Bibliography

Electron precipitation models in global magnetosphere simulations

General methods for improving the specification of electron precipitation in global simulations are described and implemented in the Lyon-Fedder-Mobarry (LFM) global simulation model, and the quality of its predictions for precipitation is assessed. LFM\textquoterights existing diffuse and monoenergetic electron precipitation models are improved, and new models are developed for lower energy, broadband, and direct-entry cusp precipitation. The LFM simulation results for combined diffuse plus monoenergetic electron precipitation exhibit a quadratic increase in the hemispheric precipitation power as the intensity of solar wind driving increases, in contrast with the prediction from the OVATION Prime (OP) 2010 empirical precipitation model which increases linearly with driving intensity. Broadband precipitation power increases approximately linearly with driving intensity in both models. Comparisons of LFM and OP predictions with estimates of precipitating power derived from inversions of Polar satellite UVI images during a double substorm event (28\textendash29 March 1998) show that the LFM peak precipitating power is \>4\texttimes larger when using the improved precipitation model and most closely tracks the larger of three different inversion estimates. The OP prediction most closely tracks the double peaks in the intermediate inversion estimate, but it overestimates the precipitating power between the two substorms by a factor \>2 relative to all other estimates. LFMs polar pattern of precipitating energy flux tracks that of OP for broadband precipitation exhibits good correlation with duskside region 1 currents for monoenergetic energy flux that OP misses and fails to produce sufficient diffuse precipitation power in the prenoon quadrant that is present in OP. The prenoon deficiency is most likely due to the absence of drift kinetic physics in the LFM simulation.

Zhang, B.; Lotko, W.; Brambles, O.; Wiltberger, M.; Lyon, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2015

YEAR: 2015     DOI: 10.1002/2014JA020615

electron precipitation; global magnetosphere simulation; magnetosphere-ionosphere coupling

Statistical relationship between large-scale upward field-aligned currents and electron precipitation

Simultaneous observations of Birkeland currents by the constellation of Iridium satellites and N2 Lyman\textendashBirge\textendashHopfield (LBH) auroral emissions measured by the Global Ultraviolet Imager (GUVI) onboard the Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) satellite are used to establish relationships between large-scale upward field-aligned currents and electron precipitation during stable current configurations. The electron precipitation was inferred from GUVI data using a statistical relationship between LBH intensity and electron energy flux. LBH emissions with \>5\% contribution from protons, identified by Lyman-alpha intensity, were excluded from the analysis. The Birkeland currents were derived with a spatial resolution of 3\textdegree in latitude and 2 h in local time. For southward interplanetary magnetic field (IMF), the electron precipitation occurred primarily within and near large-scale upward currents. The correspondence was less evident for northward IMF, presumably because the spatial variability is large compared to the areas of interest so that the number of events identified is smaller and the derived statistical distributions are less reliable. At dusk, the correlation between upward current and precipitation was especially high, where a larger fraction of the electron precipitation is accelerated downward by a field-aligned potential difference. Unaccelerated electron precipitation dominated in the morning sector, presumably induced by scattering of eastward-drifting energetic electrons into the loss cone through interaction with whistler-mode waves (diffuse precipitation) rather than by field-aligned acceleration. In the upward Region 1 on the dayside, where electron precipitation is almost exclusively due to field-aligned acceleration, a quadratic relationship between current density and electron energy flux was observed, implying a linear current\textendashvoltage relationship in this region. Current density and electron energy flux in the regions of the large-scale upward currents from pre-midnight through dawn to noon are essentially uncorrelated consistent with a dominance of diffuse electron precipitation to the incident energy flux.

Korth, Haje; Zhang, Yongliang; Anderson, Brian; Sotirelis, Thomas; Waters, Colin;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2014     DOI: 10.1002/2014JA019961

Birkeland Currents; Auroral Emissions; electron precipitation; Current-Precipitation Relationship; Current-Voltage Relationship

Empirical relationship between electron precipitation and far-ultraviolet auroral emissions from DMSP observations

Auroral emissions observed in the far-ultraviolet wavelength range are compared with measurements of the coincident precipitating electrons and ions that produce the emissions in a large-scale correlative study. The auroral emissions and particle precipitation are observed with the Special Sensor Ultraviolet Spectrographic Imager and SSJ5 detectors, respectively, both onboard the DMSP F16 satellite. Coincident observations along the same magnetic field line in the Northern Hemisphere are assembled from two consecutive winters (during 2005\textendash2007). A numerical fit to 27,922 coincident observations provides an empirical relationship between the electron energy flux and the intensity of Lyman-Birge-Hopfield long emissions, J_Ee = 4.90 .10⁸ (eV s^\textendash1 sr^\textendash1 cm^\textendash2)/R I_LBHL (valid in the absence of significant ion fluxes: J_Ee \> 10 J_Eion). A fit to 1308 coincident observations provides the relationship between the average electron energy and the Lyman-Birge-Hopfield short to Lyman-Birge-Hopfield long emission ratio, \<E_e \> = 19.6 keV exp(\textendash2.34 I_LBHS / I_LBHL) (valid from 3 to 19.6 keV). These resulting empirical relationships permit the energy flux and average energy of precipitating electrons to be inferred from far-ultraviolet imagery, in the absence of significant ion precipitation.

Sotirelis, Thomas; Korth, Haje; Hsieh, Syau-Yun; Zhang, Yongliang; Morrison, Daniel; Paxton, Larry;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2013

YEAR: 2013     DOI: 10.1002/jgra.50157

DMSP; electron aurora; electron precipitation; FUV Aurora