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The atomic hydrogen distribution at 250 km during December 1974 solstice has been inferred, considering charge exchange equilibrium, from Atmosphere Explorer-C measurements of n(H+), n(O+), and n(O). An empirical model, derived from the observations by least square analysis in terms of spherical harmonics, has the following characteristics: (a) n(H) increases by as much as a factor of two between the summer and winter hemispheres, (b) the n(H) diurnal variation is largest at the equator where nmax/nmin = 3.2, the maximum occurring at 03h LT, and (c) the diurnal variation is larger in the winter hemisphere ( nmax/nmin = 2.6 at +40°) than in the summer (nmax/nmin = 2.3 at −40°). Similar analysis of the gas temperature derived from n(N2) measurements reveals that all n(H) and Tg spherical harmonic coefficients are anticorrelated. Both the diurnal and latitudinal (annual) n(H) and Tg amplitudes are in substantial agreement with the “zero flux condition,” in which exospheric flow dominates the hydrogen distribution. The observed diurnal phase lag of n(H) with respect to Tg is about one hour, agreeing with theory. During the period of measurement the observed mean global values of Tg and n(H) were 800K and 3.6 × 105 cm−3, respectively, the latter exceeding the Kockarts-Nicolet model concentration by a factor of two.

The concentrations of neutral hydrogen, n(H), in the Venus atmosphere were derived from an ion and neutral charge exchange relationship involving O(+), H(+), O, and CO2, which were measured by OIMS and ONMS on board the Pioneer Venus for the period 1979-1980 covering three diurnal cycles of Venus. There was a persisting dawn bulge in the diurnal distribution of n(H), which peaked at levels near 5 x 10 to the 7th/cu cm at altitudes below 165 km. Large day-to-day variations of up to a factor of 5 in n(H) were frequently encountered, in addition to some local time variations in the bulge location. Although the appreciable short-term variability in n(H) makes precise assessment of the interannual variations difficult, no distinct evidence for interannual variation in n(H) was found. These results were confirmed by the facts that no significant interannual differences in n(H3) measured directly by ONMS were detected, and that only small (not more than 10 percent, decline) variations in the solar EUV flux were found in the 1979-1980 period.

Plasmasphere thermal positive ion structure, determining distribution of hydrogen and helium positive ions in magnetosphere from OGO

The Bennett spectrometer to be flown on Atmosphere Explorer-C and -E (AE-C and AE-E) is designed to measure, throughout the 120 to 4000-km orbit, the concentrations of all thermal positive ions in the mass range 1 to 72 amu and number density range 5 to 5,000,000 ions per cu cm. To reduce the buildup of ram pressure and facilitate measurements at low altitude, the analyzer is vented, and a multigrid ion-current collector is employed. An extensive command capability permits optimization of instrument parameters for particular measurement objectives; commandable functions include mass-scan range and period, the sensitivity-resolution characteristic of the analyzer, orifice potential, and in-flight calibration.

This is a preliminary report of atmospheric ion composition data obtained over Wallops Island, Virginia, from two successful Aerobee Hi rocket flights, serial numbers NASA 4.09 and NASA 4.14. These rockets were instrumented primarily to determine the composition, pressure, temperature, and density of the neutral particle atmosphere above 100 km. An ion composition experiment, identical for the two launchings, was also included as a part of the payload. Continuous ionosonde monitoring was provided by CRPL, Fort Belvoir, Virginia, and NATC, Patuxent Hiver, Maryland, during both firing periods.

A series of experiments conducted in December 1979 to investigate the structure of plasma depletions in the low latitude, nighttime ionosphere is discussed. Density biteouts of about one order of magnitude in the dominant ion, O(+), are mapped to lower altitudes along magnetic field lines for comparison with 6300-A and 7774-A O I airglow depletions. Owing to the different airglow production mechanisms (dissociative recombination of O2(+) for 6300 A and radiative recombination of O(+) for 7774 A), the 6300-A depletions reflect plasma depletions near the bottomside of the F layer, while those at 7774 A are located near the peak of the layer. The O(+) biteouts map directly into the 7774-A airglow depletions in the same hemisphere and also when traced into the opposite hemisphere, which suggests magnetic flux tube alignment over north-south distances of approximately 2220 km. The 6300-A (bottomside) depletions are found to be wider in longitude than the 7774-A (F-peak) depeletions near the equatorward edge of the Appleton anomaly.