Full-wave VLF modes in a cylindrically symmetric enhancement of plasma density |
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| Authors: | M J Laird D Nunn |
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| Institution: | Dept. of Mathematics, King's College, London WC2, England |
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| Abstract: | VLF waves in the magnetosphere may be guided by ducts, i.e. enhancements of plasma density aligned with the geomagnetic field. It is required to account for the good transmission properties of these ducts as some leakage of energy is expected, with consequent attenuation. We consider a cylindrical duct, whose axis is parallel to a uniform magnetic field. The electron density of a cold plasma is a function only of radial distance r from the axis, taking constant values in inner and outer regions r < a and r > b, and varying smoothly in the duct wall a < r < b. We compute full-wave ‘trapped’ VLF modes. Results are presented for a range of values of the parameters of the model. In general we find that attenuation of leading modes is very low, agreeing with observation. Specific features are that leakage (arising from mode conversion in the duct wall) increases as the wall is made thinner, that leakage for the leading modes is less for weaker ducts, that many modes may propagate, and that, because of interference effects, some higher order modes also suffer little attenuation. |
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