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NASA NTRS1980

Limits on the possible intrinsic magnetic field of Venus

Magnetic field measurements obtained by the Pioneer Venus orbiter at low altitudes in the solar wind wake region are examined for possible surface-correlated features and any possible intrinsic magnetic moment. The field variations observed in the wake do not resemble those expected for a solar wind interaction with even a weak intrinsic magnetic field. Little orbit-to-orbit persistence of features is found in the magnetic records. The magnetic field measurements in the wake are averaged in 10 deg x 10 deg bins to minimize the effects of external field sources. In these 37 bins, the average fields appear to be randomly oriented and consistent with zero mean in the region mapped. Using these 37 averaged vector fields, a maximum intrinsic magnetic dipole moment is obtained of 4.3 + or - 2.0 x 10 to the 21st G cu cm, approximately an order of magnitude less than previous estimates. It is noted that a more conservative estimate of the probable error of the mean is 5.5 x 10 to the 21st G cu cm. The Pioneer Venus measurements are thus consistent with zero planetary moment. The present measurements are found to be far below estimates made on the basis of angular momentum, the so-called magnetic Bode's law, and far below the dynamo scaling law of Busse.

Russell, C. T.↗

NASA NTRS1981

Non-equilibrium ionization in the transition region network

The consequences of the persistent downflow of material within the supergranule network of the sun are examined. An accepted temperature model and two models of velocity fields are used to determine the ion distributions of carbon, nitrogen, and oxygen throughout the transition region and to compare them with equilibrium distributions. Attention is given to how the temperature model must be modified in order to reconcile the computed line intensities with observed intensities; it is shown that a small temperature gradient, and possibly a different pressure distribution, are required. It is demonstrated that the observed downflow is probably adequate to overcome the tendency for thermal diffusion to establish concentration gradients; thus the downflow keeps the atmosphere well mixed.

Francis, M. H.↗

NASA NTRS1981

Effects of the August 1972 solar particle events on stratospheric ozone

High-energy proton data obtained by polar-orbiting satellite and several balloon flights are used to derive the spatial extent and ionization profiles of regions irradiated by the intense solar particle events (SPE) of August 1972. Backscattered ultraviolet ozone sensors on the Nimbus 4 satellite identified and tracked the polar ozone cavity created by particle ionization during the intense, ten-hour period of August 4, which persisted and rotated as a semirigid mass in an east-to-west direction during 53 days of continuous tracking. Time-dependent chemistry calculations have been performed to show the cause, magnitude, and temporal features of the ozone reduction. Attempts to verify the predicted temperature changes have been unsuccessful due to limitations in the temperature measurement techniques used.

Reagan, J. B.↗

NASA NTRS1981

The 1980 June X-ray high state of Cygnus X-1 - Optical changes

UBV photometry of Cygnus X-1 is reported from before, during, and after the 1980 June X-ray high state discovered by the Hakucho satellite. A darkening was recorded around orbital phase 0.25, also near phase 0.0, which persisted for over a month after the X-ray episode. The brightness around phase 0.75 remained normal. Light curves from preceding years are compared. Preliminary mention is also made of polarization changes during the high state.

Kemp, J. C.↗

NASA NTRS1981

Numerical simulation of the generation of electrostatic turbulence in the magnetotail

A two-dimensional plasma model is used to investigate the development of electrostatic turbulence in a magnetized plasma from plasma instabilities. The simulation consists of following the motion of 100,000 ions in their self-consistent electrostatic field. The electrons are treated as a constant neutralizing background. The instabilities modeled are driven by a ring-type velocity distribution and by interpenetrating ion beams in a time-variable magnetic field. Instability growth times are of the order of an ion gyroperiod in the case of the ring distribution and of the order of an ion plasma period in the case of the beam simulation. Maximum potential differences generated are of the order of the ion kinetic energies. These simulations demonstrate the cascade of wave energy to long wavelengths, thus showing the E x B turbulence can be generated from plasma microinstabilities. After the free energy feeding, the instabilities are exhausted, and wave energy at wavelengths less than an ion gyrodiameter decays quickly to equilibrium levels, while longer wavelength modes persist for much longer times. In one model with a time dependent, but spatially uniform, magnetic field the electric field energy at long wavelengths appeared to increase as a result of the increase of the magnetic field.

