Correlations between very low frequency chorus bursts and impulsive magnetic variations at L ~ 4.5

1981 ◽  
Vol 59 (8) ◽  
pp. 1034-1041 ◽  
Author(s):  
S. Kokubun ◽  
K. Hayashi ◽  
T. Oguti ◽  
K. Tsuruda ◽  
S. Machida ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Range ◽  
Conductivity Enhancement ◽  
Very Low Frequency ◽  
Close Relationship ◽  
Magnetic Pulsations ◽  
Whistler Mode Waves ◽  
Short Time ◽  
Vlf Emissions ◽  
Vlf Waves

Coordinated observations of aurora, ULF, and VLF waves were made at 13 stations in Canada in January and February, 1980. The analysis of simultaneous ULF and VLF data obtained at Park Site (L = 4.4) revealed a close relationship between irregular magnetic pulsations and VLF emissions in the frequency range of 1.5–5 kHz. One-to-one correlations were observed between VLF chorus bursts and impulsive magnetic variations, called magnetic impulses, during sub-storms of Kp ≥ 4+ on the local morning-to-noon side. VLF chorus bursts consist of discrete risers of 0.1–0.3 s duration. It is found that magnetic impulses with a rise time of 0.5–1 s and with a duration of ~2 s coincide with the occurrence of VLF riser groups of a similar duration within ~2 s. This short time difference strongly suggests that magnetic impulses are caused by a conductivity enhancement due to electron precipitation induced by whistler mode waves.

Lightning‐Generated Whistler Amplitudes Measured by the Van Allen Probes

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‐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‐based World Wide Lightning Location Network (WWLLN) to explore differences between satellite and ground‐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‐level lightning activity is maximal. This suggests a difficulty of lightning VLF waves to penetrate / propagate / remain at low L‐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‐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‐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‐term effects that contribute to “age” trapped inner belt electron populations.</p>

scholarly journals Investigation of the Sudden Solar Ionospheric Disturbance using Radio Telescope

2020 ◽  
Vol 240 ◽  
pp. 07003
Author(s):  
Adam Aqasha ◽  
Andrien Zheng ◽  
Sneha Athreya ◽  
Hoe Teck Tan
Keyword(s):  
Solar Flares ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
The Sun ◽  
Radio Telescopes ◽  
Very Low Frequency ◽  
Set Up ◽  
Vlf Waves

Low-frequency radio telescopes are cheap and useful devices for the investigation of terrestrial and extra-terrestrial emissions. These emissions come either from the Sun and the planet Jupiter to terrestrial emissions. This project aims to investigate the Very Low Frequency (VLF) waves from mid-August to October 2019 using Radio JOVE (20 MHz) and SSID (3-30 kHz) to observe for the occurrence of solar flares and see how if the radio telescopes that the team set up is reliable. This will allow us future students aspiring to learn about astronomy to examine solar flares in detail during the upcoming solar maximum. Not many flares were detected as this period happens to be a solar minimum. However, a series of flares occurred between 30 September 2019 and 1 October 2019, which the telescopes have been able to detect, particularly SSID.

Extremely low frequency detection of electrical discharges at Minamidake crater (Sakurajima volcano, Japan)

2020 ◽  
Author(s):  
Caron E.J. Vossen ◽  
Corrado Cimarelli ◽  
Alec J. Bennett ◽  
André Geisler ◽  
Damien Gaudin ◽  
...  
Keyword(s):  
Low Frequency ◽  
Japan Meteorological Agency ◽  
Frequency Range ◽  
Electrical Discharges ◽  
Very Low Frequency ◽  
Extremely Low Frequency ◽  
Sakurajima Volcano ◽  
Frequency Detection ◽  
The World ◽  
Active Volcanoes

<p>Volcanoes are increasingly better monitored around the world. Nonetheless, the detection and monitoring of volcanic ash plumes remains difficult, especially in remote areas. Intense electrical activity and lightning in volcanic plumes suggests that electrical monitoring of active volcanoes can aid the detection of ash emissions in near real-time. Current very low frequency and wide-band thunderstorm networks have proven to be able to detect plumes of large magnitude. However, the time delay and the relatively high number of non-detected explosive episodes show that the applicability of these systems to the detection of smaller (and often more frequent) ash-rich explosive events is limited. Here we use a different type of thunderstorm detector to observe electrical discharges generated by the persistent Vulcanian activity of Minamidake crater at Sakurajima volcano in Japan. The sensors consist of two antennas that measure the induced current due to the change in electric field with time. In contrast to the current thunderstorm networks, these sensors measure within the extremely low frequency range (1-45 Hz) and can detect lightning up to 35 kilometres distance.</p><p>Two detectors were installed at a distance of 3 and 4 kilometres from Minamidake crater and recorded almost continuously since July 2018. Within this period, the ash plumes reached a maximum height of 5.5 kilometres above the crater rim. Using a volcanic lightning detection algorithm and the catalogue of volcanic explosions compiled by the Japan Meteorological Agency (JMA), the number of electrical discharges was determined for each individual explosive event. In addition, the start of electrical discharges was compared to the eruption onset estimated by the JMA.</p><p>Preliminary results show that the detector closest to the crater had the highest detection efficiency. It detected electrical discharges during 60% of the eruptions listed by the JMA. This is significantly higher than for the World Wide Lightning Location Network, which detected electrical discharges (in the very low frequency range) within 20 kilometres of Sakurajima for less than 0.005% of the eruptions. Furthermore, the results show that for 40% of the detected eruptions, electrical discharges were detected before the estimated JMA timing. Hence, electrical discharges can mark the inception of the explosion with a higher precision and are an indication of ash emission. This demonstrates the value of the cost-effective sensors used here as a monitoring tool at active volcanoes.</p>

scholarly journals Dynamic cerebral autoregulation during passive heat stress in humans

