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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 631 records · Page 35
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NASA NTRS1979

Short-term cyclic variations and diurnal variations of the Venus upper atmosphere

The vertical structure of the nighttime thermosphere and exosphere of Venus was discussed. A comparison of the day and nighttime profiles indicates, contrary to the model of Dickinson and Riley (1977), that densities (principally atomic oxygen) dropped sharply from day to night. It was suggested either that the lower estimates were related to cooler exospheric temperatures at night or that the atomic bulge was flatter than expected at lower altitudes. Large periodic oscillations, in both density and inferred exospheric temperatures, were detected with periods of 5 to 6 days. The possibility that cyclic variations in the thermosphere and stratosphere were caused by planetary-scale waves, propagated upward from the lower atmosphere, was investigated using simultaneous temperature measurements obtained by the Venus radiometric temperature experiment (VORTEX). Inferred exospheric temperatures in the morning were found to be lower than in the evening as if the atmosphere rotated in the direction of the planet's rotation, similar to that of earth. Superrotation of the thermosphere and exosphere was discussed as a possible extension of the 4-day cyclic atmospheric rotation near the cloud tops.

Keating, G. M.↗
NASA NTRS1979

On the structure of the upper atmosphere of Mars according to data from experiments on the Viking space vehicles

Altitude profiles of the concentrations of the atmospheric components measured by the on board mass spectrometers during the descent of Viking lander are discussed by assuming that temperature has a smoother profile, and the eddy mixing coefficients are smaller at altitudes of 120 to 170 km than those formally determined. The influence of acoustic gravitational waves and errors in measurements and calculations are discussed in relation to the convolutions in the altitude profiles of the concentrations of the atmospheric components and the temperature of the atmosphere.

Izakov, M. N.↗
NASA NTRS1979

Jovian upper atmospheric temperature measurement by the Voyager 1 UV spectrometer

A measurement of the neutral temperature in the exosphere of Jupiter is reported. The observations were carried out by the Voyager 1 Ultraviolet Spectrometer during the solar occultation phase beginning 4.5 hours after the Jupiter encounter. The range of the exospheric temperature is found to be 1450 (+300, -250) K. The uncertainty in the determination of the temperature appears to be largely a consequence of the lack of knowledge of the brightness distribution on the solar disk at the time of the observations. The high exospheric temperature appears to result from a combination of upward-propagating inertia gravity waves, magnetospheric soft electrons, and auroral electrons, including those from the Io-plasma torus.

Atreya, S. K.↗
NASA NTRS1979

Density models for the upper atmosphere

Three contemporary atmospheric density models which are candidates for meeting the current orbit computation requirements are compared. The models considered are the analytic Jacchia-Roberts model, the modified Harris-Priester model, and the USSR Cosmos satellite derived density model. All of these models can be said to be quasi-dynamic representations of the atmospheric density. The time dependent variations in the model density profiles are determined by both the evaluation of explicit continuous functions of time and by the input of time varying parameters to algorithms. The computation characteristics of each of the models are compared and a modification to the modified Harris-Priester model is proposed which improves its ability to represent the diurnal variation in the atmospheric density.

Dowd, D. L.↗
NASA NTRS1980

The upper atmosphere of Uranus - Mean temperature and temperature variations

The number-density, pressure, and temperature profiles of the Uranian atmosphere in the pressure interval from 0.3 to 30 dynes/sq cm are derived from observations of the occultation of SAO 158687 by Uranus on 1977 March 10, observations made from the Kuiper Airborne Observatory and the Cape Town station of the South African Astronomical Observatory. The mean temperature is found to be about 95 K, but peak-to-peak variations from 10 K to 20 K or more exist on a scale of 150 km or 3 scale heights. The existence of a thermal inversion is established, but the inversion is much weaker than the analogous inversion on Neptune. The mean temperature can be explained by solar heating in the 3.3 micron methane band with a methane mixing ratio of 4 x 10 to the -6th combined with the cooling effect of ethane with a mixing ratio of not greater than 4 x 10 to the -6th. The temperature variations are probably due to a photochemical process that has formed a Chapman layer.

Dunham, E.↗
NASA NTRS1980

Early harvest: The upper atmosphere and cosmic rays

Achievements in space science through 1958 are summarized. Topics discussed are: the scheduling of V-2 flights; the development of newer rockets; the testing of spaceborne instruments; the seeking of financial support for space research; and the problems of international cooperation. Special emphasis is placed on atmospheric sounding.

