Phase and amplitude perturbations observed on subionospheric VLF signal recorded at Varanasi (L = 1.07) using SoftPAL Receiver
20 Oct 2011-pp 1-4
TL;DR: In this paper, phase and amplitude perturbations in VLF signal propagating in the Earth-ionosphere waveguide, monitored at low latitude station Varanasi using SoftPAL Receiver are reported.
Abstract: We report here preliminary observations of phase and amplitude perturbations in VLF signal propagating in the Earth-ionosphere waveguide, monitored at low latitude station Varanasi using SoftPAL Receiver. Phase and amplitude perturbations (trimpis) on VLF signals consists of a sudden change in phase and amplitude of the transmitter signal followed by a slow recovery to the initial levels as the ionization decays. The current understanding of lightening discharge associated processes that leads to the changes in the characteristic of the waveguide and thus variation in the received amplitude and/or phase of the VLF transmission signals have been reported.
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01 Feb 1975
TL;DR: In this paper, the authors used pitch angle diffusion into the loss cone driven by the cyclotron resonant interaction to estimate the lifetime of inner-zone electrons, which ranges between 10 and 60 days.
Abstract: Broad band incoherent electromagnetic waves, called hiss, have been detected in the inner zone magnetosphere (L 10−6 γ²/Hz at the start of storm recovery phases, 10−7 – 10−6 γ²/Hz during substorms, and 0.4 to >3.1 MeV from L = 2 to L = 1.1, respectively. Characteristic lifetimes of inner zone electrons, calculated in order of magnitude fashion on the basis of pitch angle diffusion into the loss cone driven by the cyclotron resonant interaction, are found to range between 10 and 60 days. These computed lifetimes are consistent with observations of enhanced electron precipitation for L > 1.25 during storms. Although Coulomb scattering appears to be the dominant loss mechanism for L < 1.25, pitch angles scattering by the hiss may make a significant contribution to electron losses, especially during magnetically active intervals. The source of inner zone hiss has also been investigated. Two possible mechanisms of locally generating hiss in the inner zone, an electron cyclotron instability and a Landau resonance, are studied but are found to be unlikely candidates to give rise to hiss. Most features of inner zone hiss can be explained by the hypothesis that hiss originates in the vicinity of the plasmapause as plasmaspheric hiss, which is then able to propagate into the inner zone. There are two major effects that will allow this to occur during storms and substorms. The first is the intensification of plasmaspheric hiss as the freshly injected electrons convect and drift across the plasmapause into the high-density plasmasphere, leading to cyclotron instability. The second is the displacement of the plasmapause, and the presumed source region, to low L values during strong magnetic activity. This reduces the length of the ray paths leading to the inner zone and hence the amount of Landau damping. The present observations are compared with this propagation model and the two are found to be in good agreement.
95 citations
References
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TL;DR: In this paper, the amplitude of long-distance subionospheric VLF transmissions were found at night in association with whistlers, and both increases and decreases in signal strength were observed, depending on signal frequency and the receiving antenna.
Abstract: Sudden changes in the amplitude of long-distance subionospheric VLF transmissions were found at night in association with whistlers. Both increases and decreases in signal strength were observed, depending on signal frequency and orieniation of the receiving antenna. Sample observations at Eights Station in Antarctica of station NSS (Annapolis, Maryland) on 22.3 kHz showed increases in signal strength that averaged 3 db, with rise times of about 2 sec and durations of about 30 sec. Coincident with every rise was a midlatitude (L approximately 2.5) whistler originating in the northern hemisphere. To explain this association, it is suggested that the whistler dumps energetic (30-300 keV) electrons into the D region. The resulting ionization then alters the properties of the earthionosphere wave guide. The mechanism of precipitation is thought to be pitch angle scattering of trapped electrons that resonate with the magnetic field of the whistler wave near the magnetic equator. (auth)
253 citations
TL;DR: In this paper, it was shown that ELF hiss is present in the inner radiation zone (L less 2) during both storms and substorms, which is attributed to propagation of waves into this region from a distributed source located at high altitude near the equatorial plasmapause.
Abstract: It is shown that ELF hiss is present in the inner radiation zone (L less than 2) during both storms and substorms. This presence is ascribed to propagation of waves into this region from a distributed source located at high altitude near the equatorial plasmapause. Two major effects allow hiss to reach the inner zone during storms and substorms: (1) the observed tendency for plasmaspheric hiss to be greatly intensified during the recovery phase as the outward-moving plasmapause encounters the electrons that have been freshly injected into the magnetosphere; (2) the displacement of the plasmapause, and the presumed source region, to low altitudes during high levels of magnetic activity.
108 citations
01 Feb 1975
TL;DR: In this paper, the authors used pitch angle diffusion into the loss cone driven by the cyclotron resonant interaction to estimate the lifetime of inner-zone electrons, which ranges between 10 and 60 days.