Swift, D. W.↗

NASA NTRS1981

The effect of thermal cycling to 1100 C on the alpha /Mo/ phase in directionally solidified gamma/gamma-prime-alpha alloys

Specimens of gamma/gamma-prime-alpha (Mo) eutectic alloy were thermally cycled or isothermally exposed at temperatures of 1075 to 1100 C. Transmission electron microscopy examination of cycled specimens indicated that even an exposure of 10 minutes effected noticeable changes in the shape of the alpha phase, and that the changes were cumulative as more cycles were added. The cross sections of fine, smooth fibers changed from rectangles to octagons, while lamellae and irregular shapes spheroidized. These effects are attributed to the differences in thermal expansion coefficients between the alpha phase and the gamma/gamma-prime matrix, and to the higher diffusion rates prevailing at elevated temperatures. Where the configuration of the alpha phase is a simple shape, such as a fiber, increasing the temperature eventually brings about a stress free interface between the alpha phase and the matrix by differential thermal expansion. Where the shape of the alpha phase is more complex, a stressed interface persists to higher temperatures where diffusion produces the more drastic morphological changes.

Harf, F. H.↗

NASA NTRS1981

Anomalous behavior of the atmospheric surface layer over a melting snowpack

During March, 1978 on a snow-covered field near Lee Vining, California, measurements were made that included: (1) variations above the snow surface of the net radiative flux and the profile of wind speed, air temperature and relative humidity; and (2) variations beneath the snow surface of the conductive heat flux and the temperature profile. The period was marked by clear skies, warm air and calm winds during the day, and cold air and moderate winds at night. During the day, a highly stable sublayer formed near the surface, with a persistent warm layer at approximately 0.5 m above the surface. At night, profiles agreed more with classical log-linear forms found in stable air. Numerical simulation of long and shortwave radiative fluxes near the surface, using observed humidity profiles, produced the daytime warm level in agreement with observations. It was concluded that in the absence of turbulent mixing, strong solar radiation and a supply of moisture from the snow will cause a raised maximum of temperature during the day.

Halberstam, I.↗

NASA NTRS1981

A cloud/particle model of the interstellar medium - Galactic spiral structure

A cloud/particle model for gas flow in galaxies is developed that incorporates cloud-cloud collisions and supernovae as dominant local processes. Cloud-cloud collisions are the main means of dissipation. To counter this dissipation and maintain local dispersion, supernova explosions in the medium administer radial snowplow pushes to all nearby clouds. The causal link between these processes is that cloud-cloud collisions will form stars and that these stars will rapidly become supernovae. The cloud/particle model is tested and used to investigate the gas dynamics and spiral structures in galaxies where these assumptions may be reasonable. Particular attention is given to whether large-scale galactic shock waves, which are thought to underlie the regular well-delineated spiral structure in some galaxies, form and persist in a cloud-supernova dominated interstellar medium; this question is answered in the affirmative.

Levinson, F. H.↗

NASA NTRS1981

Absorbers seen near the Venus cloud tops from Pioneer Venus

Pioneer Venus Orbiter measurements of planetary contrast at the Venus cloud tops are discussed. Images of the cloud tops at wavelengths between 1990 and 3400 A were obtained by the Pioneer UV Spectrometer together with broadband imagery and polarimetry at 2700 and 3650 A from the Orbiter Cloud Photopolarimeter at Venus phase angles of 33 to 130 deg. The planet is found to be darkest at the point where the UV Spectrometer line of sight penetrates perpendicular to the cloud tops, indicating that the absorbing material must be deep in the atmosphere. The contrast observed at wavelengths shortward of 3200 A is explained by SO2 absorption in the dark regions, while the persistence of the contrast at longer wavelengths requires the presence of an additional absorber or absorbers closely associated with the SO2, and a haze of submicron particles overlying the cloud tops in the bright regions. The correlations found between contrast and polarization indicate that no single constituent or change in vertical structure can account for the UV contrast. The origin of the markings is instead explained by a model in which absorbers subject to photochemical destruction are mixed upward into the cloud top region.

