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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Data acquired with the Geophysics Laboratory's high‐latitude meteor scatter test‐bed between Sondrestrom Air Base (AB) and Thule AB, Greenland, during the solar disturbances of March and August 1989 are presented. These disturbances provided a unique opportunity to observe a number of naturally occurring disturbance effects on meteor scatter links operated in the frequency range (35 to 147 MHz) covered by the test‐bed. The disturbances range from signal absorption to system noise variations. The properties of ionospheric absorption in general are discussed and illustrated with computations using electron density profiles from the September 1978 solar proton event (SPE). It has been found that accurate measurements of high levels of ionospheric absorption with riometers pose special problems. These problems are identified and discussed. The data acquired during the March and August 1989 solar disturbances are then related to the zenith absorption measured at Thule, and the influence of absorption as well as system noise variations are discussed. The two events presented are very different. The August event was dominated by ionospheric absorption which affected meteor arrival rates and duty cycles primarily at the lower frequencies (35 and 45 MHz), although some effects could also be seen at the higher frequencies (65 to 147 MHz). The March event combined weak ionospheric absorption with large solar noise bursts. The effects of this event on the test‐bed were dominated by increased solar noise at all frequencies. The relative influence of solar noise and ionospheric absorption during SPE events is discussed along with speculation as to the validity of frequency dependence conclusions based on testing of the JANET system.