Engineering topics
Publications and source records attributed to Hays, P. B..
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).
An array of 5 autonomous spectrometers, the imaging spectrometric observatory covers a broad wavelength range (approximately 200 to 12,000 A), has a resolution selectable down to approximately 0.5 A, and a dynamic range of approximately 10 to the 7th power and is designed to select experiment measurement sequences by software control. Because current models of thermospheric ionic processes produce too much N2(+) ionization, the N2(+) reaction with O and the chemistry of metastable (N(+) ions and of O2(+) ions are objects of study on Spacelab 1.
An investigation has been completed to determine the effects of prolonged exposure to cosmic radiation on Zerodur spacing elements used between two dielectric reflectors on silica substrates in the plane Fabry-Perot etalon selected for flight in the Dynamics Explorer satellite. The measured radiation expansion coefficient for Zerodur is approximately -4.0 x 10 to the -12th/rad. In addition to the overall change in gap dimension, test data indicate a degradation in etalon parallelism, which is ascribed to the different doses received by the three spacers due to their differing distances from a Co-60 source. The effect is considered to be of practical use in the tuning and parallelism adjustment of fixed gap etalons. The variation is small enough not to pose a problem for the satellite instrument where expected radiation doses are less than 10,000 rads.
A series of twilight interferometric observations of the near infrared O(+)(2P) doublets at 7320 and 7330 A between April 1979 and October 1979 detected excessive amounts of emission at shadow heights above 550 km. The scale height deduced from the vertical brightness profile determined from data taken on September 26, 1979, when the 10.7-cm flux was 231, showed a marked increase above 550 km. The equivalent temperature was estimated to be 4000 K or higher. Observations of the emission line shape with the high-resolution capability of the interferometer substantiated these results by a very apparent progressive broadening of the emission profile between times of low and high shadow height. It is concluded from these results that there exists an atomic oxygen corona overlying the thermosphere during the solar maximum period.
At high-latitude regions, energetic oxygen atoms are produced by a nonthermal mechanism associated with precipitated energetic atomic oxygen ions during disturbed periods. The upward moving nonthermal atoms can redistribute themselves at higher altitudes. For the storm of December 17, 1971, assuming the energetic O(+) ions are uniformly precipitated between 50 deg and 70 deg magnetic latitudes, the nonthermal oxygen atoms become dominant over the ambient at about 700 km on the dayside and at about 600 km on the nightside at 60 deg magnetic latitude. Globally, a high-number-density atomic oxygen corona appears between 50 deg and 70 deg magnetic latitudes above the exobase, and the maximum is located at a few degrees poleward from the center of the band (63 deg magnetic latitude).
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The paper presents a model of global atmospheric electricity used to examine the effect of upper atmospheric generators on the global electrical circuit. The model represents thunderstorms as dipole current generators randomly distributed in areas of known thunderstorm frequency; the electrical conductivity in the model increases with altitude, and electrical effects are coupled with a passive magnetosphere along geomagnetic field lines. The large horizontal-scale potential differences at ionospheric heights map downward into the lower atmosphere where the perturbations in the ground electric field are superimposed on the diurnal variation. Finally, changes in the upper atmospheric conductivity due to solar flares, polar cap absorptions, and Forbush decreases are shown to alter the downward mapping of the high-latitude potential pattern and the global distribution of fields and currents.
The Visible Airglow Experiment on the Atmosphere Explorer E satellite has observed the resonantly scattered emission from Mg II at 2800 A in the equatorial ionosphere. Altitude profiles of the Mg(plus) ion distribution have been obtained from the inversion of the surface brightness measurements made on spinning orbits. These data show a daytime metallic ion layer between 150 and 200 km developing in the early morning and reaching about 100 ions/cu cm in the afternoon. Mg(plus) ions are also seen in the F 2 region mostly in the late afternoon hours within a few degrees of the dip equator. The study of the vertical column density measured in the despun mode indicates that the amount of Mg(plus) in the F region is most variable in the afternoon hours at low dip latitudes. These results can be explained in part by the diurnal variation of the E x B drift velocity which lifts the metallic ions up into the F region. The observations suggest that the vertical polarization electric field is not the primary transport mechanism extracting the Mg(plus) ions from the low-altitude source layer.
The rise of atmospheric O3 as a function of the evolution of O2 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of Ox(O3, O, O(1D)), N2O, NOx(NO, NO2, HNO3), H2O, and HOx(H, OH, HO2, H2O2) including the effect of vertical eddy transport on the species distribution. The total O3 column density was found to maximize for an O2 level of 0.1 present atmospheric level (PAL) and exceeded the present total O3 column by about 40%. For that level of O2, surface and tropospheric O3 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. It was also found that in the O2-deficient paleoatmosphere, N2O (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere.
A quasi-steady model of global lower atmospheric electricity is presented. The model considers thunderstorms as dipole electric generators that can be randomly distributed in various regions and that are the only source of atmospheric electricity and includes the effects of orography and electrical coupling along geomagnetic field lines in the ionosphere and magnetosphere. The model is used to calculate the global distribution of electric potential and current for model conductivities and assumed spatial distributions of thunderstorms. Results indicate that large positive electric potentials are generated over thunderstorms and penetrate to ionospheric heights and into the conjugate hemisphere along magnetic field lines. The perturbation of the calculated electric potential and current distributions during solar flares and subsequent Forbush decreases is discussed, and future measurements of atmospheric electrical parameters and modifications of the model which would improve the agreement between calculations and measurements are suggested.
