Photoelectron effects on the self-consistent potential in the collisionless polar wind

Details Photoelectron effects on the self-consistent potential in the collisionless polar wind Photoelectron effects on the self-consistent potential in the collisionless polar wind

Apr 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jgr...102.7509k&link_type=abstract

Journal of Geophysical Research, Volume 102, Issue A4, p. 7509-7522

Physics

Plasma Physics

21

Ionosphere: Electric Fields, Ionosphere: Polar Cap Ionosphere, Ionosphere: Solar Radiation And Cosmic Ray Effects, Space Plasma Physics: Transport Processes

Scientific paper

The presence of unthermalized photoelectrons in the sunlit polar cap leads to an enhanced ambipolar potential drop and enhanced upward ion acceleration. Observations in the topside ionosphere have led to the conclusion that large-scale electrostatic potential drops exist above the spacecraft along polar magnetic field lines connected to regions of photoelectron production. A kinetic approach is used for the O+, H+, and photoelectron (p) distributions, while a fluid approach is used to describe the thermal electrons (e) and self-consistent electric field (E∥). Thermal electrons are allowed to carry a flux that compensates for photoelectron escape, a critical assumption. Collisional processes are excluded, leading to easier escape of polar wind particles and therefore to the formation of the largest potential drop consistent with this general approach. We compute the steady state electric field enhancement and net potential drop expected in the polar wind due to the presence of photoelectrons as a function of the fractional photoelectron content and the thermal plasma characteristics. For a set of low-altitude boundary conditions typical of the polar wind ionosphere, including 0.1% photoelectron content, we found a potential drop from 500 km to 5RE of 6.5 V and a maximum thermal electron temperature of 8800 K. The reasonable agreement of our results with the observed polar wind suggests that the assumptions of this approach are valid.

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