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NASA NTRS1983

AVE/VAS experiment: Synoptic summary and preliminary results

The AVE/VAS ground truth field experiment was conducted during the Spring of 1982 severe storms and weather research program. The experiment consisted of acquiring correlative ground truth measurements of rawinsonde data, corresponding to the time and space resolutions of VAS sounding data. The objectives of the AVE/VAS experiment are: (1) to acquire four dimensional data sets of the actual atmospheric structure down to the mesoscale; (2) to provide measurements for quantitative comparisons between ground based and VAS-derived atmospheric parameters; (3) to evaluate the impact of VAS data on diagnostic analysis of structural features and dynamical processes important to the development of mesoscale phenomena; (4) to evaluate the impact of VAS data on numerical model simulations, nowcasting, and other mesoscale forecasting systems.

Jedlovec, G. J.↗

NASA NTRS1983

Fundamental combustion experiments in microgravity

Technical bases for microgravity combustion experimentation are identified for important areas of study. The analyses which underlie the need for microgravity experiments of single and two-phase autoignitions, explosions, thermokinetic oscillations, and kinetic oscillations are emphasized. It is shown that turbulent combustion experiments at microgravity are needed and that heterogeneous kinetics are a centrally important process in a number of classic experiments.

Berlad, A. L.↗

NASA NTRS1982

Departure from corotation of the Io plasma torus - Local plasma production

The departure of the Jovian magnetosphere from rigid corotation is adequately explained by outward plasma transport at distances where L is greater than approximately 10. The departure of 5% observed in the Io plasma torus, however, is too large to be accounted for simply by plasma transport. Local plasma production is proposed as the main factor determining the corotation lag in the torus. The outward pick-up current provided by ionization of neutral atoms is calculated and related to the current produced in the ionosphere by the corotation lag. This leads to an expression giving the corotation lag of the torus as a function of radial distance. Charge transfer is found to be an important process, allowing the majority of the torus mass to be ejected from the magnetosphere in a neutral state. Thus, the mass loading rate is found to be several times that inferred from examination of the corotation lag associated with outward plasma transport.

Pontius, D. H., Jr.↗

NASA NTRS1982

Recent developments in multi-wire fixed abrasive slicing technique (FAST)

Slicing is an important processing step for all technologies based on the use of ingots. A comparison of the economics of three slicing techniques shows that the fixed abrasive slicing technique (FAST) is superior to the internal diameter (ID) and the multiblade slurry (MBS) techniques. Factors affecting contact length are discussed, taking into account kerf width, rocking angle, ingot size, and surface speed. Aspects of blade development are also considered. A high concentration of diamonds on wire has been obtained in wire packs usd for FAST slicing. The material removal rate was found to be directly proportional to the pressure at the diamond tips.

Schmid, F.↗

NASA NTRS1983

Equilibria in Strongly Magnetized Pair Plasmas

Positron-electron pair densities for a thermal plasma in the steady-state equilibrium where pair production balances pair annihilation are found as a function of temperature kT / mc(2) approx. 1, source size R and magnetic field strength B. When the plasma is strongly magnetized, B 10(12) G, the important processes are synchrotron radiation, one-photon (magnetic) pair production and two-photon pair annihilation. An analytic solution for the equilibrium pair density, found under certain simplifying assumptions, shows that optically thin equilibria exist only for sufficiently small source sizes.

Harding, A. K.↗

NASA NTRS1984

Properties of simulated comet mantle

The properties of freeze-dried dilute dispersions of dust in water ice are of considerable interest in studies of comet nucleus mantles. The formation of a rind residue produced by the sublimation of water ice containing various amounts of fine clay particles may be an important process. A simulation of the development of the dry dust rind on the surface of comets is presented. This rind is the result of preferential ice sublimation. The development and disruption of this rind and its subsequent levitation by water vapor flow is studied. The most interesting rind simulant is produced by dispersing 0.1 micron particles of montmorillonite in water in concentrations of 10%, 1%, and 0.1%. These dispersions are then sprayed into liquid nitrogen in the form of 100 micron droplets. The frozen droplets are then freeze-dried in a vacuum which prevents the ice temperature from rising above -30 C. Sublimation of the nitrogen and the water produced dry rinds. The most striking result was the development of large cohesive matrices of individual clay particles, and in some cases a continuous cohesive crust. Scanning electron microscope (SEM) observations reveal that the material formed by freeze-drying the 0.1% dispersion does not retain the original spherical shape of the sprayed 100 micron droplets; instead it consists of a continuous filamentary network, as shown in the SEM stereo micrographs.

