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NASA NTRS1985

Electron-density irregularities in the day-time equatorial ionosphere

Electron-density irregularities have been observed in the day-time equatorial ionosphere using probe experiments carried out in the payloads of two rockets launched near Lima, Peru during Project Condor, 1983. Simultaneous observations of the mesosphere and upper E-region were obtained using the radar at Jicamarca. A layer of mesospheric irregularities is identified as originating in neutral atmosphere turbulence. In the electrojet the rocket data show the regions of type 2 irregularities (between 90 and 105 km) and type 1 irregularities (between 103 and 108 km), differentiated by the slopes of their respective spectra. The irregularities of the upper E-region seen in the rocket data are reconciled with the radar data by postulating a strong aspect sensitivity.

Smith, L. G.↗

NASA NTRS1986

The outer atmosphere of Procyon (Alpha CMi F5IV-V) - Evidence of supergranulation or active regions

Observations made with the Einstein X-ray observatory and Exosat have shown Procyon (Alpha CMi) to have a measurable X-ray flux. The flux observed is similar to the upper limits previously reported. The interpretation of the X-ray data in the context of models made previously by Brown and Jordan (1981) based on spectra obtained with the IUE satellite. The X-ray data lead to a higher electron pressure than does the UV spectrum. These results support the conclusion by Brown and Jordan that the UV data cannot be reconciled with a hot corona in a spherically symmetric uniform model. Two types of models are explored; one in which the X-ray emission originates from an isothermal corona but the UV emission is restricted to limited regions of the disk, analogous to solar supergranulation structure; the other in which hot loop structures are embedded in a cool (T(e) of about 300,000 K) corona. Monitoring of Procyon to search for variability is urgently required to distinguish between these models. Some comparisons with the predictions of scaling laws are made. This hot isothermal coronal model agrees quite well with the predictions of Hearn's (1977) minimum flux model.

Jordan, C.↗

NASA NTRS1986

Global duricrust on Mars - Analysis of remote-sensing data

A study is conducted of the infrared thermal emission, radio thermal emission, and radar reflection data sets with the objective to obtain a simple and self-consistent model for the Mars surface. The results are compared with in situ observations at the Viking Lander sites. Attention is given to thermal inertia values, the abundance of surface rocks, radar/thermal correlations, diurnal temperature deviations, and radio emission data. It is suggested that all of the global remote-sensing data sets considered can be reconciled on the basis of variations in the degree of formation of a case-hardened crust or duricrust. On the other hand, no other model which has been proposed in conjunction with any individual data set can satisfy all of the constraints discussed.

Jakosky, B. M.↗

NASA NTRS1986

Fourier transform spectrometer observations of solar carbon monoxide. II - Simultaneous cospatial measurements of the fundamental and first-overtone bands, and Ca II K, in quiet and active regions

Fourier transform spectrometry has yielded simultaneous cospatial measurements of important diagnostics of thermal structure in the high solar photosphere and low chromosphere. It is noted that the anomalous behavior of the fundamental bands of CO in quiet areas near the limb is accentuated in an active region plage observed close to the limb. The difference between the core temperatures of the CO fundamental bands in a plage and a nearby quiet region at the limb is larger than the corresponding brightness temperature differences in the inner wings of the Ca II line measured in a quiet region and several plages closer to the disk center. Numerical simulations indicate that the disparate behavior of the CO bands with respect to Ca II K cannot be reconciled with existing single component thermal structure models; a two-component atmosphere is required.

Ayres, T. R.↗

NASA NTRS1986

Experimental investigations of trace element fractionation in iron meteorites. III - Elemental partitioning in the system Fe-Ni-S-P

Measurements of solid metal/liquid metal trace element partition coefficients, which are used to interpret the crystallization history of magmatic iron meteorite groups differ greatly between different research groups, using different experimental techniques. Specifically, partition coefficients measured utilizing 'static' experiments which approach equilibrium cannot be reconciled with the results of 'dynamic' experiments which mimic fractional crystallization. We report new tests of our 'static' experimental technique and demonstrate that our methodology yields reliable equilibrium values for Ni, P and Ge partition coefficients. Partition coefficients in the Fe-Ni-S-P system are well matched by interpolation between the Fe-Ni-S and Fe-Ni-P subsystems. In contrast, the predictions of 'dynamic' experiments do not agree with our measurements and, consequently, the ability of 'dynamic' experiments to reproduce iron meteorite Ge vs. Ni fractionation trends successfully must be regarded as fortuitous.

Malvin, D. J.↗

NASA NTRS1985

Stratospheric chemistry

Recent improvements in the data base for the currently identified reactions describing the chemistry of the major families of trace gas species, HO(x), NO(x), ClO(x), and hydrocarbons are assessed. The important coupling reactions between the families are introduced progressively. Chemical aspects such as heterogeneous reactions and reactions of sodium species, the importance of which are not yet completely established, are discussed. Recent attempts to reconcile some of the more unexpected kinetic behavior which has emerged from the extensive experimental studies of key reactions with current reaction rate theory are also examined. The uncertainties in the current kinetic and photochemical data base is given. The prospects for improvement of data for known reactions of atmospheric importance as well as for the identification of gaps in the chemical description of the atmosphere.

