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At least 163 records · Page 9
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NASA NTRS1977

The brightness temperatures of Saturn and its rings at 39 microns

The relative rings-to-disk brightness (specific intensity) of Saturn at 39 microns was resolved using a 224-cm telescope, and the total flux of Saturn relative to Jupiter in the same bandpass was measured from the NASA Learjet Observatory. These two measurements, which were made with Saturn's rings near maximum inclination, determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it impossible to compare existing measurements unambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 microns are all compatible (within 2 sigmas) with a disk brightness temperature of 94 K and do not agree with the radiative equilibrium models of Trafton (1967); (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for wavelengths not exceeding about 40 microns; and (3) there is a decrease of approximately 22% in the relative ring:disk brightness between effective wavelengths of 33.5 and 39 microns.

Nolt, I. G.↗
NASA NTRS1977

Photochemistry of tropospheric ozone

A photochemical equilibrium model of minor constituent chemistry in the troposphere was constructed to investigate the photochemistry of tropospheric ozone. We find that photochemical production must be supplemented by additional sources to account for observed ozone levels in clean air, while photochemical loss is more important than surface destruction as an ozone loss mechanism. Photochemically produced ozone is sensitive to the NO(x) background in the model, exhibiting a maximum of about 0.5 ppb of NO(x).

Stewart, R. W.↗
NASA NTRS1978

Line formation in the solar chromosphere. I - The C II resonance lines observed with OSO 8

The temperature structure of the upper chromosphere is investigated using center-to-limb measurements of the C II resonance lines at 1335 A from the University of Colorado spectrometer aboard OSO 8. Spectrum synthesis of these lines shows them to be extremely sensitive to the temperature and the physical extent of the 20,000 K plateau proposed by Vernazza et al (1973). Hydrostatic equilibrium models of the quiet chromosphere are computed to obtain theoretical spectra of the Lyman lines and continuum as well as the center-to-limb behavior of the C II lines. Good agreement is found with observations for a plateau at 16,500 K with about 25% more material than that of Vernazza et al.

Lites, B. W.↗
NASA NTRS1979

X-ray evidence for electron-ion equilibrium and ionization nonequilibrium in young supernova remnants

The A-2 spectroscopy experiment on HEAO 1 detected X-ray emission up to 25 keV from the supernova remnants Cas A and Tycho. The spectra must include continuum components with effective temperature equivalent or 10 to the 8th power K which could arise from optically thin plasmas in the collisionless shock fronts. This is the first indication of electron-ion temperature equilibrium in the expanding shell of young remnants. Measurements of the equivalent widths of the K alpha and K beta iron line blends in Cas A, show that their ratio is not compatible with the measured X-ray temperature in the collisional ionization equilibrium model. The search for hard X-ray pulsars in both remnants was unsuccessful.

Pravdo, S. H.↗
NASA NTRS1978

Tropospheric ozone

Photochemical equilibrium models have been used to study the effect of recent revisions in important chemical reaction rates on the calculated tropospheric ozone concentration. Reasonable agreement with observed values is obtained if the NO(x) background is approximately 0.02 to 0.03 ppb, about an order of magnitude less than used in many previous model studies, but consistent with present nitrogen budget considerations and with observations of NO2. Chemical production and loss of ozone may dominate transport terms depending on values of key chemical rate constants and of the NO(x) background. This is consistent with the structure observed in the mean annual latitudinal distribution of ozone since ozone is its own chemical precursor and regions of enhanced stratosphere-troposphere exchange are also regions of enhanced photochemical activity.

Stewart, R. W.↗
NASA NTRS1979

Atmospheric lapse rate regimes and their parameterization

Lapse rates, moist adiabatic lapse rates and the critical lapse rate for baroclinic adjustment are calculated and compared for the mean annual, January and July states in the Northern Hemisphere. The small seasonal changes in hemispheric mean lapse rates can be attributed to counteracting seasonal changes in the strength of moist convection and baroclinic eddies. A major conclusion is that the vertical temperature structure may be well approximated by a radiative-convective equilibrium model with two critical lapse rates, viz. the moist adiabatic lapse rate and the critical lapse rate for baroclinic adjustment.

Stone, P. H.↗
NASA NTRS1979

A cluster ion chemistry for the mesospheric sodium layer

A cluster ion chemistry for sodium is developed which relates the Na(+) profile to the Na profile using reactions involving Na(+).N2, Na(+).CO2, and Na(+).H2O. Removal of sodium from the mesosphere is accomplished by the formation of higher order clusters of the form Na(+).(H2O)n which presumably precipitate to the lower atmosphere. This sink is most effective in the 80-85 km altitude range. The chemical equilibrium model is applied to experimental observations of the Na and Na(+) layers.

