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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Observations of neutral circulation at mid-latitudes during the Equinox Transition Study

Measurements of ion drift velocity made by the Millstone Hill incoherent scatter radar have been used to calculate the meridional neutral wind velocity during the Sept. 17 to 24, 1984 period. Strong daytime southward neutral surges were observed during the magnetically disturbed days of September 19 and 23, in contrast to the small daytime winds obtained as expected during the magnetically quiet days. The surge on September 19 was also seen at Arecibo. In addition, two approaches have been used to calculate the meridional wind component from the radar-derived height of the F-layer electron density peak. Results confirm the wind surge, particularly when the strong electric fields measured during the disturbed days are included in the calculations. The two approaches for the F-layer peak wind calculations are applied to the radar-derived electron density peak height as a function of latitude to study the variation of the southward daytime surges with latitude.

Buonsanto, M. J.↗
NASA NTRS1988

Full configuration-interaction study of the ionic-neutral curve crossing in LiF

Full configuration-interaction (FCI) calculations are used to assess the relative ability of methods for truncating the n-particle expansion in describing the ionic-neutral curve crossing between the two lowest Sigma(+) states of LiF. While the FCI calculations yield a smooth dipole moment function, MRCI calculations based on CASSCF orbitals optimized for the lowest state at all r values yield a discontinuous dipole moment function. However, when the orbitals are optimized using a state-averaged CASSCF procedure, with equal weights for the ionic and neutral solutions, both the CASSCF and MRCI dipole moment functions are smooth and in reasonable agreement with the FCI. No single-reference-based method is found to work satisfactorily. Potential curves for the lowest two Sigma(+) states are determined in both the adiabatic and diabatic representations using a large atomic natural orbit Gaussian basis set and a state-averaged CASSCF/MRCI treatment of electron correlation.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1988

Wavelike perturbations observed in the neutral thermosphere of Venus

Wavelike perturbations are evident in the neutral thermosphere measurements of He, N, O, N2, and CO2 by the Pioneer Venus orbiter neutral mass spectrometer. In the wavelength range from 100 to 600 km, the amplitudes of the various species are comparable in magnitude, with CO2 having the largest amplitude, and with helium out of phase with respect to the heavier species. On the dayside, the small-scale variations of CO2 and N2 increase with increasing altitude from 170 to 210 km, with CO2 having the largest slope. Simple and complex wave structures are observed, including wave trains and pulselike events. There is more activity during nighttime than during daytime, and larger values of the activity occur in the vicinity of the predawn and postdusk terminator sectors. Below 160 km, the standard deviation of the CO2 density on the nightside is 12 percent, about 3 times the daytime value. The data are consistent with the interpretation that the density perturbation are due to gravity waves propagating upward from the lower thermosphere.

Kasprzak, W. T.↗
NASA NTRS1988

Scattering of sodium D photons by neutral gas in the planetary nebula BD +30 deg 3639

Observations of the planetary nebula BD +30 deg 3639 are presented. It is shown that the Na DS photons emitted by the central star of the nebula are scattered by a neutral circumnebular envelope. These observations demonstrate the utility of optical absorption lines as tracers of the neutral material associated with planetary nebulae.

Dinerstein, Harriet L.↗
NASA NTRS1989

The heliospheric neutral hydrogen density profile in the presence of a solar wind shock

The effect of a postulated nearby solar wind shock on the radial density profile of the cold inflowing neutral hydrogen atoms is studied. It is found that a nearby solar wind shock strongly affects the neutral hydrogen breeze. Model calculation reveals that the strongly perturbed hydrogen atom distribution beyond a solar wind shock can be remotely detected by observation of the radial dependence of the backscattered UV glow from the deep space probes Pioneer 10/11 and Voyager 1/2.

Gangopadhyay, P.↗
NASA NTRS1989

The neutral cloud and heavy ion inner torus at Saturn

Voyager plasma data are used in conjunction with laboratory data on water molecule sputter-yields and energy distributions to calculate the morphology of the Saturn neutral water molecule and dissociated water molecule-product torus coexisting with the E-ring and icy satellites of this planet. Plasma production rates determined for this cloud exhibit a structure with distance from Saturn as well as from the orbit plane; this suggests a lack of equilibrium for the heavy ion plasma at less than 7 planet radii. Attention is given to the possibility that the Saturn E-ring may be a precipitate of the neutral cloud that is initiated by low-energy ion-molecule reactions.