Source record↗
NASA NTRS1980

Recent assessment of the performance and accuracy of a chemiluminescent rocket sonde for upper atmospheric ozone measurements

The chemiluminescent rocket ozonesonde utilizing rhodamine-B as a detector and self-pumping for air sampling has been improved. The instrument employs standard meteorological sounding systems and is the only technique available for routine nighttime ozone measurements above balloon altitudes. The chemiluminescent detector, when properly calibrated, is shown to be specific to ozone, stable, and of sufficient sensitivity for accurate measurements of ozone from about 65-20 km. An error analysis indicates that the measured ozone profiles have an absolute accuracy of about + or - 12% and a precision of about + or - 6%. Approximately 20 flights have been conducted for geophysical investigations, while additional flights were conducted with other rocket and satellite ozone soundings for comparisons. In general, these comparisons showed good agreement.

Hilsenrath, E.↗
NASA NTRS1980

The morphology of metallic ions in the upper atmosphere

Analysis of metallic ion data from a day-night pair of rockets, OGO 6, and the elliptic phases of AE-C and AE-D shows the presence of Fe(+) ions at altitudes above 400 km only at low magnetic latitudes. The detection probability of this ion decreases with altitude, with a maximum over the Atlantic and a minimum over India; the rocket data indicate ions in the E region during the day and on the bottom of the F layer at night. Mg(+) and Fe(+) are the dominant ions below 250 km at all latitudes, but Al(+), Na(+), Si(+), and Ca(+) are also detectable; a correlation was found between solar activity and metallic ion detection probability at low latitudes and high altitudes at night

Kumar, S.↗
NASA NTRS1981

Hot oxygen atoms in the upper atmosphere of Venus

Using data obtained by an ultraviolet spectrometer on the Pioneer-Venus Orbiter, energy and altitude distribution of nonthermal oxygen atoms in the Venus atmosphere for typical daytime and nighttime conditions are calculated using two different numerical methods. Agreement is found between results obtained by the two-stream transport method and the diffusion equation technique. Dissociative recombination of molecular oxygen ions and charge exchange of atomic oxygen ions with the neutral hydrogen and oxygen gas are the source terms, and calculations show that the dissociative recombination term is the dominant one. It is shown that measured hot atom concentrations exceed estimates of the thermal hydrogen atom concentrations derived from Brinton et al. (1980) over most of the daytime exosphere, and the calculated concentrations do so to an even greater extent. It is concluded that hot oxygen atoms are an important component of the dayside exosphere of Venus, their most important effect being the absorption of solar wind.

Nagy, A. F.↗
NASA NTRS1981

Application of microprocessors in an upper atmosphere instrument package

A servo-driven magnetometer table measuring offset from magnetic north has been developed by NASA to calculate payload azimuth required to point at a celestial target. Used as an aid to the study of gamma-ray phenomena, the high-altitude balloon-borne instrument determines a geocentric reference system, and calculates a set of pointing directions with respect to the system. Principal components include the magnetometer, stepping motor, microcomputer, and gray code shaft encoder. The single-chip microcomputer is used to control the orientation of the system, and consists of a central processing unit, program memory, data memory and input/output ports. Principal advantages include a low power requirement, consuming 6 watts, as compared to 30 watts consumed by the previous system.

Lim, T. S.↗
NASA NTRS1982

The transport of nitric oxide in the upper atmosphere by planetary waves and the zonal mean circulation

A time-dependent numerical model was developed and used to study the interaction between planetary waves, the zonal mean circulation, and the trace constituent nitric oxide in the region between 55 km and 120 km. The factors which contribute to the structure of the nitric oxide distribution were examined, and the sensitivity of the distribution to changes in planetary wave amplitude was investigated. Wave-induced changes in the mean nitric oxide concentration were examined as a possible mechanism for the observed winter anomaly. Results indicate that vertically-propagating planetary waves induce a wave-like structure in the nitric oxide distribution and that at certain levels, transports of nitric oxide by planetary waves could significantly affect the mean nitric oxide distribution. The magnitude and direction of these transports at a given level was found to depend not only on the amplitude of the planetary wave, but also on the loss rate of nitric oxide at that level.

