Auroral electrodynamics from simultaneous measurements at high and low altitudes

Two 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.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Natural Sciences

Grantor

Rice University

Year dc:date.issued

1991

Author dc:creator

• Lu, Gang

Advisor dc:contributor.advisor

• Reiff, Patricia H.

• Astronomy
• Astrophysics

Statement dc:rights

• Copyright 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.

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1911/19078

OAI identifier oai:identifier

oai:repository.rice.edu:1911/19078