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Sharp, W. E.

Publications and source records attributed to Sharp, W. E..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

An assessment of twilight airglow inversion procedures using atmosphere explorer observations

The aim of this research project was to test and truth some recently developed methods for recovering thermospheric oxygen atom densities and thermospheric temperatures from ground-based observations of the 7320 A O(+)((sup 2)D - (sup 2)P) twilight air glow emission. The research plan was to use twilight observations made by the Visible Airglow Experiment (VAE) on the Atmosphere Explorer 'E' satellite as proxy ground based twilight observations. These observations were to be processed using the twilight inversion procedures, and the recovered oxygen atom densities and thermospheric temperatures were then to be examined to see how they compared with the densities and temperatures that were measured by the Open Source Mass Spectrometer and the Neutral Atmosphere Temperature Experiment on the satellite.

Mcdade, I. C.↗
NASA NTRS1991

A method for the retrieval of atomic oxygen density and temperature profiles from ground-based measurements of the O(+)(2D-2P) 7320 A twilight airglow

This paper describes a technique for extracting thermospheric profiles of the atomic-oxygen density and temperature, using ground-based measurements of the O(+)(2D-2P) doublet at 7320 and 7330 A in the twilight airglow. In this method, a local photochemical model is used to calculate the 7320-A intensity; the method also utilizes an iterative inversion procedure based on the Levenberg-Marquardt method described by Press et al. (1986). The results demonstrate that, if the measurements are only limited by errors due to Poisson noise, the altitude profiles of neutral temperature and atomic oxygen concentration can be determined accurately using currently available spectrometers.

Fennelly, J. A.↗
NASA NTRS1989

Atomic emission in the ultraviolet nightglow

An observation of the ultraviolet nightglow between 2670 A and 3040 A was conducted over White Sands Missile Range on October 22, 1984, at 0020 hours LST during the Orionids meteor shower. A 1/4-meter UV spectrometer operating at 3.5 A resolution viewed the earth's limb at tangent heights between 90 km and 110 km for 120 seconds. By inverting the observed limb intensities, a total zenith intensity of 1.4 kR is inferred for the Herzberg I system. Excess emission above the Herzberg I (7,3) band at 2852 A is identified as the Mg I resonance line. The intensity ratio of the Herzberg I band system to the 2972 A line from O(1S) was less than that predicted from the accepted O(1S) branching ratio and acceptable ratios of Herzberg I to 5577 A emissions. Arguments supporting the identification of the Herzberg III band system are also advanced.

Sharp, W. E.↗
NASA NTRS1987

In situ measurement of atomic hydrogen in the upper mesosphere

In situ measurements of H abundance between 73 and 93 km are reported for conditions of winter solstice, magnetic quiet, and a solar depression angle of 12 deg. The data were obtained by a rocket-borne instrument using the resonance fluorescence technique. A discharge source emitting photons at 1216 A was an integral part of the instrument. The instrument was radially deployed 80 cm by a boom from the front of the payload in order to avoid the shock created by the gas flow over the front of the payload. An attitude control system oriented the payload so that the gas flow was nearly perpendicular to the plane containing the incident and scattered photons, thus minimizing any correction for Doppler shift. The resonance radiation detector viewed a black backstop in order to minimize background radiation from the hydrogen geocorona; however, the background was not entirely eliminated. The signal-to-noise ratio was improved by summing the data in 1.8-s bins. The observed hydrogen concentration maximized at 85 km at 1.5 + or - 1.1 x 10 to the 8th atoms/cu cm.

Sharp, W. E.↗
NASA NTRS1986

Differential excitation cross section of atomic oxygen by electron impact - (3P-1D transition)

Results of an electron impact experiment in which a crossed-beam method was used to determine the differential excitation cross sections of atomic oxygen (3P-1D transition) are reported. The measurements cover energies of 7, 10, 15, 20, and 30 eV, with the angular range varying from 30 to 150 deg in 15-deg increments. The results are consistent, both in shape and in magnitude, with theoretical predictions, providing a direct confirmation of the theoretical total excitation cross sections of O(1D) state. Details of the experimental equipment and procedure are given.