Richter, E. S.↗
NASA NTRS1980

X-ray observations of Algol

Observations of Algol using a solid state spectrometer onboard the Einstein Observatory are discussed. Two observations six months apart were made, both during a primary optical eclipse. No corresponding X-ray eclipses were seen. During the second observation the source was flaring and was on average a factor three brighter. The spectrum on both occasions was consistent with a two-component thermal equilibrium model with temperatures of approximately 7.5 and 40 million degrees. Attempts to insert a third component indicate the temperature distribution to be bimodal. Models for the X-ray emission are discussed and it is suggested that the emission most likely originates from an active corona surrounding the K star.

White, N. E.↗
NASA NTRS1979

X-ray evidence for electron-ion equilibrium and ionization nonequilibrium in Young supernova remnants

X-ray emission up to 25 keV from the supernova remnants Cas A and Tycho has been detected with the A-2 spectroscopy experiment on HEAO 1. The spectra must include continuum components with effective temperature of about 10 to the 8th K which could arise from optically thin plasmas in the collisionless shock fronts. This is the first indication of electron-ion temperature equilibrium in the expanding shell of young remnants. The equivalent widths of the K-alpha and K-beta iron line blends in Cas A have also been measured and it is found that their ratio is not compatible with the measured X-ray temperature in the collisional ionization equilibrium model. Finally, an unsuccessful search has been conducted for hard X-ray pulsars in both remnants.

Pravdo, S. H.↗
NASA NTRS1980

Spectrophotometry of Comet West

Postperihelion observations of Comet West (1975n = 1976 VI) have been made with a Fourier transform spectrometer at heliocentric distances from 0.57 to 1.68 AU. Measurements were made of the emission bands of C2, CN, C3, CH, and NH2, as well as the emission lines of Na D and forbidden (O I), and the flux in the continuum in nine different bandpasses. Several ratios of the band strengths of CN have been used to determine the two free parameters in the fluorescence equilibrium model of CN of Danks and Arpigny (1973). From the values of the parameters it is inferred that the vibrational transition probability for the ground electronic state is between 0.025 and 0.075 per sec and that the ratio of oscillator strengths between the (0-0) bands of the violet and red systems is between 25 and 30. When corrected for field-of-view effects, NH2 shows no systematic variation in abundance relative to C2 while CH shows a small increase. The cometary continuum is found to be slightly redder than the solar continuum, consistent with results for other bright, dusty comets. The equivalent width of the Delta u = 0 sequence of C2 shows a marked decrease at r(H) = 1.2 AU.

Ahearn, M. F.↗
NASA NTRS1980

X-ray observations of Algol

The Solid State Spectrometer on Einstein has been used to study Algol. Two observations six months apart were made, both including a primary optical eclipse. No corresponding X-ray eclipses were seen. During the second observation the source was flaring and was on the average a factor of three brighter. The spectrum on both occasions was consistent with a two-component thermal equilibrium model with temperatures of approximately 7.5 and 40 million degrees. Attempts to insert a third component indicate the temperature distribution to be bimodal. Models for the X-ray emission are discussed and it is suggested that it most likely originates from an active corona surrounding the K star.

White, N. E.↗
NASA NTRS1980

The latitudinal variation of the charge exchange induced atomic hydrogen escape flux

Using plasma data from the Isis 2 spacecraft and Arecibo radar, diffusive equilibrium models of the ionosphere were constructed for equinox conditions. These plasmaspheric models were combined with models of the neutral atmosphere to calculate the atomic hydrogen escape flux due to charge exchange between thermal protons and to calculate cooler hydrogen and oxygen atoms as a function of dipole latitude and local time. These calculations showed that the daytime escape flux increases as the absolute value of the dipole latitude decreases, reaching its maximum value at the magnetic equator. At 15 hours local time (LT) on March 23, 1972, the calculated escape flux varied from an insignificant amount at 55 deg dipole latitude, to 3 x 10 to the 8th atoms/sq cm sec at the magnetic equators.

Maher, L. J., Jr.↗
NASA NTRS1980

Dielectronic recombination rates, ionization equilibrium, and radiative emission rates for calcium and nickel ions in low-density high-temperature plasmas

The total dielectronic recombination rates for Ca and Ni ions were calculated taking into account autoionization to excited states of the recombining ion and stabilizing radiative transitions of the recombining electron. Radiative transitions of the recombining ion are found to be the dominant stabilizing processes, and the relative importance of Delta n = 0 and Delta n not equal to 0 transitions in the relevant temperature region is determined for each ion. The relative importance of the Delta n = 0 and Delta n not equal to 0 contributions is significantly altered for some ions by the inclusion of autoionization to excited levels. The relative abundance of the various ionization stages has been determined by using a corona equilibrium model in which collisional ionization and inner-shell excitation followed by autoionization are balanced by direct radiative and dielectronic recombination.