Fanale, F. P.↗

NASA NTRS1984

Some contributions to knowledge of the magnetospheric plasma by ISEE investigators

The ISEE project has made substantial contributions to the knowledge of the magnetosphere during the period of the IMS, especially in the discipline of Space Plasma Physics. Results obtained during approximately the first two years of the operation of ISEE-1 and -2, and touches on relevant results of ISEE-3 are reviewed. The ability to control the separation between ISEE-1 and -2, which are in nearly identical orbits, has permitted study of the motion and structure of the bow shock and magnetopause, the boundary layers, and the plasma sheet. Much evidence was obtained favoring the existence of reconnection and its relevance to the transfer of magnetic flux from the frontside to the rear of the magnetosphere, although not everyone agrees that it is the only important process. The presence of both reflected and accelerated particles was shown to lead to the development of a foreshock region between the bow shock and the interplanetary magnetic field line tangential to it.

Ogilvie, K. W.↗

NASA NTRS1982

Model calculations of lightning electric fields

Calculated time-domain waveforms and frequency spectra are presented for three of the most important processes in a lightning discharge to ground: the return stroke, the stepped leader, and the preliminary breakdown. For each of these processes, the model calculations are given for 200 m and 50 km. The calculations are compared with available time and frequency domain measurements.

Master, M. J.↗

NASA NTRS1984

Mechanisms of nitrogen retention in forest ecosystems - A field experiment

Intensive forest management led to elevated losses of nitrogen from a recently harvested loblolly pine plantation in North Carolina. Measurements of nitrogen-15 retention in the field demonstrated that microbial uptake of nitrogen during the decomposition of residual organic material was the most important process retaining nitrogen. Management practices that remove this material cause increased losses of nitrogen to aquatic ecosystems and the atmosphere.

Vitousek, P. M.↗

NASA NTRS1984

Numerical Modeling of the Atmosphere

Numerical models and numerical analyses of observations were used to improve the understanding of the physical processes important in global weather and climate. Results from a study of the effect of baroclinic waves on mid-latitude vertical temperature structure show that the waves' vertical eddy heat flux tend to eliminate the potential vorticity gradient near the steering level by causing the static stability to decrease rapidly with height in the lower troposphere above the boundary layer. An empirical study of the relationship between eddy heat fluxes and the meridional temperature gradient has been completed. The results indicate that the feedback in the flux-gradient system is comparable to dissipation on all time scales between the synoptic and the seasonal. The definition of the Eliassen-Palm flux and the Eliassen-Palm and non-acceleration theorems has been generalized to include eddy forcing of condensation. Calculations based on the generalized diagnostics showed that the annual mean eddy forcing of the zonal mean zonal wind is two and one half times stronger when the condensation effects are included.

Stone, P. H.↗

NASA NTRS1985

Considerations of large scale impact and the early Earth

Bodies which have preserved portions of their earliest crust indicate that large scale impact cratering was an important process in early surface and upper crustal evolution. Large impact basins form the basic topographic, tectonic, and stratigraphic framework of the Moon and impact was responsible for the characteristics of the second order gravity field and upper crustal seismic properties. The Earth's crustal evolution during the first 800 my of its history is conjectural. The lack of a very early crust may indicate that thermal and mechanical instabilities resulting from intense mantle convection and/or bombardment inhibited crustal preservation. Whatever the case, the potential effects of large scale impact have to be considered in models of early Earth evolution. Preliminary models of the evolution of a large terrestrial impact basin was derived and discussed in detail.

Grieve, R. A. F.↗

NASA NTRS1985

On magnetic pair production above fast pulsar polar caps

Magnetic pair production is one of high-energy electromagnetic conversion processes important to the development of pair-photon cascades in pulsars. On the basis of current polar cap models, the properties of magnetic pair production in fast pulsars are discussed. Suppose there is a roughly dipole magnetic field at the stellar surface, the author estimate the effects on non-zero curvature of magnetic field lines upon curvature radiation from primary particles and pair production rate near the surface of pulsars.