Jones, G. A.↗
NASA NTRS1982

Titan's upper atmosphere - Composition and temperature from the EUV solar occultation results

It is inferred from observation of an occultation of the sun by Titan, using the Voyager 1 UV spectrometer, that temperatures are 176 + or - 20 K near the evening terminator and 196 + or - 20 K near the morning terminator, and that the major atmospheric constituent is N2, with a density of 2.7 + or - 0.2 x 10 to the 8th/cu cm at 3840 km. A layer of absorbing molecules, possibly polymers, is found near both morning and evening terminators. A photochemical model suggests that the homopause is located at 3500 + or - 70 km, with an eddy diffusion coefficient of 1(+2, -0.7) x 10 to the 8th/sq cm per sec, which decreases to about 1000 sq cm/sec in the lower stratosphere as N2 to the -2/3 power.

Smith, G. R.↗
NASA NTRS1982

Voyager ultraviolet stellar occultation measurements of the composition and thermal profiles of the Saturnian upper atmosphere

Occultation of the star Delta-Scorpii by Saturn as recorded by the Voyager Ultraviolet Spectrometer yields the value of the exospheric temperature in the equatorial region to be 800 (+150, -120) K at an altitude of 1540 km above the 1-bar atmospheric pressure level; the H2-density at 1540 km is determined to be 5 (+3.6, -1.8) x 10 to the 9th per cu cm. Temperature gradient in the thermosphere is found to be 1.25 (+0.05, -0.07) K/km. Methane volume mixing ratio at 965 km above the 1-bar pressure level is determined to be 0.00015.

Festou, M. C.↗
NASA NTRS1982

Jacchia-Lineberry upper atmosphere density model

A series of increasingly accurate models which are a careful blend of empirical and theoretical formulae were developed. The exospheric temperature is assumed to be a function of: (1) the average and daily variations in the solar flux, (2) the average and three hourly variations in the geomagnetic index, (3) the angle between the position vector and the axis of the unsymmetric atmospheric bulge, and (4) the angle between the position vector and the geomagnetic pole. The exospheric temperature is related to the density by the solution of the diffusion equilibrium equations for the different constituents of the atmosphere as a function of altitude. Other variations are modeled directly as changes in the density. They are: (1) changes due to the semiannual effect, and (2) changes due to the seasonal latitudinal effect. The causes for these variations are not exactly known but may be modeled sufficiently by empirical formulae. The Jacchia model is assumed to be valid over the altitude range of 90 to 2500 km. The residuals between the observed density from satellite drag observations and the computed densities show the mean relative error to be generally less than 10 percent with occasional peak errors near 50 percent.

Mueller, A. C.↗
NASA NTRS1982

The upper atmosphere of Uranus - A critical test of isotropic turbulence models

Observations of the August 15, 1980, Uranus occultation of KM 12, obtained from Cerro Tololo InterAmerican Observatory, European Southern Observatory, and Cerro Las Campanas Observatory, are used to compare the atmospheric structure at points separated by approximately 140 km along the planetary limb. The results reveal striking, but by no means perfect correlation of the light curves, ruling out isotropic turbulence as the cause of the light curve spikes. The atmosphere is strongly layered, and any acceptable turbulence model must accommodate the axial ratios of greater than about 60 which are observed. The mean temperature of the atmosphere is 150 plus or minus 15 K for the region near number density 10 to the 14th per cu cm. Derived temperature variations of vertical scale approximately 130 km and amplitude plus or minus 5 K are in agreement for all stations, and correlated spikes correspond to low-amplitude temperature variations with a vertical scale of several kilometers.

French, R. G.↗
NASA NTRS1983

Vertical distribution of scattering hazes in Titan's upper atmosphere

Radial intensity scans of a Voyager 2 high phase angle image of Titan have been inverted to yield vertical extinction profiles at 1 deg intervals around the limb. A detached haze layer with peak particle number densities of about 0.2 cu/cm exists at all latitudes south of about 45 N, and at an altitude of 300-350 km. The optical depth 0.01 level lies at a radius of 2932 + or - 5 km at the equator and at a radius of 2915 + or - 10 km over the poles (altitudes of 357 + or - 5 and 340 + or - 10 km, respectively). In addition to the haze layer at 300-350 km, there is a small enhancement in the extinction at about 450 km which exists at all latitudes between 75 deg S and about 60 deg N.

Rages, K.↗