Transequatorial Propagation and Depletion Precursors

Monday, 15 December 2014: 5:15 PM
Ethan S Miller, JHU/APL, Laurel, MD, United States, Gary S Bust, JHU Applied Physics Lab, Laurel, MD, United States, Stephen Roland Kaeppler, SRI International, Menlo Park, CA, United States, Nathaniel A Frissell, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States and Larry J Paxton, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States
The bottomside equatorial ionosphere in the afternoon and evening sector frequently evolves rapidly from smoothly stratified to violently unstable with large wedges of depleted plasma growing through to the topside on timescales of a few tens of minutes. These depletions have numerous practical impacts on radio propagation, including amplitude scintillation, field-aligned irregularity scatter, HF blackouts, and long-distance transequatorial propagation at frequencies above the MUF. Practical impacts notwithstanding, the pathways and conditions under which depletions form remain a topic of vigorous inquiry some 80 years after their first report. Structuring of the pre-sunset ionosphere---morphology of the equatorial anomalies and long-wavelength undulations of the isodensity contours on the bottomside---are likely to hold some clues to conditions that are conducive to depletion formation. The Conjugate Depletion Experiment is an upcoming transequatorial forward-scatter HF/VHF experiment to investigate pre-sunset undulations and their connection with depletion formation. We will present initial results from the Conjugate Depletion Experiment, as well as a companion analysis of a massive HF propagation data set.