Johnson, R. E.↗
NASA NTRS1989

Laboratory simulation of cometary neutral gas ionization

The laboratory simulation of the interaction of the solar wind with a comet is used to study the cometary neural gas ionization. The experiment is carried out in the UCR T-1 facility with an ice ball as the comet model. Photographs and data are taken with a variety of values of the solar wind velocity, interplanetary magnetic field (IMF), and comet configurations. The results show that the cometary neutral gas ionization depends on both the velocity of the solar wind and the interplanetary magnetic field. The plasma cloud surrounding the comet is visible only when the solar wind velocity and IMF are both above certain minimum values. This velocity dependent phenomena is explained by Alfven's critical ionization velocity effect. The critical magnetic field may be explained by assuming two stream lower hybrid instability as a triggering mechanism for the ionization of the neutral gas by plasma flow. Critical upper and lower limits for the magnetic field, required by anomalous ionization, are also derived that satisfy the experimental observations.

Chang, Tsuey-Fen↗
NASA NTRS1989

High-current plasma contactor neutralizer system

A plasma-contactor neutralizer system is described, for the stabilizing the Orbiter's potential during flights of the Atmospheric Laboratory for Applications and Science missions. The plasma contactor neutralizer will include a Xe plasma source that can provide steady-state ion-emission currents of up to 1.5 A. The Orbiter's potential will be maintained near that of the surrounding space plasma during electron-beam accelerator firings through a combination of ion emission from the Xe plasma source and electron collection from the ambient space plasma. Configuration diagrams and block diagrams are presented along with the performance characteristics of the system.

Beattie, J. R.↗
NASA NTRS1989

Collisionless reconnection in a quasi-neutral sheet near marginal stability

Particle simulations are used to investigate the process of collisionless reconnection in a magnetotail configuration which includes a pressure gradient along the tail axis and tail flaring. In the absence of electron stabilization effects, the tearing mode is stabilized when the ion gyrofrequency in the normal field exceeds the growth rate in the corresponding one-dimensional current sheet. The presence of a low-frequency electromagnetic perturbation in the lobes can serve to destabilize a marginally stable current sheet by producing an extended neutral-sheet region which can then undergo reconnection. These results help to explain how X-type neutral lines, such as those associated with the onset of magnetospheric substorms, can be formed in the near-earth plasma sheet.

Pritchett, P. L.↗
NASA NTRS1989

Simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval

Results are presented on simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval, carried out during a chemical release experiment on March 21, 1987. The observed plasma drifts and electron densities indicated the presence of a significant coupling between plasma and neutrals at the altitude of the F region but little coupling in the lower E region. The wind variations in the height range between 95 and 130 km were suggestive of the variations and amplitudes expected if the flow was dominated by the semidiurnal tide. However, a comparison of the flow with the model developed by Forbes (1982) showed that the phase differs by 4-5 hours from the predictions. Moreover, the measured divergence and vorticity in the flow are much larger than those predicted by the model, indicating that higher-order modes than those treated by Forbes may contribute significantly to the high-latitude thermospheric flow.

Larsen, M. F.↗
NASA NTRS1990

Neutral winds derived from IRI parameters and from the HWM87 wind model for the SUNDIAL campaign of September, 1986

Meridional neutral winds derived from the height of the maximum ionization of the F2-layer are compared with values from results of the HWM87 empirical neutral wind model. The time period considered in this study is the SUNDIAL-2 campaign, September 21 through October 5, 1986. Winds have been derived from measurements by a global network of ionosondes, as well as from similar quantities generated by the International Reference Ionosphere. Global wind patterns from the three sources are similar. Differences tend to be the result of local or transient phenomena that are either too rapid to be described by the order of harmonics of the empirical models, or are the result of temporal changes not reproduced by models based on average conditions.

Miller, K. L.↗
NASA NTRS1990

Response of Venus exospheric temperature measured by neutral mass spectrometer to solar EUV flux measured by Langmuir probe on the Pioneer Venus orbiter

The photoelectron current from the Pioneer Venus Langmuir probe has provided measurements of the total flux of solar EUV photons at Venus since 1979. The neutral oxygen scale height measured by the orbiter neutral mass spectrometer has permitted the exospheric temperature to be derived during the same mission. In this paper, the EUV observations are used to examine the response of exospheric temperature to changes in solar activity, primarily those related to solar rotation. It is found that the dayside exospheric temperature quite faithfully tracks variations in the EUV flux. Comparison is also made with the earth-based solar activity index F10.7 adjusted to the position of Venus. This index varied from 142 to 249 flux units during the period of measurements. The exospheric temperature is better correlated with EUV flux than with the 10.7-cm solar radio flux.

