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Seeding of equatorial plasma depletions by polarization electric fields from middle latitudes: Experimental evidence
Author(s) -
Miller E. S.,
Makela J. J.,
Kelley M. C.
Publication year - 2009
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 - 10.1029/2009gl039695
Subject(s) - ionosphere , geophysics , instability , earth's magnetic field , geology , middle latitudes , sunset , f region , electric field , atmospheric sciences , airglow , substorm , plasma , equator , latitude , magnetic field , physics , magnetosphere , geodesy , astronomy , quantum mechanics , mechanics
It is well‐known that large wedges of depleted plasma often form in the equatorial ionosphere after sunset. Irregularities in and around these depletions cause scintillation on trans‐ionospheric radio paths, as well as strong VHF backscatter. The ultimate stage of depletion growth is controlled by a collisional interchange instability. However, the initiation stages remain the subject of debate. Depletions formed in the first 1–3 hours after sunset are probably seeded by instability processes operating in the valley region from 150–250 km. However, depletions that form later in the evening do not benefit from the rapid pre‐reversal enhancement of the zonal electric field nor the sheared flow of the evening vortex. We investigate evidence from airglow images and VHF coherent backscatter that a polarization electric field associated with an ionospheric instability process at middle latitudes may induce the formation of post‐midnight depletions at the geomagnetic equator during geomagnetically‐quiet periods.