Case studies of coupling between the E and F regions during unstable sporadic‐E conditions

Simultaneous F ‐region airglow, E ‐region coherent‐scatter radar, and ionosonde observations were made in Greece during the summer sporadic‐ E season in 2002. In this paper we report on two case studies during which patchy sporadic‐ E layers were accompanied by midlatitude spread F , coherent VHF radar echoes (including two‐stream echoes), and traveling ionospheric disturbances registered by the airglow instrument. We argue that these events give strong evidence that polarization electric fields are built up in the E region and are mapped upward to the F region, creating rising and falling regions in the bottomside plasma. The resulting structure creates conditions for midlatitude spread F , as detected by the ionosonde. This correlation between patchy sporadic E and midlatitude spread F is further supported in a companion paper. Upward coupling of this sort is particularly efficient in regions of F ‐region plasma uplift and airglow depletion, since the F ‐region Pedersen conductivity is low which reduces the electrical load on the E ‐region generator.