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Large‐scale auroral plasma density cavities observed by Freja
Author(s) -
Lundin R.,
Eliasson L.,
Haerendel G.,
Boehm M.,
Holback B.
Publication year - 1994
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 - 10.1029/94gl00888
Subject(s) - ionosphere , plasma , transverse plane , ion , physics , field line , geophysics , f region , satellite , plasma acceleration , orbit (dynamics) , atomic physics , astronomy , nuclear physics , structural engineering , quantum mechanics , aerospace engineering , engineering
Freja, the joint Swedish and German scientific satellite, has an orbit inclination that allows it to traverse the auroral oval tangentially and stay for minutes on field lines connected to the auroral energization region. One signature of the auroral energization process is the heating/transverse energization of ionospheric ions. Associated with such transverse heating/energization of ionospheric ions is a depletion of cold plasma in the topside ionosphere. We have studied several Freja passes at ≈1700 km altitude with long time periods of plasma depletion and transverse ion acceleration. Inside these depletion regions the density may decrease by more than two orders of magnitude (from 1000 to ≈10 cm −3 ). This suggests that transverse ion heating is indeed a very strong mechanism for plasma density depletion in the topside ionosphere.