Shyn, T. W.↗
NASA NTRS1985

Upper limits to (O) in the lower thermosphere from airglow

A method for estimating the upper limit to oxygen atom density in the lower thermosphere is presented. The method is based on an analytical equation for the energy density of recombination process, and the radiation of O2 atoms at excited levels. As an example of the method, upper limits of oxygen atom density are estimated for the CIRA (O2) reference atmosphere of 1972. The estimates are given in a table.

Sharp, W. E.↗
NASA NTRS1985

Definition phase for thermal ion dynamics experiment for OPEN

The Thermal Ion Dynamics Experiment (TIDE) combines differential measurements of angle, energy, and mass to determine the detailed distribution function of low energy magnetospheric ions in the range of 0 to 100 eV. Goals included designing a 1 sq cm entrance aperture, minimizing trajectory divergence at exist aperture, and minimizing internal scattering. Design parameters were used to construct the test model.

Sharp, W. E.↗
NASA NTRS1984

On the temperature dependence of the reaction O+NO-NO2(asterisk)

The published data on the temperature dependence of the radiative combination of atomic oxygen with nitric oxide at pressures near 1 torr is examined. Arguments are advanced to suggest that radiation near the cut-off wavelength (about 3875A) is coming from the unstabilized activated complex, NO2(asterisk). At 4000A a positive activation energy of 1 kcal/mole is deduced. Application of this temperature dependence with the rate coefficient at 5200A is made to airglow measurements in aurora. The deduced NO concentration is about 10 to the 9th per cu cm, in general agreement with that deduced from the measured NO(+)/O2(+) ratio as well as an auroral model prediction.

Sharp, W. E.↗
NASA NTRS1983

The dissociative recombination of O2(+) - The quantum yield of O(1S) and O(1D)

Data from the visible airglow experiment on the Atmosphere Explorer-E satellite have been used to determine the quantum yield of O(1S) and O(1D) from the dissociative recombination of O2(+). A range of values between 0.09 and 0.23 has been obtained for the quantum yield of O(1S). It is shown that the quantum yield of O(1S) depends on the ratio of electron density to atomic oxygen density. This suggests that the quantum yield of O(1S) may depend on the degree of vibrational excitation of the recombining O2(+). The quantum yield of O(1D) has been measured to be 1.23 + or - 0.42, with no dependence on the electron-oxygen ratio.

Abreu, V. J.↗
NASA NTRS1983

Concerning sources of O/1D/ in Aurora - Electron impact and dissociative recombination

The present investigation is concerned with two questions. One is related to the possibility that the O(1D) level is produced by an as yet unidentified process in aurora. The second question is concerned with the need for an additional source and the altitude over which it is required. The data base of the AE satellite (AE-D in particular) was examined for this study. It is found that dissociative recombination and electron impact are inadequate sources of O(1D) in aurora. Nearly 90% of the source function is unidentified below 200 km and about 55% is missing above 250 km. The possibility that thermal electron impact could provide the missing source above 250 km was examined. Calculations showed that the missing source above 250 km could be explained by thermal electron impact if the electron temperatures were approximately 2900 K.

Sharp, W. E.↗
NASA NTRS1982

Suprathermal electrons produced by beam-plasma-discharge

Experiments conducted with a low energy plasma lens, HARP, in the electron beam of the large vacuum chamber at Johnson Space Center indicate that an enhanced population of 50 to 300 volt electrons appear when the beam goes into the Beam-Plasma Discharge (BPD) mode. Below the BPD instability the electron distribution appears to be characterized as non-energized single particle scattering and energy loss. At 100 cm from the beam core in the BPD mode the fluxes parallel to the beam are reduced by a factor of 20 with respect to the fluxes at 25 cm. Some evidence for isotropy near the beam core is presented.

