Auroral electrodynamics from simultaneous measurements at high and low altitudes

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dc.contributor.advisorReiff, Patricia H.en_US
dc.creatorLu, Gangen_US
dc.date.accessioned2009-06-04T08:49:40Zen_US
dc.date.available2009-06-04T08:49:40Zen_US
dc.date.issued1991en_US
dc.description.abstractTwo auroras sampled nearly simultaneously at high and low altitudes along a field line by the Dynamics Explorer (DE) spacecraft have been used to study auroral electrodynamics. Electric fields plotted as a function of invariant latitude show that the large-scale features are essentially the same at high and low altitudes outside the auroral acceleration region. Parallel electric fields associated with parallel currents are such as to filter out the small-scale structure in the high-altitude electric field pattern. From the magnetic field measurements, we find that there is a return current region embedded between two auroral arc structures. The latitude shift between the high-altitude and low-altitude return current regions indicates that the auroral arcs are moving equatorward with a velocity of about 250 m/s. Collisionless plasma kinetic theory (Knight, 1973) has been used to predict the relationship between the upward parallel current and the parallel potential drop. The DE 1/DE 2 pair offers a unique Opportunity to test this relationship because the DE 1 spacecraft can measure high altitude plasma parameters without contamination from auroral heating. Using measured values of J$\sb{\Vert}$ (mapped to the surface) and $\Phi\sb{\Vert}$, the ratio of J$\sb{\Vert}$/e$\Phi\sb{\Vert}$ varies considerably but with a mean value about 0.5$\sim$2.2 $\times$ 10$\sp{-9}$ mho/m$\sp2$. Suprathermal electron bursts are also observed in the diffuse aurora at the same invariant latitudes, both at high and at low altitudes. Thus we suggest that these "bursts" are more properly described as a spatial rather than temporal phenomenon. Observations of upflowing ionospheric ions are obtained by both DE 1 and DE 2 over the nightside auroral regions. At low altitudes, the mean value of the net upward ion number flux is of the order of 10$\sp9$ cm$\sp{-2}$ s$\sp{-1}$. The ionosphere is predominantly O$\sp+$, and the ions with energies greater than 5 eV are a only very small fraction (less than 1%) of the total ion population. At high altitudes, the upflowing ions are accelerated and heated (with characteristic energies of hundreds of eV). Comparing upflowing fluxes at high and low altitudes yields an estimated height of the bottom of the auroral acceleration region of 1100-1400 km.en_US
dc.format.extent127 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoThesis Sp. Sci. 1991 Luen_US
dc.identifier.citationLu, Gang. "Auroral electrodynamics from simultaneous measurements at high and low altitudes." (1991) Diss., Rice University. <a href="https://hdl.handle.net/1911/19078">https://hdl.handle.net/1911/19078</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/19078en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectAstronomyen_US
dc.subjectAstrophysicsen_US
dc.titleAuroral electrodynamics from simultaneous measurements at high and low altitudesen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentSpace Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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