North‐south aligned equatorial airglow depletions

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Abstract
A new instrument for all‐sky spectrophotometric imaging of aurora and airglow has been installed in the Air Force Geophysics Laboratory's Airborne ionospheric Observatory. Initial observations of equatorial and near‐equatorial 6300‐Å O I airglow show the existence of north‐south aligned regions of airglow depletion. These dark bands often extend more than 1200 km in the north‐south direction and 50–200 km in the east‐west direction. They are observed to drift toward the east during the evening‐midnight hours, with one observation of westward drift after local midnight. Airglow fine structure associated with the boundaries of the dark bands has been observed down to the 2.5‐km resolution limit of the instrument. Simultaneous airborne ionospheric soundings indicate that these regions of airglow depletion are characterized by an increase in the virtual height of the F layer. A simple model of field‐aligned electron density depletion in the bottomside of the F layer explains both the airglow observations and the ionospheric soundings.

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