the daytime at ground station Gulmarg (geomag. lat. 24°10′N) are reported. The generation of these emissions is explained in terms of transverse resonance interaction between whistler waves and counter-streaming energetic electrons. The theory is tested by evaluating different parameters.

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Lightning‐Generated Whistler Amplitudes Measured by the Van Allen Probes

10.5194/egusphere-egu21-889 ◽

2021 ◽

Author(s):

Thomas Farges ◽

Jean-Francois Ripoll ◽

David Malaspina ◽

Erin Lay ◽

Gregory Cunningham ◽

...

Keyword(s):

World Wide ◽

Low Frequency ◽

Whistler Waves ◽

Mean Power ◽

Very Low Frequency ◽

Van Allen Probes ◽

Whistler Mode Waves ◽

The Mean ◽

Vlf Waves ◽

Field Wave

<p>This talk will show a statistical analysis of both electric and magnetic field wave amplitudes of very low frequency lightning&#8208;generated whistlers (LGWs) based on the equivalent of 11.5 years of observations made by the Van Allen Probes. We complement this analysis with data from the ground&#8208;based World Wide Lightning Location Network (WWLLN) to explore differences between satellite and ground&#8208;based measurements. We will discuss how LGW mean amplitudes were generally found to be low compared with other whistler mode waves even though there exists extreme events (1 out of 5,000) that can reach 100 pT and contribute strongly to the mean power below L = 2. We will reveal a region of low wave amplitude existing below L=2 thanks to the denser dayside ionosphere, which prevents the intense equatorial lightning VLF waves from propagating through it. Below L = 1.5 at all MLT, LGW amplitudes are found to be weak while the ground&#8208;level lightning activity is maximal. This suggests a difficulty of lightning VLF waves to penetrate / propagate / remain at low L&#8208;shells, certainly due at least to the denser ionosphere during daytime. On the contrary, the mean LGW magnetic power (or RMS) remains nearly constant with respect to L&#8208;shell. We will explain that this is due to strong to extreme LGWs that dominate the wave mean power to the point of compensating the decay of LGW occurrence at low L&#8208;shell. Even though extreme LGW were found to be very powerful, particularly at low L and during night, the mean electric/magnetic power remains low compared with other whistler waves. This implies that LGW resonant effects on electrons are consequently long&#8208;term effects that contribute to &#8220;age&#8221; trapped inner belt electron populations.</p>

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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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