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Hanson, W. B.

Publications and source records attributed to Hanson, W. B..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The Martian ionosphere as observed by the Viking retarding potential analyzers

The first in situ measurements of the ionosphere of another planet were obtained by retarding potential analyzers of the Viking landers. These results are presented with attention to: (1) the determination of the peak ion concentration in the ionosphere layer at several altitudes, (2) the measurement of ion temperatures, and (3) an equatorward horizontal ion velocity observed at various heights. Both landers entered the ionosphere layer at solar zenith angles near 44 deg, and more structure was observed in the height profiles of ionospheric quantities on Viking 2, although the profiles were similar in shape to those of Viking 1.

Hanson, W. B.↗
NASA NTRS1977

Measurement of magnetic field aligned potential differences using high resolution conjugate photoelectron energy spectra

Simultaneous high-resolution observations of a distinctive feature in the energy spectrum of conjugate photoelectrons and spacecraft potential relative to the local ionosphere have allowed the net potential difference between magnetic conjugate points at latitudes below the region of low-energy (i.e., lower than 100 eV) auroral electron precipitation to be determined. Measurements made at 300 km from Atmosphere Explorer C show that there is normally no net potential difference between hemispheres in this region, which extended up to invariant latitudes as high as 74 deg. Two types of apparently related anomalous behavior were infrequently observed at high latitudes. During these periods the incident flux of conjugate photoelectrons was either decelerated by about 3 eV or was not detected.

Peterson, W. K.↗
NASA NTRS1977

Ion temperature troughs in the equatorial topside ionosphere

It is noted that the retarding potential analyzer aboard OGO 6 sometimes records pronounced minima of ion temperature when the satellite crosses the magnetic equator and that the variation of ion temperature along the satellite path takes the form of a trough about 20 to 30 deg wide in latitude and up to 1200 K in depth. Observations of night-time, daytime, and dawn-dusk ion-temperature troughs are discussed along with ion concentration and composition in the troughs, ion drift velocities, and comparisons with Jacchia's (1971) thermospheric model. An explanation of trough morphology is given in terms of thermospheric winds which produce a transequatorial plasma flow along geomagnetic field lines. The effect of such a plasma flow on 630-nm nightglow is considered, and it is shown how ion composition affects the extent of ion-temperature troughs. Some questions for further study are suggested.

Rishbeth, H.↗
NASA NTRS1977

Plasma bubbles and irregularities in the equatorial ionosphere

The Atmosphere Explorer satellite observed large-scale (10 to 200-km) irregular biteouts of up to three orders of magnitude in the ion concentration in the nighttime equatorial F region associated with small-scale inhomogeneities in the ion concentration. Simultaneous plasma velocity observations show irregular upward and westward motion of the order of 150 m/s associated with some of these 'bubbles', while others move more slowly or move with approximately the velocity of the background plasma. The plasma composition signatures indicate that most of the bubbles observed have recently moved upward. Several features of recent VHF radar observations can be understood as resulting from these plasma bubbles, e.g., the 'plume' features and very high apparent velocities seen on range-time-intensity spread F maps and the very complex and/or wide spectral features observed using such radars.

Mcclure, J. P.↗
NASA NTRS1977

Determination of the rate coefficient for the N2/+/ + O reaction in the ionosphere

Using approximately 400 simultaneous measurements of ion and neutral densities and temperatures, and the spectrum of the solar flux measured by the Atmosphere Explorer C satellite, we have determined the rate constant k1 for the reaction between N2(+) and O in the ionosphere for ion temperatures between 600 and 700 K. We find that k1 = 1.1 x 10 to the minus 10th power cu cm per sec, with a standard deviation of + or - 15%. If we use the temperature dependence for this reaction determined in the laboratory then at 300 K we find excellent agreement with the recommended laboratory value.

Torr, D. G.↗
NASA NTRS1977

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.↗
NASA NTRS1977

Electron and ion temperatures - A comparison of ground-based incoherent scatter and AE-C satellite measurements

The paper presents the results of comparisons of AE-C electron temperature of the ionosphere determined from the cylindrical electrostatic probe and the ion temperature of the ionosphere determined from the planar retarding potential analyzer with electron and ion temperatures determined from four incoherent scatter facilities: Arecibo, St. Santin, Millstone Hill, and Chatanika. Good agreement was obtained between the in situ and remote measurements of electron and ion temperatures. Longitudinal variations are found to be very important in the comparison of electron temperatures at some locations.

Benson, R. F.↗
NASA NTRS1976

Discrepancy between electron heating and cooling rates derived from Atmosphere Explorer-C measurements

The present theory of electron temperature in the daytime mid-latitude ionosphere is tested by using Atmosphere Explorer-C measurements. In the region below 300 km, where a balance is expected between electron heating by photoelectron impact and electron cooling to ions and neutrals, we find an imbalance in which the cooling rate is consistently higher than the heating rate. The shapes of the altitude profiles also differ substantially. The cooling rate has a sharp peak at about 220 km, while the heating rate exhibits a broad peak about 30 km lower. Improved agreement is achieved at higher altitudes by using an oxygen fine structure loss rate smaller by a factor of 2, based on more recent collision strength calculations. Although this improves the overall agreement of the heating and cooling rates, the shape discrepancy remains, and the new cooling rate falls consistently below the heating rate below 200 km.

Brace, L. H.↗
NASA NTRS1976

Composition and structure of the Martian atmosphere - Preliminary results from Viking 1

Results from the aeroshell-mounted neutral mass spectrometer on Viking 1 indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180 plus or minus 20 deg K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241 deg K. The descent data are consistent with the view that CO2 should be the major constituent of the lower Martian atmosphere.

