Images of bottomside irregularities observed at topside altitudes

Abstract

We analyzed plasma and field measurements acquired by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during an eight‐hour period on 13–14 January 2010 when strong to moderate 250 MHz scintillation activity was observed at nearby Scintillation Network Decision Aid (SCINDA) ground stations. C/NOFS consistently detected relatively small‐scale density and electric field irregularities embedded within large‐scale (∼100 km) structures at topside altitudes. Significant spectral power measured at the Fresnel (∼1 km) scale size suggests that C/NOFS was magnetically conjugate to bottomside irregularities similar to those directly responsible for the observed scintillations. Simultaneous ion drift and plasma density measurements indicate three distinct types of large‐scale irregularities: (1) upward moving depletions, (2) downward moving depletions, and (3) upward moving density enhancements. The first type has the characteristics of equatorial plasma bubbles; the second and third do not. The data suggest that both downward moving depletions and upward moving density enhancements and the embedded small‐scale irregularities may be regarded as Alfvénic images of bottomside irregularities. This interpretation is consistent with predictions of previously reported theoretical modeling and with satellite observations of upward‐directed Poynting flux in the low‐latitude ionosphere.