Controlled precipitation of radiation belt electrons whistler-mode waves. by Prajwal Kulkarni

ISBN: 9781109077070

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106 pages


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Controlled precipitation of radiation belt electrons  by  whistler-mode waves. by Prajwal Kulkarni

Controlled precipitation of radiation belt electrons by whistler-mode waves. by Prajwal Kulkarni
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This dissertation presents results and analysis regarding the use of anthropogenic ground-based and space-based Very Low Frequency (VLF) transmitters to precipitate energetic electrons in the inner radiation belt. While existing ground-based VLFMoreThis dissertation presents results and analysis regarding the use of anthropogenic ground-based and space-based Very Low Frequency (VLF) transmitters to precipitate energetic electrons in the inner radiation belt.

While existing ground-based VLF transmitters already precipitate energetic electrons, they do so inadvertently. In this work, we consider sources designed specifically for the purpose of precipitating >100 keV electrons. This concept is termed controlled precipitation. We focus on this energy range because these electrons are most damaging from a so-called space weather perspective.-We initially consider the distribution of whistler-mode wave energy from space-based sources distributed in L-shell and geomagnetic latitude.

We also incorporate the effects of VLF antenna radiation immersed in a magnetoplasma. Our results demonstrate that a space-based source, by varying the frequency of the injected waves, can target L-shells both higher and lower than the source site, with wave frequencies below (above) the local lower hybrid resonance frequency moving to higher (lower) L-shells.

We show that only three sources placed at various locations in the inner magnetosphere are required to project wave power over the range 1.4≤L≤2.7, which comprises the bulk of the inner radiation belt. We also calculate the energetic electron precipitation that would be induced by waves injected by such sources. The waves injected by space-based sources propagate with highly oblique wave normal angles close to the local resonance cone. In contrast with previous analysis, we show that these waves do induce substantial >1 MeV electron precipitation.

Compared to a single-pass interaction, highly oblique magnetospherically reflecting whistler-mode waves precipitate up to 16 times more 100 keV to 5 MeV electrons. Waves injected at initial wave normal angles closer to the magnetic field, e.g., 45°, in fact precipitate fewer >1 MeV electrons than waves injected close to the resonance cone.-We also investigate the tradeoffs among source location, operating frequency and radiated power for ground-based VLF sources designed to precipitate energetic electrons in the inner radiation belts.

We determine energetic electron precipitation signatures induced by five existing ground-based VLF sources as well as five different hypothetical transmitters distributed broadly in geomagnetic latitude with a wide range of operating frequencies. We show that source location affects induced precipitation more strongly than operating frequency or radiated power. Sources located at 35° to 45° induce the most >100 keV precipitation for the 10 to 40 kHz waves typical of ground-based VLF sources, while locations below lambda&sime-15° or above lambda&sime-55° are least effective at precipitating energetic electrons.

In all cases, induced precipitation increases as the operating frequency decreases, with 10 kHz waves from a source at lambda&sime-35° the most effective at precipitating >100 keV electrons. Precipitation signatures produced by five existing ground-based VLF transmitters are also simulated: the NAA, NLK, NAU, NPM, and NWC VLF transmitters.

Among these, the NWC transmitter located at a geomagnetic latitude of 31.7° in western Australia induces the strongest >100 keV electron precipitation signature, followed by the NPM, NAU, NAA and NLK transmitters.



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