Abstract
Coordinated measurements of equatorial spread‐F conducted during July 1979 at the Kwajalein Atoll have yielded the first definitive space‐ and time coincident radar and rocket observations of small scale irregularities and large scale plasma depletions. The results have shown that:(a) During conditions of well‐developed equatorial spread‐F the most intense "in situ" irregularities occurred on the bottomside F‐layer gradient.(b) Within a large scale topside F‐layer depletion radar backscatter and "in situ" irregularity strengths maximized near the depletion’s upper wall.(c) Ion composition within a topside depletion provided signatures of its bottomside source domain and estimates of average maximum vertical drift velocity. For long‐lived depletions, it was found that molecular‐ion signatures (NO+ and O2+) can be lost while bottomside levels of N+ can be maintained when [O+] ≈ Ne ≫ [NO+] + [O2+]; and finally,(d) Large scale fluctuations of O+ accompanied by a near‐constant level of NO+ and O2+on the bottomside F‐layer gradient suggests that neutral atmospheric turbulence is not a major source for bottomside ionospheric plasma irregularities and the associated triggering of equatorial spread‐F.
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