Cox, R. A.↗

NASA NTRS1984

Flutter optimization in fighter aircraft design

The efficient design of aircraft structure involves a series of compromises among various engineering disciplines. These compromises are necessary to ensure the best overall design. To effectively reconcile the various technical constraints requires a number of design iterations, with the accompanying long elapsed time. Automated procedures can reduce the elapsed time, improve productivity and hold the promise of optimum designs which may be missed by batch processing. Several examples are given of optimization applications including aeroelastic constraints. Particular attention is given to the success or failure of each example and the lessons learned. The specific applications are shown. The final two applications were made recently.

Triplett, W. E.↗

NASA NTRS1986

Analysis of Jovian decametric data: Study of radio emission mechanisms

Catalogues of approx. 200 decametric arcs and approx. 200 gaps between arcs were studied, in an effort to reconcile the data with predictions for the model wherein reflections of Io-induced currents each emit in a conical pattern and yield a distinct radio arc. The most recent interpretations of this data suggest that these Io-produced Alfven waves persist for at least one or two passages of Io, and that the emission cone half angles are approx. 40 to 90 deg., varying from arc to arc. Below 1.2 MHz it was discovered that Jupiter emits radiation strongly modulated in frequency with periods of approx. 200 kHz; this quasi-sinusoidal emission (MSA) can shift more than 180 deg. in phase over periods of 6 seconds, although these shifts are usually much smaller. MSA is not strongly correlated with the longitudes of Io or Jupiter, and typically occurs in patches covering approx. 500 kHz or more for periods of a few minutes. Furthermore, this modulation sometimes resembles a train of impulses in frequency with exponential decays toward high frequencies. Comparison of these results with the previous studies of V-shaped S-bursts is suggestive of an emission mechanism.

Staelin, D. H.↗

NASA NTRS1986

Alfven-wave dissipation: A support mechanism for quiescent prominences

High resolution filtergrams or spectrograms of the main body of quiescent prominences often show a very vivid dynamical picture that cannot be reconciled with static models. Even if large differences exist between individual prominences in this respect, at least parts of the prominence are usually found to be in a 'choppy', turbulent state. Evidence for systematic flows are found in local regions in the prominence and also in the transition zone in the surroundings. These two regions are probably decoupled magnetically. Alfven waves are generally believed to be responsible for the heating in the upper chromosphere and corona (Hollweg 1986). Since evidence for the presence of Alfven-waves has also been found in the solar wind field, it is highly probable that such waves are generated in the convection zone of the sun and propagated outwards in the solar atmosphere wherever a proper magnetic field is present to carry the waves. The most basic magnetic formations in the solar atmosphere are simple loops. They occur all over the solar surface and cover a large range of magnetic field strengths. Loops with the strongest magnetic fields are found in active regions. It is to be expected that the Alfven-wave flux which is channelled into the loops from below, could show considerable variation both with heliocentric latitude, with time and locally between neighbouring loops. What happens when a magnetic loop is exposed to the appropriate Alfven-wave flux required to heat the upper solar atmosphere is examined.

Jensen, Eberhart↗

NASA NTRS1987

A diffuse radar scattering model from Martian surface rocks

Remote sensing of Mars has been done with a variety of instrumentation at various wavelengths. Many of these data sets can be reconciled with a surface model of bonded fines (or duricrust) which varies widely across the surface and a surface rock distribution which varies less so. A surface rock distribution map from -60 to +60 deg latitude has been generated by Christensen. Our objective is to model the diffuse component of radar reflection based on this surface distribution of rocks. The diffuse, rather than specular, scattering is modeled because the diffuse component arises due to scattering from rocks with sizes on the order of the wavelength of the radar beam. Scattering for radio waves of 12.5 cm is then indicative of the meter scale and smaller structure of the surface. The specular term is indicative of large scale surface undulations and should not be causally related to other surface physical properties. A simplified model of diffuse scattering is described along with two rock distribution models. The results of applying the models to a planet of uniform fractional rock coverage with values ranging from 5 to 20% are discussed.

Calvin, W. M.↗

NASA NTRS1987

The surface age of Venus: Applying the terrestrial cratering rate

The population of Venusian craters having suspected impact crater morphology has been reported from 115 x 10 to the 6th power sq km of the northern hemisphere of the planet with the estimated average age of the surface to be approx. 1 b.y. (+ or - 0.5 b.y.) on the basis of lunar crater production curves corrected for Venus. Such an old average age is somewhat difficult to reconcile with the similarity in size and mass of Venus and Earth and with Earth's high heat flow and crustal resurfacing rate. Given the present uncertainties in the role of both active and inactive comet nuclei in the cratering history of Earth, it is concluded that the average age of the observed surface in the northern hemisphere of Venus could be as great as the 450 m.y. mean age of the Earth's crust. The surface of Venus might be even older, but no evidence from the crater observations support an age as great as 1 b.y.