Esposito, L. W.↗

NASA NTRS1981

Plasma rest frame distributions of suprathermal ions in the earth's foreshock region

The paper presents rest frame ion distributions computed from three-dimensional observations of upstream suprathermal ions made by the University of Iowa Quadrispherical Lepedea on ISEE-1. The observations are for a single inbound midmorning pass starting upstream from the ion foreshock and continuing across the quasi-spherical bow shock into the magnetosheath. The crossing of the ion foreshock boundary is marked by a several-minute burst of ions of temperature 100-200 eV moving along the IMF away from the bow shock at 500 km/s relative to the solar wind. The observation of these reflected ions is followed by an extended interval of diffuse ions of temperatures 2-3 keV flowing at about 250 km/s relative to the solar wind and persisting until the bow shock is crossed. Both types of suprathermal ions constitute roughly 2% of the total ion density and carry a parallel heat flux of 0.01 ergs/sq cm-s.

Sentman, D. D.↗

NASA NTRS1981

Observations of solar filaments at 8, 15, 22 and 43 GHz

Radio depressions frequently appear broader than their associated H-alpha filaments and often persist after a filament disappears. The reported study is concerned with the relative contributions of filament and the filament channel to the depth of radio depressions. Although the contribution cannot readily be determined in an individual case, the apportionment can be assessed statistically by extensive multi-frequency observations of many filaments and channels using the same telescope over a period of days. In principle it is possible to determine the evolution, geometry, and physical properties of filaments and filament channels with a widely based set of radio observations. It is found that all but a few percent of the microwave depressions lie on magnetic neutral lines or their natural extensions. The only possible exceptions are coronal holes on the disk, which are small or non-existent during the period of the conducted observations. The diversity of microwave filaments is striking. Even quiescent filaments show considerable variation.

Schmahl, E. J.↗

NASA NTRS1981

On the spectrum of turbulent magnetic fields

Theoretical power spectra of magnetic fields subject to turbulent fluid motions in the kinematic regime are presented, and previous theories are reviewed, with reference to magnetic fields on the sun. Magnetic field diffusion in turbulence with persistent eddies is predicted to be described by an effective negative magnetic diffusivity. It is found that observations cannot be explained on the basis of turbulent kinematic theories unless the turbulent motions are three-dimensional, and the effective diffusivities are larger than the molecular diffusivities. Lower bounds on the turbulent viscosity are derived, suggesting that dynamical processes controlling the magnetic field spectrum occur at least 15,000 km below the surface. The results, which remain consistent with the assumption that effective diffusivity is uniform, suggest that surface magnetic field observations can be used as a diagnostic for subsurface flows.

Knobloch, E.↗

NASA NTRS1981

Annealing and anomalous high-energy electron irradiation effects in low-cost silicon N+P solar cells

Silicon solar cells of N(+)P type were subjected to 1 MeV electron irradiation (up to 10 to the 16th electrons/sq cm) and then annealed at 450 C for 20 min or annealed with no electron irradiation. Electron irradiation resulted in a degradation of longer wavelength cell response, but produced a marked enhancement of response at shorter wavelengths with a peak change of 40% at 0.44 microns. Subsequent thermal anneal at 450 C reduced the long-wavelength degradation, but enhancement at shorter wavelengths persisted. Excitation at the shorter wavelengths was in the N(+)-diffused layer and in the junction region of the cell. Anneal of unirradiated cells produced shorter-wavelength enhancement with a similar peaking at 0.44 microns, but with a relative change of only 20%. More enhancement was produced in the longer wavelength region (up to 0.8 microns). These effects in the different cell regions are explained by a decrease in the interstitial oxygen-impurity complexes (deep recombination levels) and the formation of substantial oxygen-silicon vacancy centers (donors).

