Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 128
Book Description
Magnetospheric growth of coherent VLF signals transmitted from Siple Station, Antarctica is inhibited by whistler mode echoes of earlier transmitter signals. This new phenomenon, called echo-induced suppression, is observed at least a third of the time that transmissions from Siple Station are detected at the receiving station in Roberval, Quebec, Canada. Suppression levels as high as 20 dB are observed. Though the echo is usually much weaker than the direct signal the level of suppression is directly related to the amplitude of the echo. The echoes reduce triggering of emissions as well as the growth of the signal. Echo-induced suppression is not explained by linear wave-wave interference. The echoes are thought to restrict growth by reducing the coherence of the total input signal. According to quasi-linear theory, wave growth is regulated by changes in the particle pitch angle distribution that results from wave-particle interaction. These new results suggest that coherent waves tend to limit their own growth, even when modification of the particle pitch angle distribution is unimportant. Other phenomena such as whistler-induced suppression of signal growth are thought to be related to echo-induced suppression. Wave-induced growth suppression provides an indirect verification of the existence of discrete ducts for the propagation of VLF signals in the magnetosphere.
Suppression Effects Associated with VLF Transmitter Signals Injected Into the Magnetosphere
Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 128
Book Description
Magnetospheric growth of coherent VLF signals transmitted from Siple Station, Antarctica is inhibited by whistler mode echoes of earlier transmitter signals. This new phenomenon, called echo-induced suppression, is observed at least a third of the time that transmissions from Siple Station are detected at the receiving station in Roberval, Quebec, Canada. Suppression levels as high as 20 dB are observed. Though the echo is usually much weaker than the direct signal the level of suppression is directly related to the amplitude of the echo. The echoes reduce triggering of emissions as well as the growth of the signal. Echo-induced suppression is not explained by linear wave-wave interference. The echoes are thought to restrict growth by reducing the coherence of the total input signal. According to quasi-linear theory, wave growth is regulated by changes in the particle pitch angle distribution that results from wave-particle interaction. These new results suggest that coherent waves tend to limit their own growth, even when modification of the particle pitch angle distribution is unimportant. Other phenomena such as whistler-induced suppression of signal growth are thought to be related to echo-induced suppression. Wave-induced growth suppression provides an indirect verification of the existence of discrete ducts for the propagation of VLF signals in the magnetosphere.
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 128
Book Description
Magnetospheric growth of coherent VLF signals transmitted from Siple Station, Antarctica is inhibited by whistler mode echoes of earlier transmitter signals. This new phenomenon, called echo-induced suppression, is observed at least a third of the time that transmissions from Siple Station are detected at the receiving station in Roberval, Quebec, Canada. Suppression levels as high as 20 dB are observed. Though the echo is usually much weaker than the direct signal the level of suppression is directly related to the amplitude of the echo. The echoes reduce triggering of emissions as well as the growth of the signal. Echo-induced suppression is not explained by linear wave-wave interference. The echoes are thought to restrict growth by reducing the coherence of the total input signal. According to quasi-linear theory, wave growth is regulated by changes in the particle pitch angle distribution that results from wave-particle interaction. These new results suggest that coherent waves tend to limit their own growth, even when modification of the particle pitch angle distribution is unimportant. Other phenomena such as whistler-induced suppression of signal growth are thought to be related to echo-induced suppression. Wave-induced growth suppression provides an indirect verification of the existence of discrete ducts for the propagation of VLF signals in the magnetosphere.
Scientific and Technical Aerospace Reports
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1102
Book Description
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 1102
Book Description
VLF Wave-wave Interaction Experiments in the Magnetosphere
Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 222
Book Description
Publisher:
ISBN:
Category : Magnetosphere
Languages : en
Pages : 222
Book Description
Antarctic Journal of the United States
Author:
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 26
Book Description
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 26
Book Description
Annual Report for Fiscal Year ...
Author: National Science Foundation (U.S.)
Publisher:
ISBN:
Category : Research
Languages : en
Pages :
Book Description
Publisher:
ISBN:
Category : Research
Languages : en
Pages :
Book Description
The Effects of Ground-based Very Low Frequency Transmitters on the Ionosphere and Magnetosphere
Author: Kevin Graf
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The effects of ground-based very low frequency (VLF) transmitters on the ionosphere and magnetosphere are investigated. VLF transmitters, used primarily for Naval communications with submarines, are also capable of heating the ionosphere and inducing the precipitation of energetic electrons from the Earth's radiation belts. Controlled modulation experiments are performed with the 21.4 kHz, 424 kW VLF transmitter NPM in Lualualei, Hawaii, and physical effects of the NPM transmissions are studied with sub-ionospherically propagating VLF probe signals. Observed perturbations to the probe signal are not consistent with expectations from transmitter-induced electron precipitation nor to off-path scattering from a concentrated heating region near the transmitter but rather appear to be the result of scattering from extended lateral heating of the ionosphere by the NPM transmitter. A large-scale computational modeling framework confirms theoretically that this form of ionospheric heating can account for the observed probe signal modulations, establishing that the lateral extent of ionospheric heating due to VLF transmitters is several thousand kilometers, significantly greater than previously recognized. The trans-ionospheric propagation of VLF waves is also investigated as updated attenuation estimates are provided for multiple scenarios.
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The effects of ground-based very low frequency (VLF) transmitters on the ionosphere and magnetosphere are investigated. VLF transmitters, used primarily for Naval communications with submarines, are also capable of heating the ionosphere and inducing the precipitation of energetic electrons from the Earth's radiation belts. Controlled modulation experiments are performed with the 21.4 kHz, 424 kW VLF transmitter NPM in Lualualei, Hawaii, and physical effects of the NPM transmissions are studied with sub-ionospherically propagating VLF probe signals. Observed perturbations to the probe signal are not consistent with expectations from transmitter-induced electron precipitation nor to off-path scattering from a concentrated heating region near the transmitter but rather appear to be the result of scattering from extended lateral heating of the ionosphere by the NPM transmitter. A large-scale computational modeling framework confirms theoretically that this form of ionospheric heating can account for the observed probe signal modulations, establishing that the lateral extent of ionospheric heating due to VLF transmitters is several thousand kilometers, significantly greater than previously recognized. The trans-ionospheric propagation of VLF waves is also investigated as updated attenuation estimates are provided for multiple scenarios.
Government Reports Announcements & Index
Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 1488
Book Description
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 1488
Book Description
Semi-annual Status Report No.132, January Through June 1977
Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category :
Languages : en
Pages : 140
Book Description
Publisher:
ISBN:
Category :
Languages : en
Pages : 140
Book Description
Antarctic Bibliography
Author:
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 652
Book Description
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 652
Book Description
Current Antarctic Literature
Author:
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 414
Book Description
Publisher:
ISBN:
Category : Antarctica
Languages : en
Pages : 414
Book Description