Nier, A. O.↗
NASA NTRS1976

Comparison of neutral temperatures inferred from instruments on the AE-C satellite

Determinations of neutral thermospheric temperature from data taken with instruments aboard the AE-C spacecraft have been compared during the circular orbit phase in late December 1974 and January 1975 when the satellite altitude was near 260 km. These temperatures are found to be in overall agreement to within about 10% during periods of low magnetic activity. The methods are based on: analysis of the satellite spin modulation of N2 density; analysis of the ion temperature; and the calculation of the temperature needed to match measured N2 and Ar densities assuming fixed boundary conditions at 120 km.

Hedin, A. E.↗
NASA NTRS1976

Ion convection velocity reversals in the dayside cleft

Nearly simultaneous measurements of energetic particle precipitation and vector ion velocity have been made for the first time on Atmosphere Explorer C. These data have revealed the existence of both shear and rotational reversals in the ion convection velocity within the region of dayside cleft particle precipitation. The ion velocity data have shown that substantial regions of the dayside polar cap boundary are nearly electric equipotentials at which cleft particle precipitation is also observed but which cannot be identified with a merging region producing open field lines. Asymmetries in the polar cap flow, first implied by Heppner, may be determined by the extent and location of the equipotential boundaries.

Heelis, R. A.↗
NASA NTRS1976

Properties of spikelike shear flow reversals observed in the auroral plasma by Atmosphere Explorer C

A study of the characteristics of pairs of oppositely directed spikes in ionospheric convection velocities (or shear flow reversals), as first described by Gurnett, has been conducted by using data from Atmosphere Explorer C. These phenomena tend to occur near the large-scale reversal from sunward to antisunward convection on the nightside of the earth. Generally, the spikelike shear flow reversals involve electric field components along the spacecraft orbit that are directed toward the region between them, in which inverted V type electron precipitation is observed. This relationship between the electron precipitation and the electric field spikes is consistent with an upward-flowing field-aligned current that is fed by Pedersen currents from the adjacent regions of strong convection. In one case a divergent equivalent electric field structure was observed, that is, with the spikelike electric fields pointing away from the region in between, which in this case exhibited a sharp electron flux dropout. This opposite configuration may be an example of counterparts to inverted V structures existing in regions of downward-flowing field-aligned currents.

Burch, J. L.↗
NASA NTRS1976

Characteristics of auroral electron acceleration regions observed by Atmosphere Explorer C

Satellite measurements of electron precipitation and ion drift velocities showed that electron acceleration regions (or inverted V's) in the 1200 to 1800 MLT quadrant exhibit the following systematic behavior: electron distribution functions in the accelerated region can be well described by Maxwellian primary electron beams accelerated through an electrostatic potential; the typical inverted V latitudinal structure is always observed in the accelerated regions, the electrostatic potential reaching a maximum and consequently decreasing to near zero over distances of 100 to 250 km; the Maxwellian temperature of the primary electron beam increases systematically with increasing electrostatic potential; rather weak acceleration regions, characterized by values of the electrostatic potential below 1 keV and values of the Maxwellian temperature between 100 and 350 eV, occur in the cusp and in the highest-latitude portion of the dusk side electron precipitation zone.

Burch, J. L.↗
NASA NTRS1976

Recombination of NO/+/ in the ionosphere

Simultaneous nighttime measurements of ion and neutral concentrations and temperatures made by the Atmosphere Explorer-C satellite were used to determine the recombination rate coefficient of NO(+) as a function of electron temperature. The results agree in shape and absolute magnitude to within one standard deviation with those of Walls and Dunn (1974), indicating that NO(+) ions in the ionosphere may be in the ground vibrational state.

Torr, D. G.↗
NASA NTRS1975

Techniques for measuring bulk gas-motions from satellites

There is a growing appreciation for the dynamic nature of the upper atmosphere. This paper is concerned principally with discussing the methods for making in-situ measurements of the ambient gas velocities from satellites. Both neutral and ion instrumentation is discussed, but most attention is paid to the ion sensors on Atmosphere-Explorer-C, which are now providing the first detailed three-dimensional gas-velocity measurements from a satellite. While some data are presented, emphasis is placed on experimental difficulties and possible ways of alleviating these problems. It seems reasonable to expect that both neutral and ion gas velocities will be measured to an accuracy of the order of 20 m/s in future satellites, provided that a star tracker is available for the determination of vehicle attitude. The possible exception to this is the ram component of the neutral-gas velocity vector, for which no proven instrumentation yet exists.

Hanson, W. B.↗
NASA NTRS1975

Effects of atomic nitrogen on the nocturnal ionosphere

Recently, atomic nitrogen densities of 50-500 million/cu cm were inferred in the daytime thermosphere from studies of the NI(2D-4S) 5200 A emission and from the photochemistry of various ion species using data measured by the Atmosphere Explorer-C satellite. In this paper we use the photochemistry of NO(+) and O2(+) at night to determine nocturnal N(4S) densities in the thermosphere. We present evidence for a missing source of NO(+) and a missing sink for O2(+) at night and show that this can be adequately supplied by the reaction O2(+) + N yields NO(+) + O if the N density at 200 km is about 7 million/cu cm. The atomic nitrogen has an important effect on studies of the 6300 A airglow. The omission of N in calculations of O(1D) using ground-based data results in an overestimate of the rate coefficient for quenching of O(1D) by N2.

Torr, M. R.↗