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At least 667 records · Page 37

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NASA NTRS1976

Optical and physical requirements for fluid particles marking trailing vortices from aircraft

A theoretical study of the optical and physical requirements of marking trailing vortices that emanate from aircraft wings was carried out by considering particulate light-scattering properties, ability of particles to follow trailing vortices, and survival time of particles to vortex dissipation. Liquid droplets undergoing evaporation and molecular dispersion were investigated. Droplets should have lifetimes of about 300 sec. Droplet size should be about 1 micron to maximize light scattering with the minimum mass of liquid required. Droplets of this small size would spiral outward very slowly and essentially remain in the vortex cores. Nontoxic hygroscopic liquids, having an affinity for moisture in the air, have been identified. These liquids have relatively low vapor pressures of order 10 to the -5 mm Hg that would insure droplet persistence long enough to mark trailing vortices.

Back, L. H.↗

NASA NTRS1976

Satellite observation of the mesospheric scattering layer and implied climatic consequences

Recent satellite photometry of the airglow has detected an extensive, though tenous, scattering layer above the summer polar cap. Located near the mesopause, the layer persists throughout the summer season poleward of about 75 deg latitude. By employing a simple growth model for the layer a time dependent radiative transfer model has been developed to examine radiative temperature perturbations. As was anticipated, the global temperature perturbations are negligible. However, in the polar region the impact is probably nonnegligible, the temperature decrease being of the order of a few tenths of a degree. The climatological implications of the layer on the polar region are discussed.

Hummel, J. R.↗

NASA NTRS1976

Possible radio emission from Uranus at 0.5 MHz

Radio emission from the direction of Uranus has been detected in data from the Goddard radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn had been observed by IMP-6 at a number of frequencies near 1 MHz and were identified through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics have been found. The events persisted less than 3 minutes and are strongest in intensity near 0.5 MHz. Identification with Uranus is confused by the likely presence of low-level terrestrial and solar emission. Because of the unfavorable angular separation of earth and Uranus, there is a possibility that the bursts are atypical terrestrial magnetospheric phenomena, although the uniqueness of the set of events indicates the probable detection of radiation from Uranus.

Brown, L. W.↗

NASA NTRS1976

Evidence for a Rayleigh-Taylor type instability and upwelling of depleted density regions during equatorial spread F

Recent rocket probe, barium cloud and radar measurements conducted during equatorial spread F conditions are interpreted in terms of a Rayleigh-Taylor gravitational instability operating on the bottomside of the F peak. The persistent theoretical problems associated with strong radar echoes typically observed in patch-like structures at high altitudes are explained in terms of regions of depleted plasma density which buoyantly rise against the gravitational field.

Kelley, M. C.↗

NASA NTRS1976

Bow shock and magnetosheath waves at Mercury

Mariner 10 measurements at the Mercury bow shock provide examples where the magnetic field is approximately parallel or perpendicular to the bow shock normal. Upstream of a broad irregular parallel shock, left-hand circularly polarized waves are observed which cut off very sharply at about 4 Hz. Upstream of a perpendicular shock, righ-hand circularly polarized waves are observed which persist up to the Nyquist frequency of 12 Hz. Determination of the wave propagation vector as a function of frequency helps to identify conclusively the waves as whistler mode waves propagating from the shock. The magnetosheath downstream of the parallel shock is disturbed more than that downstream of the perpendicular shock, particularly below 1 Hz. In the latter case, regular left-hand-polarized waves observed slightly above the proton gyrofrequency are identified as ion cyclotron waves with wavelengths of about 300 km which have been Doppler shifted up to their observed frequency.

Fairfield, D. H.↗

NASA NTRS1976

Simultaneous observation of whistlers at two L about 4 Alaskan stations

Results are presented for simultaneous observations of whistlers at two Alaskan stations (L roughly 4) during one occasion lasting 24 hr, another lasting 10 hr, and a third lasting 6 hr. Of the three periods of simultaneous observations studied, two showed patterns of equatorial electron density which were stationary in L-LMT space and which were unchanging for at least 1.5 hr of UT. The third showed a marked change, the nature of which being accounted for by east-west gradients corotating with the stations. All three periods exhibited persistent stationary patterns of whistler duct tracks, each thin in the cross-L direction and extensive in the east-west direction. It would appear that either the ducts are stable shells or there is a succession of ducts arrayed along the contours and possibly corotating with the earth along the stationary tracks. Multistation direction finding on the whistler exit points may elucidate the relevant interpretations.

