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On the High- and Low- Altitude Limits of the Auroral Electric Field RegionUsing measurements from the High Altitude Plasma Instrument (HAPI) on the Dynamics-Explorer 1 (DE-1) spacecraft and the Low Altitude Plasma Instrument (LAPI) on Dynamics Explorer 2 (DE 2), we investigate both die high altitude and low altitude extents of the auroral acceleration region. To infer the high altitude limit, we searched the HAPI data base for evidence of upward-directed auroral electric fields located above the spacecraft when the HAPI spacecraft is above 9000 km altitude. We find that such acceleration is common when DE-1 flies through die auroral oval at an altitude of 9,000-11,000 km. At altitudes above 11,000 km, the fraction of the orbits with evidence of at least a 1000 V potential drop above the spacecraft falls, becoming essentially zero above an altitude of 15,000 km. Above that altitude, small (100 V) potential drops are frequently observed, but only rarely are approx. 1 kV potentials observed, typically associated with polar cap or 'theta' arcs or westward traveling surges. To investigate the low-altitude limit of the auroral acceleration region, we use conjunctions of DE 1 and DE 2 along auroral field lines and match the upgoing fluxes of ionospheric ions observed by DE 2 with the flux of accelerated upgoing ions observed at DE 1. Calculating the ionospheric scale height from the ion and electron temperatures and assuming that the parallel flow velocity is independent of height above 800 km, we calculate the altitude at which the upwelling ionospheric ions are effectively completely lost to upward acceleration. The initial lowest-altitude acceleration process could be either a perpendicular acceleration or a parallel electric field, but it must be sufficient to give the entire distribution escape energy. We find that in the two cases studied, near the region of peak auroral potential drop the altitude of this acceleration was around 1700 km (near the O/H neutral crossover altitude), but was significantly higher (approx. 2000 km) near the edges of the arc, where the potential was lower. The composition of the upgoing ion beam was consistent with these heights, being predominately H(+) near the edges and O(+) near the peak.
Document ID
19970031416
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Reiff, P. H.
(Rice Univ. Houston, TX United States)
Lu, G.
(National Center for Atmospheric Research Boulder, CO United States)
Burch, J. L.
(Southwest Research Inst. San Antonio, TX United States)
Winningham, J. D.
(Southwest Research Inst. San Antonio, TX United States)
Frank, L. A.
(Iowa Univ. Iowa City, IA United States)
Craven, J. D.
(Alaska Univ. Fairbanks, AK United States)
Peterson, W. K.
(Lockheed Missiles and Space Co. Palo Alto, CA United States)
Heelis, R. A.
(Texas Univ. at Dallas Richardson, TX United States)
Date Acquired
August 17, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Auroral Plasma Dynamics
Publisher: American Geophysical Union
Subject Category
Geophysics
Report/Patent Number
NASA-CR-204419
NAS 1.26:204419
Accession Number
97N72373
Funding Number(s)
CONTRACT_GRANT: NSF ATM-91-03440
CONTRACT_GRANT: NAGw-2735
CONTRACT_GRANT: NAG5-483
CONTRACT_GRANT: NAG5-775
CONTRACT_GRANT: NAS5-33030
CONTRACT_GRANT: NAS5-33032
CONTRACT_GRANT: NAGw-1655
CONTRACT_GRANT: NAG5-1915
Distribution Limits
Public
Copyright
Public Use Permitted.
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