Schaber, Gerald G.↗

NASA NTRS1987

Non-Newtonian ice rheology and the retention of craters on Ganymede

Calculations carried out for craters of varying sizes in a medium with constant temperature T = 173 K yield values for the crater relaxation time t sub e (defined as the time required for the crater depth to become 1/e of its original value) that appear to be too small to account for the observed retention of craters on Ganymede and the other icy satellites. Such a calculation is seriously in conflict with the observed crater population of the surfaces of the icy satellites. In an attempt to reconcile this conflict, possible explanations for the much slower relaxation rate of craters on the icy satellites are considered. It is possible that an admixture of silicates in the surface ice regions of the icy satellites may raise the viscosity to some extent. This possible explanation and others are briefly discussed.

Thomas, Paul J.↗

NASA NTRS1987

Characteristic structures of the highland boundary on Mars: Evidence against a single mega-impact event?

It has been suggested that an early mega-impact event might explain the fumdamental crustal dichotomy on Mars. Detailed morphological mapping of the structures which characterize the boundary between the cratered highlands and northern plains does not support this idea: the distribution of these features along and especially away from the boundary is more consistent with a larger number of smaller but overlapping impacts. A data base was assembled for the study of the highland boundary through quantitative mapping (including crater counts) based on the 1:2 M controlled photomosaics. Whole and partial craters larger than 10 km in diameter, knobby terrain, detached plateaus and intervening plains-forming units have been identified wherever they occur on Mars between +65 and -45 deg latitude. There is evidence for occurrences of possible old cratered terrain (or its remanents) at high latitudes well north of the current or likely former location of the proposed Borealis Basin rim which are difficult to reconcile with an impact structure of the proposed size and location.

Semeniuk, Ann Marie↗

NASA NTRS1986

Mass and energy balance of the cold Io torus

A new model of the cold Io torus is described. Ions and energy are injected into the system by independent processes so that the mass balance is isolated from the energy balance. The primary source of energy is local ionization and acceleration of hot pickup ions resulting from charge exchange between thermal ions and an extended cloud of Iogenic sulfur and oxygen atoms. The primary energy loss mechanism of the plasma is collisionally excited line emission at optical wavelengths. The primary ion source is radial diffusion inward from the hot torus on a time scale of 140-710 days. The primary ion loss mechanism is a novel two-step enhanced recombination mechanism involving charge exchange between thermal ions and an extended cloud of neutral SO2 molecules, followed by rapid dissociative recombination of the resultant molecular ion. The model provides a self-consistent solution which reconciles a number of diverse observations with known physical processes.

Moreno, M. A.↗

NASA NTRS1986

Comment on the letter 'On the influx of small comets into the earth's upper atmosphere. II - Interpretation'

A critical comment is made on the proposal by Frank et al. (1986) that a flux of small comets constantly impacts the earth's atmosphere. It is argued that the interpretation of the 'atmospheric holes' in terms of such an influx is difficult to reconcile with the fact that the lunar seismic network set up during the Apollo project did not detect such an influx. Frank et al. reply that this discrepancy may be traced to the insensitivity of the lunar seismic stations for the detection of the impacts of tenuous, weakly bound comets relative to those of dense, stony meteoroids.

Nakamura, Yosio↗

NASA NTRS1987

Cleopatra Patera on Venus - Venera 15/16 evidence for a volcanic origin

The nonconcentric nature, anomalous depth, and terraced morphology of the nested craters that compose Cleopatra Patera are more closely analogous to volcanic craters (calderas) than multiring impact structures. Associated deposits northeast and downslope of the Patera first recognized on Venera 15/16 radar images are interpreted as volcanic plains related to, and perhaps cogenetic with, Cleopatra. The plains lavas probably originated as effusions from a radial rift zone or ring fissures. Rim deposits surrounding Cleopatra are asymmetric along the structural fabric of the region, also indicating fissure-type eruptions. Finally, a volcanic origin not only is easily reconciled with the tectonic setting of the Patera, it is almost required by the correlation between the Patera and regional structural trend.

Schaber, Gerald G.↗

NASA NTRS1987

Does lower Omega allow a resolution of the large-scale structure problem?

The intermediate angular scale anisotropy of the cosmic microwave background, peculiar velocities, density correlations, and mass fluctuations for both neutrino and baryon-dominated universes with Omega less than one are evaluated. The large coherence length associated with a low-Omega, hot dark matter-dominated universe provides substantial density fluctuations on scales up to 100 Mpc: there is a range of acceptable models that are capable of producing large voids and superclusters of galaxies and the clustering of galaxy clusters, with Omega roughly 0.3, without violating any observational constraint. Low-Omega, cold dark matter-dominated cosmologies are also examined. All of these models may be reconciled with the inflationary requirement of a flat universe by introducing a cosmological constant 1-Omega.

Silk, Joseph↗

NASA NTRS1988

Standards For Bidirectional Reflectance And Transmittance

Sample-to-sample variations reduced. Improved reference or standard samples for measurement of bidirectional reflectance or transmittance distribution functions made by depositing single layers of spheres of same size on flat surfaces. New reference samples replicated easily and consistently, durable with moderate care. Used to reconcile different measurement facilities.

Witherow, William K.↗