Radio and optical techniques for locating equatorial plasma irregularities

Plasma density depletions occur in the post-sunset F region ionosphere almost nightly during certain seasons at equatorial latitudes. These depletions contain density irregularities of scales ranging from a few centimeters to thousands of kilometers. Spread-F, the disruption of ionospheric measurements with ionosondes and incoherent scatter radar, and scintillation (fading) of trans-ionospheric radio communication and navigation signals are well-known symptoms of depletions. This dissertation describes new techniques to combine optical and radio ionospheric remote sensing data in common formats to leverage observational strengths and mitigate weaknesses, leading to new or improved physical interpretations. Principally, a technique for locating scintillation-causing irregularities in the Earth's equatorial regions using radio occultation and airglow imaging is presented. A similar technique is employed to study the relationship between Bragg-scale radar backscatter and depletions observed with the airglow imager. A climatology of airglow and radar data from the central Pacific that uncovers regularly occurring post-midnight depletions is also presented. Combined airglow and radar data from these events suggest that polarization electric fields within mesoscale traveling ionospheric disturbances (MSTIDs) seed post-midnight equatorial plasma depletions during geomagnetic quiet periods at solar minimum.