The O+/2P/ emission at 7320 A in twilight
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Meriwether, J. W., Jr.↗
Engineering topics
Nier, A. O.
Publications and source records attributed to Nier, A. O..
Thermospheric variations as an indicator of magnetic storm heating and circulation
In situ measurements of the neutral constituent densities and temperature were made at 200 km by the open source mass spectrometer on the AE-D satellite during a rapid onset of the magnetic activity that occurred in January 1976. At high latitudes a 340 K temperature increase was accompanied by an increase in N2 and O2 concentrations, a decrease in He concentration, and a variable response in O concentration. At low latitudes, the rise in temperature was smaller, however; all constituent densities increased. It is concluded that the observed variations are consistent with heating and upward winds at high latitudes, meridional flow towards lower latitudes and subsidence near the equator.
Potter, W. E.↗
Quenching of metastable 2-D oxygen ions in the thermosphere by atomic oxygen
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Orsini, N.↗
Determination of the N2 recombination rate coefficient in the ionosphere
Measurements of aeronomic parameters made by the Atmosphere Explorer-C satellite are used to determine the recombination rate coefficient of N2(+) in the ionosphere. The rate is found to increase significantly with decreasing electron density. Values obtained range from approximately 1.4 x 10 to the -7th to 3.8 x 10 to the -7th cu cm/sec. This variation is explained in a preliminary way in terms of an increase in the rate coefficient with vibrational excitation. Thus, high electron densities depopulate high vibrational levels reducing the effective recombination rate, whereas, low electron densities result in an enhancement in the population of high vibrational levels, thus, increasing the effective recombination rate.
Orsini, N.↗
Composition and structure of Mars' upper atmosphere - Results from the neutral mass spectrometers on Viking 1 and 2
The upper atmospheric mass spectrometers flown on Viking 1 and 2 are described, and results obtained for the composition and structure of Mars' upper atmosphere are summarized. Carbon dioxide is the major constituent of the atmosphere at all heights below 180 km. The thermal structure of the upper atmosphere is complex and variable with average temperatures below 200 K for both Viking 1 and 2. The atmosphere is mixed to heights in excess of 120 km. The isotopic composition of carbon and oxygen in the Martian atmosphere is similar to that in the terrestrial atmosphere: N-15 is enriched in Mars' atmosphere by a factor of 1.62 + or - 0.16.
Nier, A. O.↗
The search for organic substances and inorganic volatile compounds in the surface of Mars
A total of four Martian samples, one surface and one subsurface sample at each of the two Viking landing sites, Chryse Planitia and Utopia Planitia, have been analyzed for organic compounds by a gas chromatograph-mass spectrometer. In none of these experiments could organic material of Martian origin be detected at detection limits generally of the order of parts per billion and for a few substances closer to parts per million. The evolution of water and carbon dioxide, but not of other inorganic gases, was observed upon heating the sample to temperatures of up to 500 C. The absence of organic compounds seems to preclude their production on the planet at rates that exceed the rate of their destruction. It also makes it unlikely that living systems that behave in a manner similar to terrestrial biota exist, at least at the two Viking landing sites.
Biemann, K.↗
Doubly charged atomic oxygen ions in the thermosphere. I - Photochemistry
Measurements of O(++) concentrations made by the Atmosphere Explorer C satellite are analyzed for altitudes where photochemical equilibrium conditions prevail in order to determine the photochemical sources and sinks of the doubly charged ion. The major loss process is found to be through partial charge exchange with neutral atomic oxygen with a rate coefficient of 1 x 10 to the -11th cu cm/s with an uncertainty of 40%. Above 220 km the major source is photo-ionization of O(+). However, X ray ionization of O (at not greater than 23.3 A) producing O(++) directly through the Auger process provides a better fit to the observed profile at lower altitudes.
Breig, E. L.↗
Intercomparison of neutral composition measurements from the satellite Esro 4, Aeros A, Aeros B, and Atmosphere Explorer C
Number-density data obtained at orbital 'crossover' points with the neutral-gas mass spectrometers aboard the Esro 4, Aeros A, AE-C, and Aeros B satellites are intercompared. All the mass spectrometers were designed to measure the ambient number densities of atomic oxygen, molecular nitrogen, helium, and argon. It is found that the agreement for N2 and O is satisfactory within the experimental errors and that the He measurements exhibit unexpectedly large discrepancies far outside the error range. Calibration and instrument sources of error are considered.
Trinks, H.↗
Empirical model of atomic nitrogen in the upper thermosphere
Atomic nitrogen number densities in the upper thermosphere measured by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer-C during 1974 and part of 1975 have been used to construct a global empirical model at an altitude of 375 km based on a spherical harmonic expansion. The most evident features of the model are large diurnal and seasonal variations of atomic nitrogen and only a moderate and latitude-dependent density increase during periods of geomagnetic activity. Maximum and minimum N number densities at 375 km for periods of low solar activity are 3.6 x 10 to the 6th/cu cm at 1500 LST (local solar time) and low latitude in the summer hemisphere and 1.5 x 10 to the 5th/cu cm at 0200 LST at mid-latitudes in the winter hemisphere.
