Trimpi perturbations from large ionisation enhancement patches

Nunn, D.; Strangeways, H.J.

doi:10.1016/s1364-6826(00)00004-3

Cited by 6 publications

(14 citation statements)

References 34 publications

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“…The time‐varying electron number density altitude profiles were applied to the subionospheric VLF wave propagation code MODEFNDR combined with linear scattering theory [e.g., Nunn and Strangeways , 2000; Rodger et al , 2004]. VLF propagation from the source transmitter to a 3‐D spatial grid used to model the modified region is computed using modal theory and the Naval Ocean Systems Center (NOSC; San Diego, USA) MODEFNDR code [ Morfitt and Shellman , 1976].…”

Section: Monoenergetic Beam Vlf Perturbationsmentioning

confidence: 99%

Storm time, short‐lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation

et al. 2007

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[1] In this study we report on ground-based observations of short bursts of relativistic electron precipitation (REP), detected by a subionospheric propagation sensor in Sodankylä, Finland during 2005. In two $4 hour case study periods from L = 5.2, around local midnight, several hundred short-lived radio wave perturbations were observed, covering a wide range of arrival azimuths. The vast majority ($99%) of these perturbations were not simultaneous with perturbations on other paths, consistent with a precipitation ''rainstorm'' producing ionospheric changes of small spatial sizes around the Sodankylä receiver. The recovery time of these radio wave perturbations are $1.2 s, which is consistent with the modeled effects of a burst of >2 MeV precipitating electrons. This agrees with satellite observations of the microburst energy spectrum. The energetic nature of the precipitation which produces the FAST perturbations suggests that they should be observable in both day and night conditions. While it is widely assumed that satellite-detected REP microbursts are due to wave-particle interactions with very low-frequency chorus waves, the energy spectra predicted by our current models of chorus propagation and wave-particle interaction are not consistent with the experimentally observed radio wave perturbations presented here or previously reported satellite observations of REP microbursts. The results inferred from both the satellite and subionospheric observations, namely the absence of a large, dominant component of <100 keV precipitating electrons, fundamentally disagrees with a mechanism of chorusdriven precipitation. Nonetheless, further work on the modeling of chorus-driven precipitation is required.Citation: Rodger, C. J., M. A. Clilverd, D. Nunn, P. T. Verronen, J. Bortnik, and E. Turunen (2007), Storm time, short-lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation,

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Section: Monoenergetic Beam Vlf Perturbationsmentioning

confidence: 99%

Storm time, short‐lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation

et al. 2007

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“…A number of theoretical studies have made use of electron density perturbations with a vertical Gaussian profile to represent the WEP produced ionospheric electron density modification (Nunn and Strangeways, 2000;Clilverd et al, 2002), while others have studied modifications derived from satellite observed WEP fluxes (e.g. Pasko and Inan, 1994;Rodger et al, 2002).…”

Section: Introductionmentioning

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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“…Determining the typical size of LEP patches would allow the calculation of electron precipitation fluxes following wave‐particle interactions [ Nunn and Strangeways , 2000]; input into modeling the dimensions of plasmaspheric ducts [ Strangeways , 1999]; and investigation of the possibility of oblique (nonducted) whistler‐induced precipitation [ Lauben et al , 1999; Johnson et al , 1999].…”

Section: Introductionmentioning

confidence: 99%

“…However, some of the events observed in that study were consistent with smooth lateral spread, but the remainder required fine structure to explain the observed diffraction patterns. The interpretation of the results of these early studies were made more complex by the realisation that non‐LEP Trimpi (some of which appear to be associated with red sprites) were contaminating the studies [ Rodger , 1999; Nunn and Strangeways , 2000].…”

Section: Introductionmentioning

confidence: 99%

Determining the size of lightning‐induced electron precipitation patches

et al. 2002

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We analyze Trimpi signatures during 23 and 24 April 1994 at four sites on or near the Antarctic Peninsula (Palmer, Faraday, Rothera, and Halley) on subionospheric VLF signals received from four U.S. naval transmitters (NAA, NSS, NLK, and NPM). Electron precipitation patches are found to be large, i.e., ∼1500 km × 600 km, with the longer axis orientated east‐west. Calculations using a three‐dimensional Born scattering model, where patch densities are 1.5 electrons cm−3 above ambient at the center at ∼84 km altitude, provides results that are consistent with this picture. A high proportion (38%) of the Trimpi events were associated with strong lightning flashes in eastern United States. When lightning discharges had currents >65 kA (positive or negative), there was a >80% chance of seeing an associated Trimpi event. The chance of seeing any Trimpi events fell to near zero for discharges of <45 kA. The largest Trimpi perturbations occur when the center of the precipitation patch is 700–800 km from the receivers. This result is consistent with the modeling calculations for large patches. The equatorward edge of the precipitation patch was estimated to be at ∼60°S, close to the magnetic conjugate of the lightning. The close association of the equatorward edge of the precipitation patch with the conjugate location of the causative lightning is consistent with a quasi‐ducted whistler‐induced precipitation mechanism. Nonducted whistler‐induced precipitation mechanisms would predict a 5°–10° latitudinal gap between the lightning and the equatorward edge of the patch. However, the lack of observed whistlers at the time of the Trimpi events is consistent with the nonducted whistler mechanism and is not consistent with the quasi‐ducted mechanism, although the distances from duct exit point to receiver may have been too large (∼700–1000 km) for the signals to be detectable. Using the significantly larger patch dimensions determined in this study, it is estimated that lightning may well be 10–100 times more effective at depleting the radiation belts than hiss.

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Trimpi perturbations from large ionisation enhancement patches

Cited by 6 publications

References 34 publications

Storm time, short‐lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation

Storm time, short‐lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation

Investigating radiation belt losses though numerical modelling of precipitating fluxes

Determining the size of lightning‐induced electron precipitation patches

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