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Relationship of O(+) Field-Aligned Flows and Densities to Convection Speed in the Polar Cap at 5000 km AltitudeMeasurements 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, but tend to be upward (0 - 4 km/s) for average 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.
Document ID
19990116266
Acquisition Source
Marshall Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Stevenson, B. A.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Horwitz, J. L.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Creel, B.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Elliott, H. A.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Comfort, R. H.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Su, Y. J.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Moore, T. E.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Craven, P. D.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1999
Subject Category
Geophysics
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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