Sharp, W. E.↗
NASA NTRS1981

Nitric oxide delta band emission in the earth's atmosphere - Comparison of a measurement and a theory

Attention is given to the altitude dependent emission rate in the delta-bands of nitric oxide as measured in the earth's atmosphere at night by a scanning ultraviolet spectrometer. It is noted that the reaction responsible is the two-body association of nitrogen and oxygen atoms. The measurements show a vertical intensity beneath the layer for the delta-band system of 19 R. The horizontal emission rate is found to increase from 70 R at 117 km to 140 R at 150 km. The data are analyzed with a one-dimensional, time-dependent, vertical-transport model of odd nitrogen photochemistry. The calculated and measured intensities agree so long as the quenching of N(2D) by atomic oxygen is near 5 x 10 to the -13 cu cm/sec.

Rusch, D. W.↗
NASA NTRS1981

Chemiluminescence of nitric oxide

Measurements of the intensities of the delta and gamma bands of nitric oxide in the nighttime terrestrial thermosphere are presented and used to infer the rate coefficient for the transition from the C 2 Pi to the A 2 Sigma + states. The nightglow spectrum was observed between 1900 and 2300 A at a resolution of 15 A by a rocket-borne scanning 1/4-m spectrometer pointing north at an apogee of 150 km. Progressions of the delta, gamma and epsilon bands are identified on the spectra by the construction of synthetic spectra, and the contributions of resonance fluorescence to the total band intensities are calculated. Finally, the ratio of the sum of the gamma bands for v-prime = 0 to the sum of the delta bands for v-prime = 0 is used to derive a branching ratio of 0.21 + or - 0.04 to the A 2 Sigma + state, which yields a probability for the C-A transition of 5.6 + or - 1.5 x to the 6th/sec.

Sharp, W. E.↗
NASA NTRS1981

Determining the electron energy distribution near the plasma potential in the earth's ionosphere

A determination of the plasma potential using an electrostatic analyzer is described in which the potential difference between the instrument slit system and surrounding plasma is minimized. Data obtained from rocket-borne instrumentation demonstrate the viability of this technique for electron fluxes between thermal energies (about 0.5 V) and suprathermal energies (many volts).

Sharp, W. E.↗
NASA NTRS1980

The swept angle retarding mass spectrometer: Initial results from the Michigan auroral probe sounding rocket

Data from a sounding rocket flight of the swept angle retarding ion mass spectrometer (SARIMS) are presented to demonstrate the capability of the instrument to make measurements of thermal ions which are differential in angle, energy, and mass. The SARIMS was flown on the Michigan auroral probe over regions characterized first by discrete auroral arcs and later by diffuse precipitation. The instrument measured the temperature, densities, and flow velocities of the ions NO(+) and O(+). Measured NO(+) densities ranged from 10 to the 5th power up to 3 x 10 to the 5th power ions/cu cm, while the measured O(+) densities were a factor of 5-10 less. Ion temperatures ranged from 0.15 up to 0.33 eV. Eastward ion flows approximately 0.5 km/sec were measured near the arcs, and the observed flow magnitude decreased markedly inside the arcs.

Reasoner, D. L.↗
NASA NTRS1980

Absolute concentrations of O/3P/ in the lower thermosphere at night

A rocketborne instrument module for detecting atomic oxygen concentrations by the resonance fluorescence technique is reported. The module contained a source lamp emitting O I 1304 A photons and a detector for the scattered photons. The module was constructed so that it could be coupled to a fast flow reactor for calibration purposes. During the flight the module was radially deployed from the payload on an oscillating boom with a maximum extension of 90 cm from the skin. Analysis of the initial flight data indicates that the shock formed by the motion of the rocket had a substantial effect on the data and the maximum concentration of the layer at 93 km was about 1.1 x 10 to the 11th/cu cm.

Sharp, W. E.↗
NASA NTRS1979

The concentration of atomic oxygen in the auroral lower thermosphere

A method is described to determine the concentration of atomic oxygen in the altitude range 100 to 160 km in an aurora from the ratio of the volume emission rates of the O(1S) 5577 A to N2(+) in 3914 A emissions. Applying the technique to previously published measurements it is found that the O density at 100 km is typically about 1 x 10 to the 11th per cu cm. The occurrence of densities in excess of 2 x 10 to the 11th per cu cm in the aurora at 100 km is rare.

Torr, D. G.↗