The Leonard Award Address Presented 1996 July 25, Berlin,Germany: The elemental composition of stony cosmic spherules

Abstract— Five hundred stony cosmic spherules collected from deep-sea sediments, polar ice, and the stratosphere have been analyzed for major and some minor element composition. Typical spherules are products of atmospheric melting of millimeter sized and smaller meteoroids. The samples are small and modified by atmospheric entry, but they are an important source of information on the composition of asteroids. The spherules in this study were all analyzed in an identical manner, and they provide a sampling of the solar system's asteroids that is both different and less biased than provided by studies of conventional meteorites. Volatile elements such as Na and S are depleted due to atmospheric heating, while siderophiles are depleted by less understood causes. The refractory nonsiderophile elements appear not to have been significantly disturbed during atmospheric melting and provide important clues on the elemental composition of millimeter sized meteoroids colliding with the Earth. Typical spherules have CM-like composition that is distinctively different than ordinary chondrites and most other meteorite types. We assume that C-type asteroids are the primary origin of spherules with this composition. Type S asteroids should also be an important source of the spherules, and the analysis data provide constraints on their composition. A minor fraction of the spherules are melt products of precursor particles that did not have chondritic elemental compositions. The most common of these are particles that are dominated by olivine. The observed compositions of spherules are inconsistent with the possibility that an appreciable fraction of the spherules are simply chondrules remelted during atmospheric entry.     

Microstructures in type III events in the solar wind

A model is presented for the generation and evolution of bump-in-tail driven Langmuir waves in the solar wind during type III emission, which removes a number of apparent inconsistencies between theory and observations. It is argued that there must be localized enhancements of f _b /v by a factor of 10² over the measured average values. Growth rates and energy densities of Langmuir waves are, therefore, considerably enhanced, permitting growth to overcome linear scattering losses, and also allowing nonlinear decay into ion-acoustic waves, in line with observations. Estimates are made of the probability distribution p(E), of wave field strengths E, based on linear and nonlinear wave-packet evolution, yielding p(E) E ^–a, 3. This helps explain why very high values of E are rarely found in the measured spiky wave turbulence.     

Ultraviolet solar irradiance measurement from 200 to 358 nm during spacelab 1 mission

The paper presents the results obtained from the UV-spectrometer of the Solar Spectrum Experiment during the Spacelab 1 mission in December 1983. The irradiance data concern 492 passbands, which are located between 200 and 358 nm at almost equidistant wavelengths separated by about 0.3 nm. The passbands have a well-defined, bell-shaped profile with a full width at half maximum of about 1.3 nm. The data, which have an error budget between 4 and 5%, agree closely with the spectral distributions observed by Heath (1980) and Mentall et al. (1981) and confirm that the solar irradiance and the fluxes of Sun-like stars show about the same spectral distribution down to at least 240 nm.     

The nature and significance of the feedback of changes in terrestrial vegetation on global atmospheric and climatic change

The potential feedback on global atmospheric and climate change of climate-driven changes in terrestrial vegetation is examined by systematically relating the surface exchanges of energy, mass and momentum to two dimensions of vegetation, structure and taxonomy, such that the significance of climate driven changes in these characteristics can be assessed. A detailed quantitative understanding of this feedback is an important prerequisite to realistic and dynamic representations of the Earth's surface within general circulation and biological models (GCMs and GBMs). Without realistic representations of terrestrial vegetation within these models, any forecasts of future climates by these models must be suspect.Several general conclusions are drawn. The first is that the indirect feedbacks, those associated with the clouds and aerosols of the planetary boundary layer, appear to be very powerful but as yet their behaviour and connections with the underlying surface are both poorly understood and captured within GCMs.The physical structure of vegetation, the disposition of biomass in 3-D, is the characteristic that most strongly influences the exchange of momentum (via aerodynamic roughness) and solar radiation (via albedo). Vegetation structure and species composition determine the most important of the mass exchanges, evapotranspiration. Of all of the surface exchanges, the parameterization of evapotranspiration (E ) and the simulation of the water balance over time is the most critical.Lastly, the problems of scaling and spatial heterogeneity, the sub-grid variability of the modellers, looms as a difficult, but not insoluble, problem. It remains a critical problem however, and the detailed parameterization of the various big leaf models stands in absurd contrast to the simplistic generalization of the spatial heterogeneity of terrestrial landscapes.Plant ecologists can contribute to the task of improving the representation of vegetated landscapes within GCMs. There is need to simply and unify the way in which vegetation can be grouped at landscape scales. A classification that is based on function rather than phylogeny is required. The definition of Vegetation Functional Types (VFTs) would expedite research on both the impact of, and feedback on, climate change.     

