Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements

Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest tha...

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Bibliographic Details
Published in:	Journal of Geophysical Research Vol. 117; no. A12; pp. A12203 - n/a
Main Authors:	Forsyth, C., Fazakerley, A. N., Walsh, A. P., Watt, C. E. J., Garza, K. J., Owen, C. J., Constantinescu, D., Dandouras, I., Fornaçon, K.-H., Lucek, E., Marklund, G. T., Sadeghi, S. S., Khotyaintsev, Y., Masson, A., Doss, N.
Format:	Journal Article
Language:	English
Published:	Washington, DC Blackwell Publishing Ltd 01-12-2012 American Geophysical Union
Subjects:	Altitude Atmospheric sciences auroral acceleration Current Systems Earth, ocean, space Electric fields Electric potential electric potentials Electrostatic Shocks Exact sciences and technology External geophysics Field-Aligned Currents High-Altitude Interaction between magnetosphere and interplanetary space Ion-Beams Magnetic-Field Magnetism multispacecraft Omega-Bands Particle-Acceleration Physics of the magnetosphere Plasma physics Plasma Sheet Poynting Flux Space Spacecraft CLUSTER satellite Offence (violation) models Electric potential Aurorae Satellite observation Particle acceleration Invariance Current density Double electrostatic layer Electrostatic potential
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Summary:	Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multispacecraft observations from Cluster, we have examined two upward current regions on 14 December 2009. Our observations show that the potential difference below C4 and C3 changed by up to 1.7 kV between their respective crossings, which were separated by 150 s. The field‐aligned current density observed by C3 was also larger than that observed by C4. The potential drop above C3 and C4 was approximately the same in both crossings. Using a novel technique of quantitively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made effectively magnetically conjugate observations, and we use these conjugate observations to determine the instantaneous distribution of the potential drop in the AAR. Our observations show that an average of 15% of the potential drop in the AAR was located between C1 at 6235 km and C3 at 4685 km altitude, with a maximum potential drop between the spacecraft of 500 V, and that the majority of the potential drop was below C3. Assuming a spatial invariance along the length of the upward current region, we discuss these observations in terms of temporal changes and the vertical structure of the electrostatic potential drop and in the context of existing models and previous single‐ and multispacecraft observations. Key Points First conjugate and temporal observations of AAR by Cluster 15% of potential drop between spacecraft inside AAR Potential drop increases at lower altitudes, constant at high altitudes
Bibliography:	istex:526AB85AAEF61C6E21400793F7AAA47D63C04AD9 ArticleID:2012JA017655 Tab-delimited Table 1. ark:/67375/WNG-78LXZHJV-J
ISSN:	0148-0227 2169-9380 2156-2202 2156-2202 2169-9402
DOI:	10.1029/2012JA017655