Mesoscale structure of the midlatitude ionosphere during high geomagnetic activity: Airglow and GPS observations

On the night of November 22, 1997, the Cornell All-Sky Imager recorded a sp ectacular display of structure in the 630.0 nm emission over Arecibo, Puert o nice. This event is an example of a phenomenon we have termed "intense mi dlatitude spread F." In this paper we describe the stormtime geophysical co nditions for the period and detail the evolution of the event. The daytime midlatitude ionosphere was disturbed for four consecutive days. The initial daytime doubling of the total electron content (TEC) was associated with e quatorward propagation of a high-TEC patch that seemed to have associated c omposition changes. The following days had distinct diurnal double maxima ( DDM). The TEC in the Caribbean was very high during the first night of the storm and was extremely structured. Airglow depletions and enhancements sur ged poleward, bifurcating numerous times in the process. The airglow deplet ions were collocated wit;ll TEC minima along similar lines of sight to Glob al Positioning System satellites. Eventually, four parallel and very simila r airglow wave packets were visible and oriented at an angle similar to the less violent structures reported in the companion paper [Garcia et al., th is issue] and moving slowly toward the southwest. We explore a number of po ssible explanations for these features. We are most confident that secondar y instabilities of the generalized ExB process can explain the evolution of the structures once they are formed. The initial process itself remains co ntroversial.