Coordinated Study of Coherent Radar Backscatter and Optical Airglow Depletions in the Central Pacific

Abstract

Equatorial plasma depletions have well-known seasonality and solar-cycle behavior. Except for a few well-instrumented sectors, much of these data have come from satellite sounding and in situ observations. We present a climatology of optical airglow images and 50 MHz coherent backscatter from the Pacific sector from solar maximum (January 2002) to solar minimum (January 2009). In contrast to in situ observations, we find that depletion activity remains quite high into solar minimum. However, the depletions and associated backscatter appear later in the evening and backscatter persists longer at solar minimum. Furthermore, we present individual nights that illustrate the day-to-day variability of depletion formation and their relationship to coherent backscatter echoes. The echoes originate from the depleted regions early in the evening but disappear as the night progresses.