Mahajan, K. K.↗
NASA NTRS1990

Low-latitude thermospheric neutral winds determined from AE-E measurements of the 6300-A nightglow at solar maximum

Atmosphere Explorer E (AE-E) measurements of the O(1D) 6300-A emission in the nighttime equatorial thermosphere are used to infer the height of the F2 layer peak as a function of latitude and local time. The investigation is conducted both for northern hemisphere winter solstice and for spring equinox, under solar maximum conditions. The layer heights are used to derive magnetic meridional components of the transequatorial neutral wind, in conjunction with the MSIS-86 model and previous Jicamarca incoherent scatter measurements of the zonal electric field. The AE-E wind estimates indicate a predominant summer to winter flow for the winter solstice case. Comparisons are made with the empirical horizontal wind model HWM87 and with winds generated by the thermospheric general circulation model. The model predictions and experimental results are generally in good agreement, confirming the applicability of visible airglow data to studies of the global neutral wind pattern.

Burrage, M. D.↗
NASA NTRS1990

Thermal structure of neutral winds from young stellar objects

The physical processes that control the thermal structure of lightly ionized winds from cool protostars are discussed. Attention is concentrated on the hydrogen gas, and the heating, cooling, and chemical processes that affect the neutral and ionic species of atomic and molecular hydrogen are examined. Warm silicate dust may condense out of the cooling wind and may heat the gas through collisions. Singly ionized sodium atoms, which do not recombine for the mass-loss rates considered, set a lower limit to the ionization fraction in the wind. Magnetic fields, which are presumed to accelerate the wind, couple directly to the ionic component of the gas and transfer momentum and energy to the neutral component through collisions. This process of ambipolar diffusion is found to be the dominant source of heat input to the gas.

Ruden, Steven P.↗
NASA NTRS1990

Neutral winds derived from IRI parameters and from the HWM87 wind model for the sundial campaign of September, 1986

Meridional neutral winds derived from the height of the maximum ionization of the F2 layer are compared with values from results of the HWM87 empirical neutral wind model. The time period considered is the SUNDIAL-2 campaign, 21 Sept. through 5 Oct. 1986. Winds were derived from measurements by a global network of ionosondes, as well as from similar quantities generated by the International Reference Ionosphere. Global wind patterns from the three sources are similar. Differences tend to be the result of local or transient phenomena that are either too rapid to be described by the order of harmonics of the empirical models, or are the result of temporal changes not reproduced by models based on average conditions.

Miller, K. L.↗
NASA NTRS1989

Dust clouds in Orion and the interstellar neutral hydrogen distribution

According to published examples of the far IR observations in the Orion and its surroundings, several well defined dust clouds of different sizes and structure are present. For comparison of these clouds with the neutral hydrogen distribution on the area of approx. 1000 sq degs, the data from Pulkovo Sky Survey in the interstellar neutral Hydrogen Radio Line as well as special observations with the RATAN-600 telescope in 21 cm line were used. From the materials of Pulkovo HI Survey, the data were taken near the line emission at ten velocities between -21.8 and +25.6 km/s LSR for the structural component of the interstellar hydrogen emission. The results given concern mainly the Orion's Great Dust Cloud and the Lambda Orionis region where the information about the situation with the dust and interstellar hydrogen is very essential for interpretation.

Bystrova, N. V.↗
NASA NTRS1990

Effects of neutral gas releases on electron beam injection from electrically tethered spacecraft

The presence of high neutral densities at low altitudes and/or during thruster firings is known to modify the spacecraft potential during active electron beam injection. Two-dimensional (three velocity) particle simulations are used to investigate the ionization processes including the neutral density required, the modification of the spacecraft potential, beam profile and spatial distribution of the return current into the spacecraft. Three processes are identified: (1) beam-induced ionization, (2) vehicle-induced ionization, and (3) beam plasma discharge. Only in the first two cases does the beam propagate away with little distortion.

Winglee, R. M.↗
NASA NTRS1991

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

Vaughn, J. A.↗