A quadrupole mass spectrometer system employing a liquid nitrogen chilled zeolite pump has recently been developed for sampling positive ions at altitudes above 50 km. This system was flown successfully on a Nike Cajun rocket on October 31, 1963, at local noon from Eglin Air Force Base, Florida, and has provided the first positive ion composition measurements in the D region. The predominant ions detected within the D region (64 to 82 kin) were 19', 30 +, and (37 q-1)+, with 32 + rapidly rising above 75 km approaching the abundance of 30* at 83 km. At 82.5 km a sharp transition occurred in the spectrums, characterized by the rapid disappearance of 19 + and 37 + and instantaneous appearance of six new ion peaks. Five of these ion peaks are suggested to be the metallic ions of sodium (239, magnesium (24 +, 25', 269, and calcium (40+). The metallic ions all exhibited an identical altitude profile: a 10-kinwide peak with a maximum at 95 km, a minimum at 105 km, and then a continuous increase until apogee at 112 km. Above 82 km the ions 30 + and 32 + appear to be the most predominant, although many other minor constituent ions are present. INSTRUMENTATION Ro.cket payload. A Nike Cajun rocket payload (AFCRL No. AC 6.341) was instrumented at the Air Force Cambridge Research Laboratories to measure the positive ion composition and the position ion, negative ion, and electron number densities of the D region and lower E region of the ionosphere. The instrument package contained a quadrupole mass filter system and two spherical electrostatic probes. (This report will present the positive ion composition results; the complete results and details of the electrostatic probe measurements will be published shortly by R. C. Sagalyn and M. Smiddy.) For rocket aspect information, two magnetometers were mounted parMlel and transverse to the longitudinal axis of the payload. A complete aspect sensor system could not be fitted into the package because of lack of space. A standard two-watt FM-FM telemeter transmitter with 3687 3688 NARCISI AND BAILEY 2,12" 5 •/e"

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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.

Detailed computer calculations of the electron, O2+, and NO+ concentrations are provided for the E region on a diurnal basis. The present work contains the first continuous solution of these concentrations during sunrise and sunset. Comparison is made between this model and observations, particularly new results at sunrise and sunset. The model is compatible with the experimental data within a factor of 2, although some larger discrepancies occur. The nitric oxide distribution of Barth for altitudes 90–120 km appears to provide for the proper amount of conversion of O2+ into NO+ via O2+ → NO+ → NO+ + O2 and for an important twilight ionization source, H Ly α + NO → NO+ + e. However, at 85 km, the model requires a lower concentration of nitric oxide than found by Barth in order to be consistent with the observed charged particle concentrations. The process N(²D) + O2 → NO + O is considered as a major NO‐producing process in the E region. The most abundant atomic nitrogen species, N (4S), appears to play no role in the E region, except perhaps at 130 to 140 km. An upper limit of about 108 cm−3 is implied for atomic nitrogen. The calculations include H Ly β as the main nighttime ionization source. It is stressed that the mean recombination coefficient of the E region appears to be larger at night than by day and largest at twilight.