Centrifugal acceleration of the polar wind
Journal Article
·
· Journal of Geophysical Research
- Univ. of Alabama, Huntsville, AL (United States); and others
The effect of parallel ion acceleration associated with convection was first applied to energization of test particle polar ions by Cladis. However, this effect is typically neglected in {open_quotes}self-consistent{close_quotes} models of polar plasma outflow, apart from the fluid simulation by Swift. The authors include approximations for this acceleration, which they broadly characterize as centrifugal in nature, in their time-dependent, semikinetic model of polar plasma outflow. The authors find that the steady state O{sup +} bulk velocities and parallel temperatures strongly increase and decrease, respectively, with convection strength. In particular, the bulk velocities increase from near 0 km s{sup {minus}1} at 4000 km altitude to {approximately} 10 km s{sup {minus}1} at 5 R{sub E} geocentric distance for a 50-mV/m ionospheric convection electric field. However, the centrifugal effect on the steady O{sup +} density profiles depends on the exobase ion and electron temperatures: for low-base temperatures (T{sub i} = T{sub e} = 3000 K) the O{sup +} density at high altitudes increases greatly with convection, while for higher base temperatures (T{sub i} = 5000 K, T{sub e} = 9000 K), the high-altitude O{sup +} density decreases somewhat as convection is enhanced. The centrifugal force further has a pronounced effect on the escaping O{sup +} flux, especially for cool exobase conditions; as referenced to the 4000-km altitude, the steady state O{sup +} flux increases from 10{sup 5} ions cm{sup {minus}2} s{sup {minus}1} when the ionospheric convection field E{sub i} = 0 mV/m to {approximately} 10{sup 7} ions cm{sup {minus}2} s{sup {minus}1} when E{sub i} = 100 mV/m. The centrifugal acceleration described is a possible explanation for the large (up to {approximately} 10 km s{sup {minus}1} or more) O{sup +} outflow velocities observed in the midlatitude polar magnetosphere with the Dynamics Explorer 1 and Akebono spacecraft. 37 refs.
- OSTI ID:
- 102617
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A8 Vol. 99; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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