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Journal of Geophysical Research



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During the Condor campaigna number of instrumentsw ere set up in Peru to supportt he rocket experimentsI.n this serieso f papersw e report on the resultso f the experimentsd esignedt o study the equatorial F region. In this overview paper we summarize the main results as well as report upon the macroscopicd evelopmentos f spreadF as evidencedb y data from backscatter ada•s,f rom scintillation observationsa,n d from digital ionosondem eaurementsIn. this latter regard,w e argueh ere that at least two factorso ther than the classicagl ravitationalR ayleigh-Taylorp lasmai nstabilityp rocessm ust operate to yield the longest-scalheo rizontalo rganizationo f spreadF structuresT. he horizontals calet ypical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow, althoughd etailedc omparisonw ith theorys eemsto requires hearf requencieas bit highert han observations indicate.O n the other hand, the largest-scaleo rganizationo r modulation of the scatteringl ayer cannotb e explainedb y the sheart heory and must be due to local time variationsi n the ionosphericd rift or to gravity wave inducedv erticalm otions.U sing simultaneousro cket and radar data, we were also able to confirm the oft quoted hypothesisth at rapid overheadh eight variationsi n the scatteringr egion over Jicamarcaa re primarily spatial structuresa dvectingo verhead.T he detailedr ocket-radarc omparison verified several other earlier results and speculationsp, articularly those made in the PLUMEX experimentIsn. particularc, ompanionp apersd iscussa nd extends omeo f the PLUMEX resultst o includet he role of anomalousd iffusion( LaBellee t al., this issuei)n the theoryo f equatorials preadF and to shedl ight upon the shallows pectralf orm often observedin the intermediate-scalree gime( LaBellea nd Kelley, this issue).