Major enhancement of extra-low-frequency radiation by increasing the high-frequency heating wave power in electrojet modulation

2002 ◽  
Vol 9 (1) ◽  
pp. 315-321 ◽  
Author(s):  
S. P. Kuo ◽  
S. H. Lee ◽  
Paul Kossey
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Wave Power ◽  
Frequency Radiation ◽  
Frequency Heating ◽  
Heating Wave

Generation of extra and very low-frequency (ELF/VLF) radiation by ionospheric electrojet modulation using high-frequency (HF) heating waves

2002 ◽  
Vol 68 (4) ◽  
pp. 267-284 ◽  
Author(s):  
S. P. KUO
Keyword(s):  
High Frequency ◽  
Thermal Instability ◽  
Loss Rate ◽  
Inelastic Collision ◽  
Modulation Frequency ◽  
Low Frequency ◽  
Heating Power ◽  
Very Low Frequency ◽  
Hf Heating ◽  
Heating Wave

Extra and very low-frequency (ELF/VLF) wave generation by modulated polar electrojet currents is studied numerically. Through Ohmic heating by the amplitude-modulated high-frequency heating wave, the conductivity and thus the current of the electrojet are modulated accordingly to set up the ionospheric antenna current. Stimulated thermal instability, which can further enhance the electrojet current modulation, is studied. It is first analysed analytically to determine the threshold heating power for its excitation. The nonlinear evolutions of the generated ELF/VLF waves enhanced by the instability are then studied numerically. Their spectra are also evaluated. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency in agreement with the Tromso observations. The efficiency enhancement by the stimulated thermal instability is hampered by inelastic collisions of electrons with neutral particles (mainly due to vibration excitation of N2), which cause this instability to saturate at low levels. However, the electron inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the heating power exceeds a threshold level, significant electron heating enhanced by the instability is shown, which indeed causes a steep drop in the electron inelastic collision loss rate. Consequently, this instability saturates at a much higher level, resulting to a near step increase (of about 10–13 dB depending on the modulation wave form) in the spectral intensity of ELF radiation. The dependence of the threshold power of the HF heating wave on the modulation frequency is determined.

Investigating Thunderstorm HF/VHF Radio Bursts with Weak Lower Frequency Radiation

2020 ◽  
Author(s):  
Ningyu Liu ◽  
Joseph Dwyer
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Strong Field ◽  
Large Fraction ◽  
Low Frequency ◽  
Very High Frequency ◽  
Lightning Initiation ◽  
Study Support ◽  
Volcanic Lightning ◽  
Frequency Radiation

<p>While the spectrum of lightning electromagnetic radiation is known to peak around 5-10 kHz in the very low frequency (VLF) range, intense high frequency/very high frequency (HF/VHF) radiation can be produced by various lightning related processes. In fact, thunderstorm narrow bipolar events (NBEs), which are capable of initiating lightning, are the most powerful HF/VHF sources in nature on Earth. But even for NBEs, the spectral intensity in HF/VHF is still many orders of magnitude weaker than that of lower frequencies (Liu et al., JGR, 124, https://doi.org/10.1029/2019JD030439, 2019). HF/VHF bursts with weak VLF signals, however, can also be produced by thunderstorms. These bursts may be related to the thunderstorm precursor events noted by Rison et al. (Nat. Commun., 7, 10721, 2016) and are also found to precede a large fraction of lightning initiation (Lyu et al., JGR, 124, 2994, 2019). They are also known as continual radio frequency (CRF) radiation associated with volcanic lightning (Behnke et. al., JGR, 123, 4157, 2018).</p><p> </p><p>In this talk, we report a theoretical and modeling study to investigate a physical mechanism for production of those HF/VHF bursts. The study is built on the theory developed recently concerning the radio emissions from an ensemble of streamers (Liu et al., 2019). We find an ensemble of streamer discharges that develop in random directions can produce HF/VHF radiation with intensity comparable to those all developing in a single direction, but the VLF intensity is many orders of magnitude weaker. The results of our study support the conclusions of Behnke et. al (2018) that CRF is produced in the absence of large-scale electric field, it results in insignificant charge transfer, and it is caused by streamers. In the context of the HF/VHF bursts preceding lightning initiation (Lyu et. al, 2019), our results imply that highly localized strong field regions exist in thunderstorms and streamers take place in those regions, which somehow precondition the medium for lightning initiation.</p>

