Caribbean Ionosphere Campaign, Year One: Airglow and plasma observations during two intense mid-latitude spread-F events

A series of campaigns has been carried out in the Caribbean over a one-year period to study intense midlatitude spread-F events using a cluster of div ersified instrumentation. These events are relatively rare but a number of them have now been captured and will be discussed in this and several compa nion papers. This paper focuses on 630 nm airglow images obtained by the Co rnell All-Sky Imager for two of the more spectacular cases that began on Fe bruary 17, 1998 and February 17, 1999. In the latter case, and for the firs t time, a poleward surge of depletion/enhancement airglow zones was capture d by radar as well as an airglow imager. In the former case structures grew in place overhead and produced strong VHF F-region backscatter as observed by the CUPRI and University of Illinois radars; the other event, exactly o ne year later, did not result in detectable 3-m backscatter. The two data s ets show quantitatively that the low airglow region is elevated in height a nd depleted in plasma density and Pedersen conductivity. We suggest an enha nced eastward electric field inside the low conductivity zone may be respon sible for the surge. The data also suggest small scale turbulence can only be observed in developing structures.