Jacobs, V. L.↗
NASA NTRS1982

Thermal Structure of Jupiter and Saturn

Temperatures in the sensible regions of the atmospheres of the outer planets are quite cold. The temperature structures for Jupiter, Saturn, Uranus and Neptune, derived from the equilibrium models are presented in preparation. The vertical temperature profiles for Jupiter and Saturn, the molecular spectroscopic data which form the basis for this type of analysis, and the problems involved with these models for molecular absorption and with the recovery technique in general, are discussed. Results for Jupiter and Saturn from the Pioneer and Voyager infrared experiments are also presented.

Orton, G.↗
NASA NTRS1981

A comparison of equatorial electron densities measured by whistlers and by a satellite radio technique

Magnetospheric equatorial electron densities determined from whistler observations are compared with in situ satellite measurements of electron density along near-equatorial orbits. Whistler data was recorded at Siple and Palmer, Antarctica, while the sweep frequency receiver on ISEE-1 was used to measure plasma densities during passes within about 15 deg of the whistler station longitudes at L values between 3 and 5.2. The whistler and satellite data sets are found to be in good agreement for the three rendezvous considered, suggesting that the diffusive equilibrium model applied to calculate electron densities from whistler measurements was appropriate for the description of electron density distributions along field lines in the outer plasmasphere. Data also indicate that density enhancements within the whistler ducts were not more than about 30% of the mean or interduct level, and that there were no significant east-west density gradients within about 15 deg of whistler station longitudes over the L range of the study.

Carpenter, D. L.↗
NASA NTRS1981

Stratospheric eddy diffusion coefficients from tracer data

Global distributions of nitrous oxide, methane, ozone, and carbon 14 are used to estimate four sets of stratospheric eddy diffusion coefficients. A photochemical equilibrium model calculates O(3P), O(1D), H, HO2, OH, H2O2, NO, and NO2 densities, as a function of altitude, latitude, and time. The calculated O(1D), OH, and observed Cl densities are used to obtain the eddy profiles associated with the methane and nitrous oxide distributions, for altitudes between 10 and 40 km. Application of a constant flux condition to the seasonally averaged ozone data yields eddy values below 20 km. Time-dependent carbon 14 calculations produce eddy coefficients between 13 and 27 km. A composite profile is obtained by comparing the four sets of coefficients. Further, carbon 14 computations are used to test these profiles as well as those recommended in reports issued by the National Academy of Sciences in 1976 and 1979. The composite eddy profile produces the best agreement.

Massie, S. T.↗
NASA NTRS1982

Plasmaspheric helium ion distribution from satellite observations of He II 304-A

High sensitivity and spatial resolution observations of the He II 304-A emission line intensity in the earth's nightglow have been carried out by the extreme ultraviolet telescope on the Apollo-Soyuz mission in July, 1975. The data, obtained over a wide range of plasmasphere parameters, are compared to the predictions of a kinetic equilibrium model of plasmaspheric ion density. Excellent agreement between observation and theory is found using as inputs a temperature model, solar flux and H(+) and O(+) number densities determined by extrapolating nearly simultaneous Atmospheric Explorer C measurements at 300 km. The observations in the Northern Hemisphere are well fit by a model having 285 He(+) ions/cu cm at 500 km independent of latitude or longitude, while those in the south require 430 He(+) ions/cu cm at the same altitude. This result is consistent with available information on the interhemispheric asymmetry of He(+) observed by a mass spectrometer on Explorer 32 and on the winter neutral helium bulge.

Chakrabarti, S.↗
NASA NTRS1982

Effective temperatures of A and F stars

Effective temperatures of late A and early F stars are determined from the observed fluxes in the visual at 1900 A and 1420 A. The observed ratios are compared with those calculated by Kurucz (1979). A correction of the theoretical fluxes at 1900 A brings the effective temperatures obtained from different ratios into reasonable agreement. The effective temperatures determined in this way for late A stars agree well with those obtained from the optical region. For F stars, however, the effective temperatures obtained from the UV are found to be higher than those obtained from the optical region if radiative equilibrium models are used for the comparison. It is thought that this discrepancy may derive from the effects of temperature, pressure, and absorption coefficient inhomogeneities caused by convection.

Boehm-Vitense, E.↗