Biblio

Found 7 results
Filters: Author is Glauert, Sarah A.  [Clear All Filters]
2018
Authors: Allison Hayley J., Horne Richard B, Glauert Sarah A, and Del Zanna Giulio
Title: Determination of the Equatorial Electron Differential Flux From Observations at Low Earth Orbit
Abstract: Variations in the high‐energy relativistic electron flux of the radiation belts depend on transport, acceleration, and loss processes, and importantly on the lower‐energy seed population. However, data on the seed population is limited to a few satellite missions. Here we present a new method that utilizes data from the Medium Energy Proton/Electron Detector on board the low‐altitude Polar Operational Environmental Satellites to retrieve the seed population at a pitch angle of 90°. The integral flux values measured by Medium Energy Proton/Electron Detector relate to a low equatorial pitch angle and were converted to omnidirectional flux using parameters obtained from fitting one or two urn:x-wiley:jgra:media:jgra54628:jgra54628-math-0001 functions to pitch angle distributions given . . .
Date: 11/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025786 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025786
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2014
Authors: Kersten Tobias, Horne Richard B, Glauert Sarah A, Meredith Nigel P, Fraser Brian J., et al.
Title: Electron losses from the radiation belts caused by EMIC waves
Abstract: Electromagnetic Ion Cyclotron (EMIC) waves cause electron loss in the radiation belts by resonating with high-energy electrons at energies greater than about 500 keV. However, their effectiveness has not been fully quantified. Here we determine the effectiveness of EMIC waves by using wave data from the fluxgate magnetometer on CRRES to calculate bounce-averaged pitch angle and energy diffusion rates for L*=3.5–7 for five levels of Kp between 12 and 18 MLT. To determine the electron loss, EMIC diffusion rates were included in the British Antarctic Survey Radiation Belt Model together with whistler mode chorus, plasmaspheric hiss, and radial diffusion. By simulating a 100 day period in 1990, we show that EMIC waves caused a significant reduction in the electron flux for energies greater t. . .
Date: 11/2014 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020366 Available at: http://doi.wiley.com/10.1002/2014JA020366
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Authors: Glauert Sarah A, Horne Richard B, and Meredith Nigel P
Title: Simulating the Earth's radiation belts: Internal acceleration and continuous losses to the magnetopause
Abstract: In the Earth's radiation belts the flux of relativistic electrons is highly variable, sometimes changing by orders of magnitude within a few hours. Since energetic electrons can damage satellites it is important to understand the processes driving these changes and, ultimately, to develop forecasts of the energetic electron population. One approach is to use three-dimensional diffusion models, based on a Fokker-Planck equation. Here we describe a model where the phase-space density is set to zero at the outer L∗ boundary, simulating losses to the magnetopause, using recently published chorus diffusion coefficients for 1.5≤L∗≤10. The value of the phase-space density on the minimum-energy boundary is determined from a recently published, solar wind-dependent, statistical model. Our s. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 7444 - 7463 DOI: 10.1002/jgra.v119.910.1002/2014JA020092 Available at: http://doi.wiley.com/10.1002/jgra.v119.9http://doi.wiley.com/10.1002/2014JA020092
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Authors: Zheng Liheng, Chan Anthony A, Albert Jay M, Elkington Scot R, Koller Josef, et al.
Title: Three-dimensional stochastic modeling of radiation belts in adiabatic invariant coordinates
Abstract: A 3-D model for solving the radiation belt diffusion equation in adiabatic invariant coordinates has been developed and tested. The model, named Radbelt Electron Model, obtains a probabilistic solution by solving a set of Itô stochastic differential equations that are mathematically equivalent to the diffusion equation. This method is capable of solving diffusion equations with a full 3-D diffusion tensor, including the radial-local cross diffusion components. The correct form of the boundary condition at equatorial pitch angle α0=90° is also derived. The model is applied to a simulation of the October 2002 storm event. At α0 near 90°, our results are quantitatively consistent with GPS observations of phase space density (PSD) increases, suggesting dominance of radial diffusion; at sm. . .
Date: 09/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 7615 - 7635 DOI: 10.1002/jgra.v119.910.1002/2014JA020127 Available at: http://doi.wiley.com/10.1002/jgra.v119.9http://doi.wiley.com/10.1002/2014JA020127
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2007
Authors: Meredith Nigel P, Horne Richard B, Glauert Sarah A, and Anderson Roger R
Title: Slot region electron loss timescales due to plasmaspheric hiss and lightning-generated whistlers
Abstract: [1] Energetic electrons (E > 100 keV) in the Earth's radiation belts undergo Doppler-shifted cyclotron resonant interactions with a variety of whistler mode waves leading to pitch angle scattering and subsequent loss to the atmosphere. In this study we assess the relative importance of plasmaspheric hiss and lightning-generated whistlers in the slot region and beyond. Electron loss timescales are determined using the Pitch Angle and energy Diffusion of Ions and Electrons (PADIE) code with global models of the spectral distributions of the wave power based on CRRES observations. Our results show that plasmaspheric hiss propagating at small and intermediate wave normal angles is a significant scattering agent in the slot region and beyond. In contrast, plasmaspheric hiss propagating at large. . .
Date: 08/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2007JA012413 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2007JA012413/abstract
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2006
Authors: Meredith Nigel P, Horne Richard B, Glauert Sarah A, Thorne Richard M, Summers D., et al.
Title: Energetic outer zone electron loss timescales during low geomagnetic activity
Abstract: Following enhanced magnetic activity the fluxes of energetic electrons in the Earth's outer radiation belt gradually decay to quiet-time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 ≤ L ≤ 5.0 occurs during quiet periods (Kp < 3−) following enhanced magnetic activity on timescales ranging from 1.5 to 3.5 days for 214 keV electrons to 5.5 to 6.5 days for 1.09 MeV electrons. The intervals of decay are associated with large average values of the ratio fpe/fce (>7), indicating that the decay takes place in the plasmasphere. We compute loss timescales for pitch-angle scattering by plasmaspheric hiss using the PADIE code with wave properties based on C. . .
Date: 05/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011516 Available at: http://onlinelibrary.wiley.com/doi/10.1029/2005JA011516/abstract
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2005
Authors: Horne Richard B, Thorne Richard M, Shprits Yuri Y, Meredith Nigel P, Glauert Sarah A, et al.
Title: Wave acceleration of electrons in the Van Allen radiation belts
Abstract: The Van Allen radiation belts1 are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar activity2, 3 and they represent a hazard to satellites and humans in space4, 5. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth6, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase . . .
Date: 09/2005 Publisher: Nature Pages: 227 - 230 DOI: 10.1038/nature03939 Available at: http://www.nature.com/nature/journal/v437/n7056/full/nature03939.html
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