There are a number of measurements of electrical variations that suggest a solar-terrestrial influence on the global atmospheric electrical circuit. The measurements show variations associated with solar flares, solar magnetic sector boundary crossings, geomagnetic activity, aurorae, differences between ground current and potential gradients at high and low latitudes, and solar cycle variations. The evidence for each variation is examined. Both the experimental evidence and the calculations made with a global model of atmospheric electricity indicate that there is solar-terrestrial coupling through atmospheric electricity which operates by altering the global electric current and field distribution. A global redistribution of currents and fields can be caused by large-scale changes in electrical conductivity, by alteration of the columnar resistance between thunderstorm cloud tops and the ionosphere, or by both. If the columnar resistance is altered above thunderstorms, more current will flow in the global circuit, changing the ionospheric potential and basic circuit variables such as current density and electric fields. The observed variations of currents and fields during solar-induced disturbances are generally less than 50% of mean values near the earth's surface.
Satellite observations of the optical emission features in the aurora and nighttime airglow are usually contaminated by scattering from clouds and snow. It is shown here that this contamination can easily be removed when the emission layer is viewed against a surface of known albedo. The effect of the earth's curvature, parallax, and varying image angle are found to be significant but can be removed from the observation.
The production and destruction of O(D-1) atoms in the thermosphere are studied on the basis of observations conducted by the Atmosphere Explorer-C spacecraft. In particular, measurements of the O I transition at 6300 A provide a means of calculating the strength of the O2(+) dissociative recombination source of O(D-1), which amounts to 1.33. A value of 3 times 10 to the minus 11th power cu cm/sec is established for the quenching rate of O(D-1) by molecular nitrogen, while the photodissociation rate for O2 is set at three millionths per sec. These determinations are in agreement with the conventional theory of the day 6300-A airglow.
The visible airglow experiment on the Atmosphere Explorer-C satellite has gathered sufficient data over the earth's polar regions to allow one to map the geographic distribution of particle precipitation using emissions at 3371 and 5200 A. Both of these features exhibit large variations in space and time. The 3371 A emission of N2(C cubed pi), excited by low energy electrons, indicates substantial energy inputs on the dayside in the vicinity of the polar cusp. More precipitation occurs in the morning than evening for the sample reported here, while the entire night sector between magnetic latitudes 65 and 77.5 deg is subjected to particle fluxes. Regions of enhanced 5200 A emission from N(D-2) are larger in horizontal extent than those at 3371 A. This smearing effect is due to ionospheric motions induced by magnetospheric convection.
Analysis of data obtained by the backscatter ultraviolet (BUV) experiment on the Atmosphere Explorer E satellite has provided equatorial ozone mixing ratio profiles for equinox and solstice conditions. The combination of these results with a pure oxygen chemical model yields the rate of odd oxygen loss due to the sum of the odd hydrogen, nitrogen, and chlorine cycles. Use of recent mid-latitude stratospheric measurements of HO(x), NO(x), and ClO(x) with the BUV data provides an independent calculation of the catalytic loss. Below 45 km the agreement between the two sets of loss rates is satisfactory. At higher altitudes the odd hydrogen cycle provides far more O(x) loss than can be tolerated by the BUV measurements if the photodissociation of O2 is the only source and has the currently accepted magnitude. The results suggest either a tropical HO(x) concentration smaller than is now believed or the presence of a very large source of odd oxygen in the upper stratosphere and lower mesosphere.
Backscatter ultraviolet data obtained by the Explorer E satellite imply very large ozone column abundances above 56 km in the tropics during mid-day. The number of molecules in a vertical column decays by a factor of 2-3 after the solar zenith angle exceeds 75 deg in the evening. An increase of similar magnitude occurs after sunrise. Such behavior implies the presence of a greater source of odd oxygen than is included in current photochemical theories. Ozone profiles deduced between altitudes of 50 and 62 km when the solar zenith angle exceeds 80 deg are in reasonable agreement with past rocket results.
Visual airglow and low-energy electron experiment data from the Atmosphere Explorer D satellite are used to measure variations in N2(+) density and mixing in the nighttime auroral zone. The intensity of the 4278-A N2(+) emission, proportional to energy flux deposited in N2 by energetic electrons, is determined by a method which corrects for ground reflection affecting the satellite data. Calculations related to electron energy flux are found to show a slight variance from the theoretical predictions of Rees and Luckey (1974). Evidence for high-energy proton precipitation on the southern edge of the aurora and for the presence of parallel electric fields in the altitude range 150 to 800 km is also discussed.
Results of a coordinated auroral experiment involving the Atmosphere Explorer C satellite and a sounding rocket are reported. Auroral primary electron fluxes and neutral gas densities measured by instruments on the satellite are used in a model calculation of the thermospheric manifestation of the aurora. There is encouraging agreement between the calculated and measured electron density, electron temperature, secondary electron flux, and O I emissions at 5577 and 6300 A. A discrepancy between the calculated and the rocket-measured 3914-A emission profile is discussed in terms of experiment geometry and auroral physics. The coordinated measurements are used to infer vertical fluxes of ionization and of electron thermal energy at high altitudes