Relationship of O+ field-aligned flows and densities to convection speed in the polar cap at 5000 km altitude

Autor: H. A. Elliott, Paul D. Craven, Thomas E. Moore, R. H. Comfort, B. Creel, J. L. Horwitz, B. A. Stevenson, Y.-J. Su
Rok vydání: 2000
Předmět:
Zdroj: Journal of Atmospheric and Solar-Terrestrial Physics. 62:495-503
ISSN: 1364-6826
DOI: 10.1016/s1364-6826(00)00030-4
Popis: Measurements of thermal O(+) ion number fluxes, densities, field-aligned velocities, and convective velocities from the Thermal Ion Dynamics Experiment (TIDE) on POLAR obtained near 5000 km altitude over the Southern hemisphere are examined. We find that the O(+) parallel velocities and densities are strongly related to the convection speeds. The polar cap densities decrease rapidly with convection speed, with a linear least square fit formula to bin averaged data giving the relationship log(N(sub (sub _)O(+))) = -0.33* V(sub (sub _)conv)) + 0.07, with a linear regression coefficient of r = -0.96. The parallel bulk flow velocities are on average slightly downward (0 - 2 km/s) for V(sub (sub _)conv) 2.5 km/s. We interpret these relationships in terms of the Cleft Ion Fountain paradigm [e.g., Horwitz and Lockwood, 1985]. The densities decline with convection speed owing to increased spreading and resulting dilution from the restricted cleft source over the polar cap area with convection speed. The parallel velocities tend to be downward for low convection speeds because they fall earthward after initial cleft injection at shorter distances into the polar cap for low convection speeds. At the higher convection speeds, the initially-upward flows are transported further into the polar cap and thus occupy a larger area of the polar cap.
Databáze: OpenAIRE
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