Morgan, M. G.↗

NASA NTRS1976

The morphology and origin of Hadley Rille, the moon

Hadley Rille is directly related to the emplacement of mare basalts in Palus Putredinis. Existing hypotheses of sinuous rille origin are in discord with the cooling behavior of deep lava flows and the strength of materials. It is proposed that Hadley Rille is a channel which returned lava to the southern vent from which it initially extruded and that the channel persisted through many episodes of volcanism. This view is supported by available topographic information obtained by the lunar orbiter photography and the Apollo 15 mission.

Brewer, T.↗

NASA NTRS1976

An advanced concept that promises ecological and economic viability

The actuality of supersonic commercial service being provided by Concorde is demonstrating to the world the advantages offered by supersonic travel for both business and recreation. Public acceptance will gradually and persistently stimulate interest to proceed with a second generation design that meets updated economic and ecological standards. It is estimated that this concept could operate profitably on world-wide routes with a revenue structure based upon economy fares. Airplanes will meet all present day ecological requirements regarding noise and emissions.

Wright, B. R.↗

NASA NTRS1977

The effects of the laminar/turbulent boundary layer states on the development of a plane mixing layer

The effect of the laminar/turbulent boundary layer state on the mean and rms velocities of a developing plane mixing layer was investigated. The use of commonly accepted nondimensional representations of the data confirm (at least) an approximately self-preserving condition. It is suggested that the effects of the laminar/turbulent initial condition persist in the self-preserving region.

Foss, J. F.↗

NASA NTRS1977

Global plate tectonics and the secular motion of the pole

Astronomical data compiled during the last 70 years by the international organizations providing the coordinates of the instantaneous pole clearly shows a persistent drift of the mean pole. The differential contributions to the earth's second-order tensor of inertia were obtained and applied, resulting in no significant displacement of the earth's principal axis. In view of the above, the effect that theoretical geophysical models for absolute plate velocities may have on an apparent displacement of the mean pole as a consequence of station drifting was analyzed. The investigation also reports new values for the crustal tensor of inertia (assuming an ellipsoidal earth) and the orientation of its axis of figure, reopening the old speculation of a possible sliding of the whole crustover the upper mantle, including the supporting geophysical and astronomic evidence.

Soler, T.↗

NASA NTRS1977

The determination of surface albedo from meteorological satellites

A surface albedo was determined from visible data collected by the NOAA-4 polar orbiting meteorological satellite. To filter out the major cause of atmospheric reflectivity, namely clouds, techniques were developed and applied to the data resulting in a map of global surface albedo. Neglecting spurious surface albedos for regions with persistent cloud cover, sun glint effects, insufficient reflected light and, at this time, some unresolved influences, the surface albedos retrieved from satellite data closely matched those of a global surface albedo map produced from surface and aircraft measurements and from characteristic albedos for land type and land use.

Johnson, W. T.↗

NASA NTRS1977

Early impact basins and the onset of plate tectonics

The fundamental crustal dichotomy of the Earth (high and low density crust) was established nearly 4 billion years ago. Therefore, subductable crust was concentrated at the surface of the Earth very early in its history, making possible an early onset for plate tectonics. Simple thermal history calculations spanning 1 billion years show that the basin forming impact thins the lithosphere by at least 25%, and increases the sublithosphere thermal gradients by roughly 20%. The corresponding increase in convective heat transport, combined with the highly fractured nature of the thinned basin lithosphere, suggest that lithospheric breakup or rifting occurred shortly after the formation of the basins. Conditions appropriate for early rifting persisted from some 100,000,000 years following impact. We suggest a very early stage of high temperature, fast spreading "microplate" tectonics, originating before 3.5 billion years ago, and gradually stabilizing over the Archaean into more modern large plate or Wilson Cycle tectonics.

