VLF Trimpi modelling on the path NWC-Dunedin using both finite element and 3D Born modelling

Nunn, D.; Baba, Kiyohide; Hayakawa, M.

doi:10.1016/s1364-6826(98)00088-1

Cited by 16 publications

(13 citation statements)

References 27 publications

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“…Clearly, for large LIE patches and/or patches with large changes in electron number density the Born approximation will break down, since the total field at a point in the LIE will not be well approximated by the zeroorder incident field. By comparing with a 2-D Finite Element modelling of VLF scattering, it was shown in Nunn et al (1998) that for an LIE with horizontal dimensions ∼100 km the Born approximation fails for maximum electron density perturbations >6 el. cm −3 .…”

Section: Scattering Theory and Implementationmentioning

confidence: 99%

Investigating radiation belt losses though numerical modelling of precipitating fluxes

2004

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Abstract. It has been suggested that whistler-induced electron precipitation (WEP) may be the most significant inner radiation belt loss process for some electron energy ranges. One area of uncertainty lies in identifying a typical estimate of the precipitating fluxes from the examples given in the literature to date. Here we aim to solve this difficulty through modelling satellite and ground-based observations of onset and decay of the precipitation and its effects in the ionosphere by examining WEP-produced Trimpi perturbations in subionospheric VLF transmissions. In this study we find that typical Trimpi are well described by the effects of WEP spectra derived from the AE-5 inner radiation belt model for typical precipitating energy fluxes. This confirms the validity of the radiation belt lifetimes determined in previous studies using these flux parameters. We find that the large variation in observed Trimpi perturbation size occurring over time scales of minutes to hours is primarily due to differing precipitation flux levels rather than changing WEP spectra. Finally, we show that high-time resolution measurements during the onset of Trimpi perturbations should provide a useful signature for discriminating WEP Trimpi from non-WEP Trimpi, due to the pulsed nature of the WEP arrival.

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Section: Scattering Theory and Implementationmentioning

confidence: 99%

Investigating radiation belt losses though numerical modelling of precipitating fluxes

2004

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“…Clearly for large LIE patches and/or patches with large dN e the Born approximation will break down, since the total ®eld at a point in the LIE will not be well approximated by the zero order incident ®eld. Using a 2D Finite Element modelling of VLF scattering it was shown in Nunn et al (1998) and Baba et al (1998) that for an LIE with horizontal dimensions H100 km the Born approximation fails for maximum electron density perturbations >6 el/cc. The dominant cause of non-Born behaviour is the progressive exclusion of the incident ®eld from the interior of the LIE due to the classic and well known skin depth eect.…”

Section: Scattering Theory and Implementationmentioning

confidence: 99%

“…These were considered to arise from mode conversion and subsequent multiple mode propagation. Comparison between calculations using their FEM treatment and a 3D code that invokes the Born approximation was made by Nunn et al (1998). The results from the two computations showed excellent agreement.…”

Section: Introductionmentioning

confidence: 99%

Trimpi perturbations from large ionisation enhancement patches

Nunn

Strangeways

2000

Journal of Atmospheric and Solar-Terrestrial Physics

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A number of increasingly sophisticated and realistic models have been developed in order to investigate the interaction between sub-ionospherically propagating VLF waves and regions of ionisation enhancement (LIE 1 ) in the D-region caused by lightning-induced electron precipitation enhancements (LEP). This LEP-produced LIE can result in phase and amplitude perturbations on received VLF radio signals that are referred to as Trimpis or more precisely, classic Trimpis, to distinguish them from``early/fast Trimpis'' or``VLF sprites'' which are not caused by LEP and are not considered here. It is important, for comparison with experimentally observed Trimpi eects, that the spatial extent of the D-region electron density (N e ) perturbation is modeled accurately. Here, it is argued that most previous modeling has used patch (LIE) sizes that are typically up to 100 km in both latitudinal and longitudinal extent, which are generally smaller than those that actually occur for real lightning induced electron precipitation events. It would also appear that maximum DN e values assumed have often been too large, and the patches (LIEs) have been incorrectly modelled as circular rather than elliptical in horizontal extent. Consequently, in the present work, Trimpi perturbations are determined for LIEs with smaller maximum DN e , larger spatial extent and elliptical shape. Calculations of VLF Trimpis have been made as a function of the horizontal coordinates of the LIE centre, over the whole rectangular corridor linking transmitter and receiver. The Trimpi modelling program is fully 3D, and takes account of modal mixing at the LIE. The underlying theory assumes weak Born scattering, but the code calculates a non-Born skin depth attenuation function for the LIE in question. The LIE is modelled as an electron density enhancement with a Gaussian pro®le in all coordinates. Results for a large elliptical LIE H 200 Â 600 km show that signi®cant Trimpis, HÀ0.4 dB in amplitude and H+48 in phase are predicted, using modest maximum DN e values H 1.5 el/cc. Such an electron density enhancement is well within the range that would be expected to result from experimentally observed¯uxes of electron precipitation following wave particle interactions with whistler-mode waves. 7

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“…Later the non-Born method was developed by Baba and Hayakawa(1996) by using the FEM, though this was two-dimensional (14) . Then, Nunn et al (1998) compared the 3D Born approximation with the non-Born method to validate the limitation of each method (15) . The VLF scattering from the ionospheric perturbations associated with elves is found to be relatively weak.…”

Section: Mesospheric Optical Phenomena Associated With Lightning Discmentioning

confidence: 99%

Natural Electromagnetic Phenomena and Electromagnetic Theory: A Review

2004

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We review the new findings on natural electromagnetic phenomena in the near-Earth environment and will show the importance of electromagnetic analyses in elucidating the essential points of these phenomena. The topics include (1) atmospheric phenomena related to lightning (e.g. mesospheric optical emissions); (2) seismo-electromagnetic phenomena (electromagnetic phenomena associated with earthquakes and/or volcano eruptions); (3) plasma and wave phenomena in the Earth's ionosphere and magnetosphere; and (4) electromagnetic or electrodynamic coupling among different regions. We pay our greatest attention to the unsolved essential problems for each subject, and suggest how electromagnetics would contribute to a solution to those problems.

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VLF Trimpi modelling on the path NWC-Dunedin using both finite element and 3D Born modelling

Cited by 16 publications

References 27 publications

Investigating radiation belt losses though numerical modelling of precipitating fluxes

Investigating radiation belt losses though numerical modelling of precipitating fluxes

Trimpi perturbations from large ionisation enhancement patches

Natural Electromagnetic Phenomena and Electromagnetic Theory: A Review

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