2009 ◽  
Vol 296 (5) ◽  
pp. R1598-R1605 ◽  
Author(s):  
David A. Low ◽  
Jonathan E. Wingo ◽  
David M. Keller ◽  
Scott L. Davis ◽  
Jian Cui ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heat Stress ◽  
Transfer Function ◽  
High Frequency ◽  
Cerebral Autoregulation ◽  
Low Frequency ◽  
Passive Heating ◽  
Frequency Range ◽  
Very Low Frequency ◽  
Dynamic Cerebral Autoregulation

This study tested the hypothesis that passive heating impairs cerebral autoregulation. Transfer function analyses of resting arterial blood pressure and middle cerebral artery blood velocity (MCA Vmean), as well as MCA Vmean and blood pressure responses to rapid deflation of previously inflated thigh cuffs, were examined in nine healthy subjects under normothermic and passive heat stress (increase core temperature 1.1 ± 0.2°C, P < 0.001) conditions. Passive heating reduced MCA Vmean [change (Δ) of 8 ± 8 cm/s, P = 0.01], while blood pressure was maintained (Δ −1 ± 4 mmHg, P = 0.36). Coherence was decreased in the very-low-frequency range during heat stress (0.57 ± 0.13 to 0.26 ± 0.10, P = 0.001), but was >0.5 and similar between normothermia and heat stress in the low- (0.07–0.20 Hz, P = 0.40) and high-frequency (0.20–0.35 Hz, P = 0.12) ranges. Transfer gain was reduced during heat stress in the very-low-frequency (0.88 ± 0.38 to 0.59 ± 0.19 cm·s−1·mmHg−1, P = 0.02) range, but was unaffected in the low- and high-frequency ranges. The magnitude of the decrease in blood pressure (normothermia: 20 ± 4 mmHg, heat stress: 19 ± 6 mmHg, P = 0.88) and MCA Vmean (13 ± 4 to 12 ± 6 cm/s, P = 0.59) in response to cuff deflation was not affected by the thermal condition. Similarly, the rate of regulation of cerebrovascular conductance (CBVC) after cuff release (0.44 ± 0.22 to 0.38 ± 0.13 ΔCBVC units/s, P = 0.16) and the time for MCA Vmean to recover to precuff deflation baseline (10.0 ± 7.9 to 8.7 ± 4.9 s, P = 0.77) were not affected by heat stress. Counter to the proposed hypothesis, similar rate of regulation responses suggests that heat stress does not impair the ability to control cerebral perfusion after a rapid reduction in perfusion pressure, while reduced transfer function gain and coherence in the very-low-frequency range during heat stress suggest that dynamic cerebral autoregulation is improved during spontaneous oscillations in blood pressure within this frequency range.

Effects of Very Low Frequency Tones on Auditory Thresholds

1966 ◽  
Vol 9 (1) ◽  
pp. 150-160 ◽  
Author(s):  
J. Jerger ◽  
B. Alford ◽  
A. Coats ◽  
B. French
Keyword(s):  
Adverse Effects ◽  
Sound Pressure ◽  
Human Subjects ◽  
Low Frequency ◽  
Pressure Level ◽  
Variable Speed ◽  
Frequency Range ◽  
Auditory Thresholds ◽  
Very Low Frequency ◽  
Piston Cylinder

Nineteen human subjects were exposed to repeated three-minute tones in the sound pressure level range from 119 to 144 dB and the frequency range from 2–22 cps. The tones were produced in an acoustic test booth by a piston-cylinder arrangement, driven by a variable speed direct current motor. Eight subjects showed no adverse effects. Temporary threshold shifts (TTS) of 10 to 22 dB in the frequency range from 3 000 to 8 000 cps were observed in the remaining 11 subjects. In addition, the 7 and 12 cps signals produced considerable masking over the frequency range from 100 to 4 000 cps.

scholarly journals Further genetic diversification in multiple tumors and an evolutionary perspective on therapeutics

2015 ◽  
Author(s):  
Yong Tao ◽  
Zheng Hu ◽  
Shaoping Ling ◽  
Shiou-Hwie Yeh ◽  
Weiwei Zhai ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Drug Resistance ◽  
Low Frequency ◽  
Frequency Range ◽  
Resistance Mutations ◽  
Primary Tumors ◽  
Very Low Frequency ◽  
Evolutionary Forces ◽  
Single Tumor ◽  
Multiple Hepatocellular Carcinoma

The genetic diversity within a single tumor can be extremely large, possibly with mutations at all coding sites (Ling et al. 2015). In this study, we analyzed 12 cases of multiple hepatocellular carcinoma (HCC) tumors by sequencing and genotyping several samples from each case. In 10 cases, tumors are clonally related by a process of cell migration and colonization. They permit a detailed analysis of the evolutionary forces (mutation, migration, drift and natural selection) that influence the genetic diversity both within and between tumors. In 23 inter-tumor comparisons, the descendant tumor usually shows a higher growth rate than the parent tumor. In contrast, neutral diversity dominates within-tumor observations such that adaptively growing clones are rarely found. The apparent adaptive evolution between tumors can be explained by the inherent bias for detecting larger tumors that have a growth advantage. Beyond these tumors are a far larger number of clones which, growing at a neutral rate and too small to see, can nevertheless be verified by molecular means. Given that the estimated genetic diversity is often very large, therapeutic strategies need to take into account the pre-existence of many drug-resistance mutations. Importantly, these mutations are expected to be in the very low frequency range in the primary tumors (and become frequent in the relapses, as is indeed reported (1-3). In conclusion, tumors may often harbor a very large number of mutations in the very low frequency range. This duality provides both a challenge and an opportunity for designing strategies against drug resistance (4-8).

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