Frey, H.↗

NASA NTRS1977

Optimum space shuttle launch times relative to natural environment

Three sets of meteorological criteria were analyzed to determine the probabilities of favorable launch and landing conditions. Probabilities were computed for every 3 hours on a yearly basis using 14 years of weather data. These temporal probability distributions, applicable to the three sets of weather criteria encompassing benign, moderate and severe weather conditions, were computed for both Kennedy Space Center (KSC) and Edwards Air Force Base. In addition, conditional probabilities were computed for unfavorable weather conditions occurring after a delay which may or may not be due to weather conditions. Also, for KSC, the probabilities of favorable landing conditions at various times after favorable launch conditions have prevailed have been computed so that mission probabilities may be more accurately computed for those time periods when persistence strongly correlates weather conditions. Moreover, the probabilities and conditional probabilities of the occurrence of both favorable and unfavorable events for each individual criterion were computed to indicate the significance of each weather element to the overall result.

King, R. L.↗

NASA NTRS1977

Biochemical responses of the Skylab crewmen: An overview

Continuous metabolic and endocrinic monitoring of Skylab crewmen established significant biochemical changes that varied in magnitude and direction but disappeared shortly after return to earth. These changes indicate adaptation by the body to the combined stresses of weightlessness. Transient changes in fluid and electrolyte metabolisms lead to the conclusion that a homeostasis condition had been achieved. Unstable states persisted in the metabolisms of bone mineral, protein, and carbohydrates.

Leach, C. S.↗

NASA NTRS1976

Solar rotation during the Maunder Minimum

Solar surface rotation has been measured from sunspot drawings made in A.D. 1642-1644, probable differences from present-day rates are found. The 17th-century sunspots rotated faster near the equator by 3 or 4%, and the differential rotation between zero and + or - 20 deg latitude was enhanced by about a factor 3. These differences are consistent features in both spots and groups of spots and in both hemispheres. It is assumed that this apparent change in surface rotation was related to the ensuing dearth of solar activity (the Maunder Minimum) which persisted until about 1715.

Eddy, J. A.↗

NASA NTRS1976

Three-dimensional aspects of interplanetary shock waves

The three-dimensional geometries of two classes of interplanetary shock waves are analyzed: (1) the more or less spherical shock wave originating from some short-lived solar event, such as a solar flare, and (2) the corotating shock pair formed by the interaction of long-lived solar wind streams. The systematic distortion of a spherical wave due to persistent latitudinal solar wind structure should amount to 25 deg for an equator-to-pole solar wind speed differential of 200 km/sec. A geometrical argument is given for determining the heliocentric distance of the onset of corotating shocks formed by contiguous long-lived solar streams. Estimates are obtained for the heliocentric distance to the inner edges of shock waves as a function of speed difference between the streams and as a function of heliographic latitude. Means by which the three-dimensional structures studied can be observed by out-of-the-ecliptic space missions are discussed.

Siscoe, G. L.↗

NASA NTRS1977

Modulation of Jovian electron intensity in interplanetary space by corotating interaction regions

Large-scale intensity variations of Jovian electrons in the energy range from 3 to 6 MeV persisting for several days were observed with instrumentation on the Pioneer 10 and Pioneer 11 spacecraft out to several AU from Jupiter along the pre- and post-planetary encounter trajectories. The corotating interaction regions (CIRs), found by Smith and Wolfe (1976) on these missions to be approximately 25-day recurring regions of enhanced magnetic fields bounded by jumps in solar-wind velocity and frequently shocks, are shown to be impenetrable 'barriers' for the Jovian electrons propagating in the interplanetary medium. Thus, the principal electron-intensity variations are due to the modulating effects of CIRs and are not due to either variations in escape rate of electrons from the magnetosphere or interplanetary electron acceleration. The implications for electron observations at the orbit of earth are discussed.

Conlon, T. F.↗

NASA NTRS1976

On flares, substorms, and the theory of impulsive flux transfer events

Solar flares and magnetospheric substorms are discussed in the context of a general theory of impulsive flux transfer events (IFTE). IFTE theory, derived from laboratory observations in the Double Inverse Pinch Device (DIPD), provides a quantitative extension of 'neutral sheet' theories to include nonsteady field line reconnection. Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction. The resulting IFTE, indifferent to the specific modes and instabilities involved, is the more energetic, the lower the initial resistivity. It is the more violent, the greater the resulting resistivity increase and the faster its growth. Violent events can develop very large voltage transients along the reconnection line. Persistent build-up promoting conditions produce relaxation oscillations in the quantity of flux and energy stored (build-up-IFTE cycles). It is difficult to avoid the conclusion: flares and substorms are examples of IFTE.

Bratenahl, A.↗