Implications of liouville's theorem on the apparent brightness temperatures of solar radio bursts

Liouville's theorem for radiation, of which the generalized étendue is a consequence, implies ² d² d² A = constant along the ray path, where is the refractive index and d² and d² A are the ranges, respectively, of solid angle and of area that define a ray (actually a bundle of rays). Implications of this concept on the propagation of radio waves from the actual to the apparent source in the solar corona (i.e., the scatter image of the true source) are discussed. The implications for sources of fundamental plasma radiation include: (1)The observed solid angle (defining the directivity) and apparent area A of the source are compatible with Liouville's theorem only if the apparent source (the scatter image of the true source) corresponds to the envelope of subsources with a small filling factor f. (2) The brightness temperature T _Bof the actual source is greater than that of the apparent source by f ^-1. (3) For sources of fundamental plasma radiation the factor f is very small ( 10^-2). (4) A long-standing discrepancy between the observed low value of T _B at meter/decameter wavelengths for the quiet Sun and the known coronal temperature may be resolved by noting that the implied coronal temperature is given by T _B f and that the factor f must be significantly less than unity.A brief discussion is included of the relation between Liouville's theorem, the generalized étendue, Milne's laws, occupation numbers, extension in phase, and suppression of emission by a medium with refractive index unequal to unity.     

Effects of mass transfer on an oscillating free-convection flow in the Stokes's problem past an infinite porous vertical limiting surface with heat sources and variable suction

An analysis of the effects of the mass transfer on the unsteady free-convection flow of a viscous incompressible fluid, past an impulsively started infinite porous vertical limiting surface with heat sources is presented, when the free-stream velocity and the suction velocity, are oscillating in the time about constant mean values. Approximate solutions for the coupled nonlinear equations are derived for the mean velocity, the mean temperature, the mean skin-friction, and the mean rate of heat transfer. All the above quantities are shown graphically followed, by a discussion.     

Nature of the symbiotic binary V 1329 Cyg

The published photometric and spectroscopic data of the symbiotic binary V 1329 Cyg are interpreted. It is shown, that V 1329 Cyg is an eclipsing binary with an elliptical orbit orbit (e=0.28). The cooler component fills up the Roche-lobe at periastron. A model of moving gaseous structures in the system is proposed and their influence on the radial velocity curve is shown. The following characteristics of the system are derived: the cooler component is an M6 giant with mass 7.9M , radius 339R and luminosityM _bol=–5.42, the hot component is a white dwarf surrounded by an accretion disk. The mean distance between the components is 842R and in periastron it decreases to 605R .     

Bianchi type-II perfect fluid solutions

It is shown that the recent new Bianchi type-II solutions of Hajj-Boutros (1986a, b) do not exist. We present a consistent method for perfect fluid solutions in this paper.     

A note on the total mass of comets in the solar system

The assumption that the very low albedo determined for Halley's comet is typical of all short period comets, taken together with the assumption that the average sizes of long and short period comets are approximately equal, leads to an increase in the total mass of comets in the solar system by almost two orders of magnitude. If gravitational ejection from the Uranus - Neptune zone during the later phases of planet formation is indeed responsible for the classical Oort cloud between 10⁴–10¹⁵ AU, then the mass of comets in this transplanetary region during cosmogonie times has to exceed the combined masses of Uranus and Neptune by over an order of magnitude. Furthermore, if the recent arguments for as many as 10¹⁴ comets in an inner Oort cloud between ~40– 10⁴AU are valid, then the total mass of comets in the solar system approaches 2% of a solar mass.     

An UV survey of the galactic plane

The present paper is the introduction to a systematic analysis of 123 6-degree fields near the galactic plane, recorded in the medium ultraviolet (2000 Å) by the ballon-borne experiment SCAP 2000 of the Laboratoire d'Astronomie Spatiale, Marseille, and Geneva Observatory. The available data are presented and the general properties of the images are briefly discussed.It is shown that the high selectivity of the UV passband regarding spectral type, together with the strong interstellar extinction at that wavelength, provide the necessary conditions for an efficient application of Wolf's method to study the distribution of interstellar matter in the solar neighbourhood. The results of a fast analysis of the available data are presented here.