An experiment on the threshold effect in the coherent wave instability

Mielke, T. A.; Helliwell, R. A.

doi:10.1029/92gl02179

Cited by 4 publications

(1 citation statement)

References 11 publications

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“…Figure 2 shows an example of VLF emissions triggered in the plasmasphere by fixed frequency signals from the Siple Station ELF/VLF transmitter [ Helliwell and Katsufrakis , 1974]. The instability of the plasma which gives rise to the emissions is known as the “coherent wave instability” (CWI) because the emissions are triggered only when a coherent ELF/VLF input wave is present as the triggering signal [ Mielke and Helliwell , 1992]. In general triggered emissions such as these within the plasmasphere closely resemble many chorus emissions triggered outside the plasmasphere [e.g., Pickett et al , 2004].…”

Section: Commonalities Of Three Emission Typesmentioning

confidence: 99%

Source regions of banded chorus

Bell

Inan

Haque

et al. 2009

Geophysical Research Letters

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ELF/VLF chorus emissions are very intense electromagnetic plasma waves that are naturally and spontaneously excited near the magnetic equatorial plane outside the plasmasphere during periods of magnetic disturbance. These emissions are believed to play an important role in the acceleration of 10 to 100 keV radiation belt electrons to MeV energies during the disturbed time periods. Spacecraft observations near the magnetic equatorial plane in the regions where chorus emissions are generated show that the chorus often appears in two distinct frequency bands, one band below fce/2 and one band above fce/2, where fce is the local electron gyrofrequency. This configuration is known as banded chorus. In the present paper we show that this type of configuration can be readily explained if it is assumed that the chorus is excited in ducts of either enhanced or depleted cold plasma density.

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Section: Commonalities Of Three Emission Typesmentioning

confidence: 99%

Source regions of banded chorus

Bell

Inan

Haque

et al. 2009

Geophysical Research Letters

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Whistler-mode wave-injection experiments in the plasmasphere with a radio sounder

Sonwalkar

Harikumar

et al. 2001

Journal of Atmospheric and Solar-Terrestrial Physics

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Properties of the magnetospheric hot plasma distribution deduced from whistler mode wave injection at 2400 Hz: Ground‐based detection of azimuthal structure in magnetospheric hot plasmas

Sonwalkar¹,

Carpenter²,

Helliwell³

et al. 1997

J. Geophys. Res.

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Siple station VLF wave injection experiments aimed at finding the properties of the magnetospheric hot plasma were conducted for a 9‐hour period between 1705 and 0210 UT on January 23–24, 1988. A special frequency versus time format, lasting l min and transmitted every 5 min, consisted of a sequence of pulses, frequency ramps, and parabolas, all in a 1‐kHz range centered on 2400 Hz. The transmitted signals, after propagating along a geomagnetic field‐aligned duct, were recorded at Lake Mistissini, Canada. At various times during the 9‐hour interval the Siple signals showed features characteristic of wave‐particle interactions, including wave growth, sidebands, and triggered emissions. Our observations, primarily at 2400 Hz, show that (1) there were no correlations between the initial levels, the growth rates, and the saturation levels of constant‐frequency pulses; (2) in general, the values of growth rate and saturation level of two pulses injected within 30 s were nearly the same; (3) the initial level, growth rate, and saturation level showed temporal variations over 5–15 min and 1–2 hour timescales; (4) the leading edges of constant‐frequency signals underwent spatial amplification; and (5) under conditions of saturation the received signal bandwidth (∼ 20 Hz) remained constant over a 1‐hour period, although the saturation level and growth rate varied during the same period. On the assumption that gyroresonant interactions were responsible for the observed wave growth and saturation, the timescales over which those phenomena varied provide constraints on the possible energetic electron population within the duct. In the reference frame of the duct (L ∼ 5.1, Ne ∼ 280 cm−3) the particle fluxes showed no variation over a 30‐s timescale but varied over 5–15 min and 1–2 hour timescales. The 5–15 min timescale variations indicate longitudinal structures ranging from ∼ 0.2° or ∼100 km (in the equatorial plane) for electrons with energy E = 0.6 keV and pitch angle α = 40°, to ∼ 5° or ∼2800 km for electrons with energy E = 11 keV and pitch angle α = 80°. The hour‐long time variations indicate longitudinal structures ranging from ∼ 2° or ∼1100 km (in the equatorial plane) for electrons with energy E = 0.6 keV and pitch angle α = 40°, to ∼ 45° or ∼25,000 km for electrons with energy E = 11 keV and pitch angle α = 80°. We conclude that ground‐based active and passive wave experiments have substantial potential for investigating properties of the hot plasma of the magnetosphere.

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An experiment on the threshold effect in the coherent wave instability

Cited by 4 publications

References 11 publications

Source regions of banded chorus

Source regions of banded chorus

Whistler-mode wave-injection experiments in the plasmasphere with a radio sounder

Properties of the magnetospheric hot plasma distribution deduced from whistler mode wave injection at 2400 Hz: Ground‐based detection of azimuthal structure in magnetospheric hot plasmas

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