Estimating the Areas of High-Frequency Wave Radiation on the Fault Plane of the 2008 Mw 7.9 Wenchuan, China, Earthquake by Envelope Inversion

2021 ◽  
Author(s):  
Deyu Yin ◽  
Yun Dong ◽  
Qifang Liu ◽  
Jingke Wu ◽  
Huasheng Sun ◽  
...  
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
Low Frequency ◽  
Rupture Process ◽  
Wave Radiation ◽  
Frequency Wave ◽  
High Frequency Wave ◽  
Initial Rupture ◽  
High Frequency Waves ◽  
Frequency Radiation

ABSTRACT We estimated the areas exhibiting high-frequency (1∼10  Hz) wave radiation on the fault plane of the 2008 Wenchuan earthquake, by applying envelope inversion to strong-motion acceleration records. The corrected records of two small earthquakes are adopted as the empirical Green’s functions. Considering the change in the rupture pattern of the Wenchuan earthquake from southwest to northeast, the records of small earthquakes dominated by thrust and strike-slip are utilized as the empirical Green’s function for the southwestern and northeastern fault sections, respectively. The results are as follows: (1) According to the high-frequency wave radiation, the rupture process is complex. High-frequency waves radiated strongly in six areas: around the initial rupture point, along the north and south edges of the fault plane, near the area of intersection with the cross-cutting Xiaoyudong fault, south of Nanba, and near the area of Qingchuan. In total, these areas can be divided into three cases. In the first situation, high-frequency waves radiated strongly around the initial rupture area, which may be associated with the initiation of rupture and a high stress drop. The second location is near the periphery of the fault, which is associated with the termination of rupture. The third condition comprises high-frequency waves near the intersection with the cross-cutting Xiaoyudong fault. This area as a geometric barrier, and the surface rupture is observed. (2) The distribution patterns of the high- and low-frequency radiation intensity differ on the fault plane. From the hypocenter to the point of intersection with the Xiaoyudong fault, the high-frequency wave is located around the area with large slip value. In other areas, the distribution of the high- and low-frequency radiation is no obvious relationship. This different characteristic indicates the complexity of the rupture process.

Behavioral Effects of Stimulation by UHF Radio Fields

1965 ◽  
Vol 17 (2) ◽  
pp. 595-602 ◽  
Author(s):  
Susan Korbel Eakin ◽  
William D. Thompson
Keyword(s):  
High Frequency ◽  
Gradual Increase ◽  
Low Frequency ◽  
Audiogenic Seizures ◽  
Behavioral Effects ◽  
Albino Rats ◽  
Radio Waves ◽  
Frequency Radiation ◽  
Electroshock Convulsion

20 male albino rats were used as Ss in determining behavioral effects of ultra high frequency radiation. Experimental Ss were exposed to low intensity (50,000 mV), low frequency (300 mc to 920 mc) UHF radio waves for 47 consecutive days. Radiated rats were more active than non-radiated rats during the early part of the experiment, but became less active as the days of radiation increased. The UHF group was more emotional than the non-UHF group and showed a gradual increase in the latency of recovery from electroshock convulsion. No differences were found for weight, audiogenic seizures, and water consumption. Results suggest that (a) some time is required for UHF to have a consistent effect on behavior, and (b) the effects on behavior may be non-thermal and related to neurophysiological substrates.

scholarly journals Fine Structure in Type IV Solar Radio Bursts

1974 ◽  
Vol 57 ◽  
pp. 291-292
Author(s):  
C. Caroubalos ◽  
M. Pick ◽  
C. Chiuderi ◽  
R. Giachetti ◽  
H. Rosenberg ◽  
...  
Keyword(s):  
Fine Structure ◽  
High Frequency ◽  
Solar Radio ◽  
Low Frequency ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
Type Iv ◽  
Low Frequency Oscillations ◽  
Solar Type ◽  
Frequency Radiation

(Solar Phys.). The fine structure in solar type IV radio bursts was studied using the 169 MHz Nançay radioheliograph and the 60 channel radiospectrograph at Utrecht (160–320 MHz). The observed fine structure includes pulsating structure, zebra patterns (parallel drifting bands) and intermediate drift bursts. All are considered as modulation of high frequency radiation by low frequency oscillations or as the result of up conversion of low frequency oscillations to higher frequencies (Rosenberg, 1973).

Sign in / Sign up

Export Citation Format

Share Document