Polar cap auroral arcs: Observations, theories, and a numerical model

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:121158

Berg, G A

This thesis reports the results of probably the most completely documented study of auroras near the polar cap boundary performed to date. Three fully instrumented rockets flew into the morning sector of the polar cap, complemented on the ground by a digital all-sky camera and incoherent scatter radar. Additionally, DMSP satellite passes over the polar cap bracketed the launches. We use these data to address two main issues: (1) the relationship between the state of the magnetosphere and the formation of polar cap arcs, and (2) the character of the current systems associated with polar cap arcs. The data indicate that in a decaying magnetosphere sun-aligned arcs erupt into the polar cap at high velocity from regions of enhanced brightness in the auroral oval. Two bright polar cap arcs formed in this manner in the region sampled by the rockets. The most equatorward of the arcs, sampled by two of the rockets during its lifetime, erupted into a region already characterized by strong sunward convection. The most poleward, however, which formed after the rockets had passed, pushed into a region where anti-sunward convection pertained less than two minutes earlier. It is likely that the boundary between sunward and anti-sunward convection shifted poleward so that sunward convection pertained at this arc as well. One of the payloads measured, with high resolution, both E and {delta}B as well as energetic particle flux. This permitted an in-depth study of the current systems flown through. The correlation between {delta}E and {delta}B is classic, both fields indicating upward field-aligned currents in virtually every region of enhanced electron precipitation. However, the currents deduced from the electrons do not agree in magnitude with those deduced from the fields. The conclusion is that for arcs embedded in a region of low {Sigma}{sub P} a current composed of upward thermal electrons flows concurrently with the precipitating electrons.

• Research Organization: Cornell Univ., Ithaca, NY (United States)
• OSTI ID: 121158
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
EARTH MAGNETOSPHERE
POLAR-CAP AURORAE