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Seasonal variations along auroral field lines: Measurements from the Polar spacecraft
Author(s) -
Johnson M. T.,
Wygant J. R.,
Cattell C. A.,
Mozer F. S.
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2002gl015866
Subject(s) - ionosphere , electric field , physics , altitude (triangle) , polar , plasma , atmospheric sciences , amplitude , field line , geophysics , computational physics , environmental science , astronomy , optics , geometry , mathematics , quantum mechanics
Measurements from the Polar electric field instrument are used to study large electric fields and the ambient plasma density as a function of altitude (1.8–6.0 R E geocentric). Results from the premidnight sector (1800–2400 MLT) along auroral field lines show roughly a fourfold increase in the occurrence of small scale size, large amplitude electric fields (>100 mV m −1 ) at altitudes from 1.9 to 2.5 R E for dark compared to sunlit ionospheric conditions. Density values inferred from spacecraft potential measurements show these electric fields to be correlated with low plasma densities (0.2 to 3.0 cm −3 ). An increase in the average plasma density from 10 to 60 cm −3 is also observed for sunlit compared to dark conditions for the same altitude range. In addition, the distribution of density measurements from 1.9 to 2.2 R E also show evidence for an increase in cold ionospheric plasma (from ∼30 to 60 cm −3 ) for sunlit compared to dark ionospheric conditions.