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

Abstract

[1] 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.

On the origin of mesoscale TIDs at midlatitudes

“…Each image has been standardized so that north is at the top and east is to the right (after Kelley et al, 2002, reproduced with permission of Elsevier). Haldoupis et al (2003) and Kelley et al (2003) showed experimentally that the E-and F-regions are closely coupled in this process. Theoretical work has lagged far behind experiments.…”

<i>E</i>-region wind-driven electrical coupling of patchy sporadic-<i>E</i> and spread-<i>F</i> at midlatitude

“…As discussed in the papers by Kelley et al (2003) and Haldoupis et al (2003), an eastward polarization electric field of 5 mV/m inside a medium-scale E s patch will map instantly up along the field lines to produce a 50-km uplift of the F region bottomside in about 10 min, whereas a 10-mV/m field will need only about 5 min for the same uplift. This process will be much more effective if both the sporadic-E patch below and the uplifted plasma region above are somehow kept "in contact", by moving horizontally with comparable velocities.…”

“…On the other hand, Swartz et al (2002) estimated the F to E region conductance ratio to be near 5 or greater during normal conditions but drops to almost 1.5 during times when a strongly uplifted F layer above and an intense sporadic-E layer below occurred concurrently. Also, in the two spread-F events studied by Kelley et al (2003), the ratio of F to E-layer height integrated Pedersen conductivities was estimated to be in the range from 1.5 to 10. Given all this, we take 1<Z<10.…”

“…Recently, two companion papers by Kelley et al (2003) and Haldoupis et al (2003) provided supporting evidence and proposed a new mechanism on the role of patchy sporadic-E layers in forming medium scale spread-F at midlatitude. In this mechanism, enhanced electric fields inside sporadic-E patches can map along the magnetic field lines up to the F region, to uplift the plasma and generate spread-F .…”

“…For completeness, we describe here, in brief, the mechanism for intermediate scale spread-F generation at midlatitude, proposed recently by Kelley et al (2003) and . The process is outlined in Fig.…”