An, S.↗

NASA NTRS1984

Mixing and the dynamics of the deep chlorophyll maximum in Lake Tahoe

Chlorophyll-temperature profiles were measured across Lake Tahoe about every 10 days from April through July 1980. Analysis of the 123 profiles and associated productivity and nutrient data identified three important processes in the formation and dynamics of the deep chlorophyll maximum (DCM): turbulent diffusion, nutrient supply rate, and light availability. Seasonal variation in these three processes resulted in three regimes: a diffusion-dominated regime with a weak DCM, a variable-mixing regime with a pronounced, nutrient supply-dominated DCM, and a stable regime with a deep, moderate light availability-dominated DCM. The transition between the first two regimes occurred in about 10 days, the transition between the last two more gradually over about 3 weeks. The degree of spatial variability of the DCM was highest in the second regime and lowest in the third. These data indicate that the DCM in Lake Tahoe is constant in neither time nor space.

Abbott, M. R.↗

NASA NTRS1985

A systematic study of magnetic braking in low-mass binaries

A short summary is given of Rappaport et al. (1983) which described results of extending a simplified stellar evolution code covering the evolution of low-mass compact binaries. Magnetic braking is probably an important process in the evolution of such binaries (such as cataclysmic variables and low-mass X-ray sources). The initial simplified code describes the mass-losing star as an n = 3/2 polytrope and was developed to study the evolution of binaries with a secondary of low mass (between 0.01 and 0.4 solar mass) when the angular momentum losses are due to gravitational radiation. In the extended code, a composite polytrope model is used for the secondary, wherein the structure of the radiative core is described by an n = 3 polytrope and the convective envelope by an n = 3/2 polytrope.

Verbunt, F.↗

NASA NTRS1985

Fusion Target Technology

In order to produce the high quality spherical shells that are required, three parameters must be controlled accurately: the shell dimensions, shell sphericity and concentricity, and the surface topology of the shell. Attempts to conduct experiments on the dynamics of liquid bubbles (molten shells) in laboratories are limited by a strong coupling among the three parameters, time, gravity, and temperature. These limitations are circumvented and detailed study of each of the important processes is carried out through the use of low gravity environments collectively available in drop towers, in KC-135 flights, in a neutrally buoyant immiscible system, and in an acoustic levitation system.

Wang, T. G.↗

NASA NTRS1985

Ion partitioning in the hot Io torus - The influence of S2 outgassing

An alternative time-independent model of the ion partitioning in the hot Io torus is proposed which introduces the ratio of sulfur to oxygen in the neutral source as a free parameter. Measurements of the ion abundances in the torus plasma are presented and discussed, noting some ambiguities and identifying the features that are well established. Physical processes important to the understanding of the ion partitioning calculation are reviewed. The results of the model are discussed in the context of observational constraints, and spectroscopic constraints are discussed. It is concluded that a bimodal source model, together with a small percentage of hot electrons and a relatively short diffusion time scale, can account for the principal observational features without invoking significant time variability. In particular, the O III deficiency observed in 1981 can be obtained in a model that produces other aspects of the torus ion partitioning measured during the Voyager 1 encounter.

Moreno, M. A.↗

NASA NTRS1987

Mantle convection and the state of the Earth's interior

During 1983 to 1986 emphasis in the study of mantle convection shifted away from fluid mechanical analysis of simple systems with uniform material properties and simple geometries, toward analysis of the effects of more complicated, presumably more realistic models. The important processes related to mantle convection are considered. The developments in seismology are discussed.

Hager, Bradford H.↗

NASA NTRS1987

The role of regolith adsorption in the transition from early to late Mars climate

Researchers reexamined radiative transfer models of early Mars that were advanced to show the existance of a greenhouse effect. These models were reexamined with regard to the effect that regolith adsorption may have had. It is argued that while the precipitation of carbonates has probably been an important process during Mars history, the rates at which this process could have taken place under early Mars conditions would have dropped sharply once liquid water was fairly scarce. Furthermore, conditions under which liquid water was available may have involved efficient recycling of carbonate so that steady state conditions rather than irreversible CO2 removal prevailed. In contrast, the growth of regolith surface area demands corresponding and predictable CO2 removal from the atmosphere-cap system and is fully capable of terminating any enhanced temperature regime on early Mars in the absence of any other effects.

Fanale, F. P.↗