Garlick, G. F. J.↗

NASA NTRS1981

Tunguska meteor fall of 1908 - Effects on stratospheric ozone

The Tunguska meteor, whose disintegration over Siberia in 1908 may have generated as much as 30 million metric tons of nitric oxide (NO) in the stratosphere and mesosphere, is discussed. The photochemical aftereffects of the event are simulated using a comprehensive model of atmospheric trace composition. Calculations are made which indicate that up to 45% of the ozone in the Northern Hemisphere may have been depleted by the meteor's nitric oxide cloud early in 1909 and that large ozone reductions may have persisted until 1912. Measurements of atmospheric transparency by the Smithsonian Astrophysical Observatory for the years 1909-1911 reveal evidence of a steady ozone recovery from unusually low levels in early 1909, implying a total ozone deficit of 30 + or - 15%. The coincidence in time between the observed ozone recovery and the Tunguska meteor fall suggests that the event may provide a test of current ozone depletion theories.

Turco, R. P.↗

NASA NTRS1981

Rotation of dwarf star chromospheres in the ultraviolet

Periodic variations in the ultraviolet fluxes of chromospheric emission line multiplets are investigated for F, G and K stars as evidence of rotational modulation. Vacuum ultraviolet spectra were obtained with the IUE spacecraft for six stars as many as 11 times over the period April 23 to December 3, 1980. Variations in the emission fluxes of the hydrogen Lyman-alpha, Si II and Mg II lines are observed with periods up to 47 days. The periodicity, which is identified with rotational modulation, is found to persist over many rotational cycles, although the periods and time dependences of the fluxes from the different ionic species are not identical, probably due to differential rotation and global distributions. The spread of the UV periods is observed to be within 10%, with one or two peaks per cycle and a ratio of modulated to umodulated flux ranging from 1.1 to 3.0, analogous to solar behavior.

Hallam, K. L.↗

NASA NTRS1981

Reynolds number effects in combustion noise

Acoustic emission spectra have been obtained for non-premixed turbulent combustion from two small diameter laboratory gas burners, two commercial gas burners and a large gas burner in the firebox of a Babcock-Wilcox Boiler (50,000 lb steam/hr). The changes in burner size and firing rate represent changes in Reynolds number and changes in air/fuel ratio represent departure from stoichiometric proportions. The combustion efficiency was measured independently through gas analysis. The acoustic spectra obtained from the various burners exhibit a persistent shape over the Reynolds number range of 8200-82,000. The spectra were analyzed for identification of a predictable frequency domain that is most responsive to, and readily correlated with, combustion efficiency. A simple parameter (consisting of the ratio of the average acoustic power output in the most responsive frequency bandwidth to the acoustic power level of the loudest frequency) is proposed whose value increases significantly and unmistakably as combustion efficiency approaches 100%. The dependence of the most responsive frequency domain on the various Reynolds numbers associated with turbulent jets is discussed.

Seshan, P. K.↗

NASA NTRS1981

Magnetic clouds between 2-4 AU: Voyager observations

Magnetic clouds were observed in the solar wind between 2-4 AU. It was shown that they are stable enough to persist without major changes out to such distances. It is estimated that the clouds expand at a speed of the order of 45 km/s. The average Alfven speed at the front and rear boundaries is 104 km/s, the expansion speed is estimated to be nearly half of the Alfven speed, which is consistent with an earlier estimate of the expansion speed of clouds between the Sun and 1 AU. The magnetic field configuration is highly ordered and consistent with the passage of some kind of loop.

Burlaga, L. F.↗

NASA NTRS1981

Compensation for use of monthly-averaged winds in numerical modeling

Ratios R of the monthly averaged wind speeds to the magnitudes of the monthly averaged wind vectors are presented over a 41 x 41 grid covering the southern Ocean and the Antarctic continent. The ratio is found to vary from 1 to over 1000, with an average value of 1.86. These ratios R are relevant for converting from sensible and latent heats calculated with mean monthly data to those calculated with 12 hourly data. The corresponding ratios alpha for wind stress, along with the angle deviations involved, are also presented over the same 41 x 41 grid. The values of alpha generally exceed those for R and average 2.66. Regions in zones of variable wind directions have larger R and alpha ratios, over the ice-covered portions of the southern Ocean averaging 2.74 and 4.35 for R and alpha respectively. Thus adjustments to compensate for the use of mean monthly wind velocities should be stronger for wind stress than for turbulent heats and stronger over ice covered regions than over regions with more persistent wind directions, e.g., those in the belt of mid-latitude westerlies.

Parkinson, C. L.↗