Abstract: Broad band incoherent electromagnetic waves, called hiss, have been detected in the inner zone magnetosphere (L 10−6 γ²/Hz at the start of storm recovery phases, 10−7 – 10−6 γ²/Hz during substorms, and 0.4 to >3.1 MeV from L = 2 to L = 1.1, respectively. Characteristic lifetimes of inner zone electrons, calculated in order of magnitude fashion on the basis of pitch angle diffusion into the loss cone driven by the cyclotron resonant interaction, are found to range between 10 and 60 days. These computed lifetimes are consistent with observations of enhanced electron precipitation for L > 1.25 during storms. Although Coulomb scattering appears to be the dominant loss mechanism for L < 1.25, pitch angles scattering by the hiss may make a significant contribution to electron losses, especially during magnetically active intervals. The source of inner zone hiss has also been investigated. Two possible mechanisms of locally generating hiss in the inner zone, an electron cyclotron instability and a Landau resonance, are studied but are found to be unlikely candidates to give rise to hiss. Most features of inner zone hiss can be explained by the hypothesis that hiss originates in the vicinity of the plasmapause as plasmaspheric hiss, which is then able to propagate into the inner zone. There are two major effects that will allow this to occur during storms and substorms. The first is the intensification of plasmaspheric hiss as the freshly injected electrons convect and drift across the plasmapause into the high-density plasmasphere, leading to cyclotron instability. The second is the displacement of the plasmapause, and the presumed source region, to low L values during strong magnetic activity. This reduces the length of the ray paths leading to the inner zone and hence the amount of Landau damping. The present observations are compared with this propagation model and the two are found to be in good agreement.
95 citations
TL;DR: In this article, the effects of nighttime D region disturbances on long-distance subionospheric VLF propagation were investigated and it was shown that the energetic electrons that precipitate in the D region and cause the phase advances interacted with the whistler on its second hop.
Abstract: Observations of very rapid phase advances of up to 8° for subionospheric VLF transmissions over a path length of 5745 km are found to be associated with whistlers. We show that the energetic electrons that precipitate in the D region and cause the phase advances interacted with the whistler on its second hop, which is consistent with amplification of whistlers by cyclotron resonance with electrons traveling in the opposite direction. No fast amplitude variations were detected. We propose a simple two-mode model to describe the effects of nighttime D region disturbances on long-distance subionospheric VLF propagation, and we show how this model can account for our observations and also the amplitude effects seen by Helliwell, Katsufrakis, and Trimpi.
69 citations
TL;DR: In this article, the authors considered the effect of trapped particle flux at the edge of the loss cone on the expected occurrence characteristics of lightning-induced electron precipitation (LEP) events at longitudes of the western (110° W) versus eastern (71°W) United States.
Abstract: Expected occurrence characteristics of lightning-induced electron precipitation (LEP) events at longitudes of the western (110° W) versus eastern (71° W) United States are considered from the point of view of available trapped particle flux at the edge of the loss cone. Considering published data on nighttime fluxes of >68 keV electrons observed at L ≃ 2.5, and for “direct” precipitation into the northern hemisphere induced by northern hemisphere lightning, the occurrence rate and flux levels are expected to be a factor of 20–200 higher in the west than in the east, assuming no significant variation in lightning source activity with longitude. Again assuming lightning sources in the north, it is predicted that at 71° W, “mirrored” precipitation into the southern hemisphere would involve precipitation fluxes 30–300 times higher than “direct” precipitation into the northern hemisphere. However, at 110° W and again assuming lightning in the north, southern hemisphere precipitation would tend to be limited to that small fraction of particles that were initially scattered into the northern loss cone and that were then backscattered from the northern atmosphere so as to reach the south. Preliminary experimental investigation of these predictions is based on observations of lightning-associated perturbations of two geographically separate subionospheric VLF/LF signal paths, one (48.5 kHz) originating at Silver Creek, Nebraska, and observed at Stanford, California, and the other (28.5 kHz) originating at Aguadilla, Peurto Rico, and observed at Lake Mistissini, Quebec. The association of the characteristic VLF signal perturbations with lightning is generally evidenced by simultaneous (within ∼1 s) observation of single or multiple radio atmospherics. In most cases, high-resolution measurements of event signatures reveal a ∼0.5–1 s delay between the atmospheric and event onset, as well as an ∼1-s onset duration, consistent with theoretical predictions of a test particle model of the gyroresonant whistler-particle interaction. The data, considered in the light of previous observations in the southern hemisphere, provide qualitative support for several of the predictions based on considerations of the trapped flux level near the loss cone, in particular the prediction of comparable rates in the north at 110° W and the south at 71° W, and the prediction of substantially larger rates in the south than in the north near 71° W.
42 citations
"Phase and amplitude perturbations o..." refers background in this paper
...To explain Trimpi events one more mechanism is proposed by Inan et al. (1988): “early” Trimpi....
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...One such mechanism under discussion is the ‘early’ or ‘fast’ Trimpi (terminology introduced by Inan et al., 1988. bhu1-9-2010 Further many workers have shown that wave-particle interaction occurring in the equatorial plane near (L=1.09) can diffuse the pitch angle of the resonant electrons of…...
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