Engebretson, M. J.↗
Planetary atmospheres with mass spectrometers carried on high-speed probes or satellites
Earth satellite-borne mass spectrometers are considered, taking into account the identification of atomic oxygen in the thermosphere with an 'open' source mass spectrometer flown on a sounding rocket, the conventional closed-source instrument, the mass spectrometers on the Atmosphere Explorer satellites, and mass spectrometer electron multiplier output. A description is presented of mass spectrometers and planetary entry probes. Attention is given to an attempt to obtain an atmospheric composition profile with a terrestrial entry probe, the descending trajectory in the early orbits of the Atmosphere Explorer C satellite, and the molecular nitrogen densities for the descending legs of the orbits. It is pointed out that chemical reactions on the surfaces of the mass spectrometer make the measurement of reactive atmospheric species such as atomic oxygen very difficult.
Nier, A. O.↗
Atomic nitrogen measurements in the upper thermosphere
The open source neutral mass spectrometer on board the Atmosphere Explorer satellites measures, besides other neutral constituents, atomic nitrogen densities in the upper thermosphere. Atomic nitrogen combines with atomic oxygen on the walls of the mass spectrometer ion source to form NO. From the measured NO concentration atomic nitrogen is deduced. Studies of the diurnal variation show that the maximum atomic nitrogen densities occur near 1600 local solar time (LST) and minimum densities near 0400 LST. The diurnal amplitude at 300 km is about a factor of 8, which is lower than predicted in present models. Atomic nitrogen also exhibits a pronounced seasonal variation with an amplitude similar to that of the diurnal variation; summer values are considerably higher than winter ones.
Mauersberger, K.↗
Composition and structure of the Martian upper atmosphere - Analysis of results from Viking
Densities for carbon dioxide measured by the upper-atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the Martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold, with average temperatures for both Viking 1 and Viking 2 of less than 200 K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.
Mcelroy, M. B.↗
Structure of the neutral upper atmosphere of Mars - Results from Viking 1 and Viking 2
Neutral mass spectrometers carried on the aeroshells of Viking 1 and Viking 2 indicate that carbon dioxide is the major constituent of the Martian atmosphere over the height range 120 to 200 kilometers. The atmosphere contains detectable concentrations of nitrogen, argon, carbon monoxide, molecular oxygen, atomic oxygen, and nitric oxide. The upper atmosphere exhibits a complex and variable thermal structure and is well mixed to heights in excess of 120 kilometers.
Nier, A. O.↗
Mass spectrometer with magnetic pole pieces providing the magnetic fields for both the magnetic sector and an ion-type vacuum pump
A mass spectrometer (MS) with unique magnetic pole pieces which provide a homogenous magnetic field across the gap of the MS magnetic sector as well as the magnetic field across an ion-type vacuum pump is disclosed. The pole pieces form the top and bottom sides of a housing. The housing is positioned so that portions of the pole pieces form part of the magnetic sector with the space between them defining the gap region of the magnetic sector, through which an ion beam passes. The pole pieces extend beyond the magnetic sector with the space between them being large enough to accommodate the electrical parts of an ion-type vacuum pump. The pole pieces which provide the magnetic field for the pump, together with the housing form the vacuum pump enclosure or housing.
Sieradski, L. M.↗
Recombination of O2/+/ in the ionosphere
In spite of the excellent agreement between various laboratory measurements of the recombination rate of O2(+) with electrons, it is still questionable whether the laboratory results apply in the ionosphere, because although the radiative lifetime of vibrating O2(+) is not well known, indications are that it may be very long. Whether the laboratory results apply in the atmosphere depends on whether the recombination rate is dependent on the vibrational state of the O2(+) ion and on whether the ions are deactivated (or not) in both the laboratory experiments and the atmosphere prior to recombination. To obtain reliable answers to these questions, the present study was carried out to determine the recombination of O2(+) in the ionosphere from in situ measurements of the relevant temperatures and densities made by the open source mass spectrometer carried by the AE-C satellite. The photochemistry involved is discussed. The results show that the ionospheric determination of the recombination rate of O2(+) with electrons agrees with the laboratory measurements of Walls and Dunn (1974) for electron temperatures between 1200 and 2000 K.
Torr, D. G.↗
Isotopic composition of the Martian atmosphere
Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of earth. Mars is enriched in N-15 relative to earth by about 75 per cent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO2 or H2O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of O-18.
Nier, A. O.↗
Isotopic composition of nitrogen - Implications for the past history of Mars' atmosphere
Models are presented for the past history of nitrogen on Mars, based on Viking measurements showing that the atmosphere is enriched in N-15. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2(+). The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.
Mcelroy, M. B.↗
Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars
Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500 C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts per billion by weight in the samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.
Biemann, K.↗