Parametric representation of heat and moisture fluxes in cloud-topped mixed layers

Aircraft measurements were made from the NCAR Electra in stratus and stratocumulus clouds off the coast of California in June 1976. Several types of cloud conditions were observed, including (1) a broken layer less than 100 m thick, capped by an inversion at ~1000 m, (2) a broken stratocumulus layer ~300 m thick with an inversion at ~500 m, and (3) a solid stratocumulus layer ~250 m thick with an inversion at ~500 m. Although these observations indicate that a variety of cloud conditions may exist in mixed layers, simple one-dimensional mixed-layer models implicitly assume a solid cloud layer with no unsaturated region within the cloud. In order to generalize these simple models, a parametric representation of the heat and moisture fluxes is considered. In this scheme, the fluxes are parameterized in terms of the product of a cloud mass flux and the characteristic difference between the thermodynamic properties of an updraft-downdraft circulation. This representation allows for an explicit representation of the buoyancy flux when the downdraft has no liquid water.Data collected during these flights were used to calculate heat and moisture fluxes and to obtain the mean difference in the thermodynamic properties of the updrafts and downdrafts at a given level. The mass flux was calculated using updraft-downdraft differences and the fluxes. The mass fluxes obtained using various thermodynamic quantities are examined for consistency. The vertical distribution of the mass flux is determined. These results indicate that a mass flux formulation could prove to be useful in modeling applications where cloud conditions may vary between solid and broken.     

The geochemical behavior of refractory noble metals and lithophile trace elements in refractory inclusions in carbonaceous chondrites

Recent models of Ca, Al-rich inclusion (CAI) petrogenesis suggest that refractory inclusions may be residues of interstellar dust aggregates that were incompletely evaporated and partially melted in the solar nebula. These models, and the recent availability of new thermodynamic data, have led us to re-examine the traditional interpretation that lithophile refractory trace elements (LRTE) condensed as oxides in solid solution in refractory major condensates, while refractory noble metals (RNM) condensed as micron-sized nuggets of Pt-metal alloys. Calculations of LRTE-RNM alloy stability fields under nebular oxygen fugacities and partitioning experiments lead us to conclude that: (1) Ti, Zr, Nb, Hf, U, and Ta form stable alloys with RNM under nebular conditions; (2) the observation that metallic Zr, Nb, and Ta occur in some Pt-metal nuggets and grains is explained by the stability of these LRTE-RNM alloys under normal nebular oxygen fugacities; (3) metallic Ti, Hf, and U may also occur in some nuggets; (4) the lanthanides, the other actinides (Th, Pu), and Y do not form stable alloys, and thus probably do not occur alloyed with RNM; and (5) the partitioning of U (but not Th, Pu, or the REE) into RNM is a novel actinide and REE/actinide fractionation mechanism that is based on metal/silicate fractionation (rather than on the relative volatility of their oxides).We propose that micron-sized Pt-metal nuggets formed from smaller grains of RNM alloys and compounds during the evaporation and melting of primitive dust aggregates. This process would have been enhanced by: (1) the possibility that the RNM were present as compounds (especially with As and S) as well as metallic alloys in interstellar dust and in some primitive meteoritical material, since they often exhibit non-siderophile behavior; and (2) the fluxing of volatiles through CAI's during distillation. Microscopic nuggets are common in melilite chondrules, indicating that residence in a slowly-cooled silicate melt may have favored their formation. Cation diffusivity and variations in localf_O2 can explain why metallic LRTE-bearing nuggets are not common in CAI's (despite the relative stability of LRTE-RNM alloys). We propose that the lithophile component of Fremdlinge is enriched in super-refractory elements, and that Group II CAI's formed from Fremdlinge-poor dust. We interpret the Group II REE fractionation as a pre-solar event, and predict that Nd/Sm dating will yield an age greater than the canonical age of the solar system. If metal/silicate fractionation in a cold solar nebula can explain Group II REE patterns, the possibility that Group II CAI's are also distillation residues cannot be excluded.     

Distribution of partial melt in a felsic system: the importance of surface energy

The texture, distribution, and infiltration tendency of a quartz-albite melt in equilibrium with a synthetic, texturally-equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1,250° C and 8 kbar hydrostatic pressure. Wetting angle measurements from melt distribution experiments show a dihedral angle () of 60 degrees, implying a quartz/quartz interfacial energy approximately 1.7 times the quartz/melt value. Because of this specific relationship between interfacial energies, the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections, possibly forming some interconnected channels. Stability of melt in pockets and along grain edge intersections was observed in a fourteen-day, dispersed-melt experiment, yet melt pools failed to disperse into the quartzite during infiltration experiments. Comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement, and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically.While these experiments are not strictly applicable to real crustal systems, they do indicate that, at least in some felsic systems, the melt has no preference for uniform grainedge wetting relative to collection at grain corners or in large pools. This ambivalent behavior is attributable to the 60-degree wetting angle, which has been shown to separate systems in which melt tends to disperse in interconnected channels (<60°) from those in which melt tends to become isolated at grain corners (> 60°).     

Erratum: the 2.27 day period of WR-134 (HD 191765)

The original temporal analysis of a 12 night spectral timeseries of WR-134 has been found to be flawed and a re-analysis shows that the line profile variations are indeed periodic. When combined with a 4 night timeseries taken 45 days earlier, a period near 2.27 d is found in periodograms of the Heii 5412 line centroid,rms line width, and line skew variations. When the emission line residuals are ordered as a function of phase, a sinuous feature appears to snake about the line center with an amplitude of ± 500 km s^–1. This is 20 larger than the line centroid amplitude; the calculation of which is heavily weighted by static portions of the line profile. In addition to the snake, emission residuals appear that move away from line center on unbound trajectories and are thought to result from the interaction of a periodic driver with the unstable flow of the radiation driven wind. The nature of the periodic driver is a topic for discussion.     

Sedimentologic and stratigraphic constraints on emplacement of the Star Kimberlite, east–central Saskatchewan

Diamond-bearing kimberlites in the Fort à la Corne region, east–central Saskatchewan, consist primarily of extra-crater pyroclastic deposits which are interstratified with Lower Cretaceous (Albian and Cenomanian) marine, marginal marine and continental sediments. Approximately 70 individual kimberlite occurrences have been documented. The Star Kimberlite, occurring at the southeastern end of the main Fort à la Corne trend, has been identified as being of economic interest, and is characterized by an excellent drill core database. Integration of multi-disciplinary data-sets has helped to refine and resolve models for emplacement of the Star Kimberlite. Detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex. Micropaleontologic and biostratigraphic analysis of selected sedimentary rocks, and U–Pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement. Radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at Star. The oldest kimberlite in the Star body erupted during deposition of the predominantly continental strata of the lower Mannville Group (Cantuar Formation). Kimberlites within the Cantuar Formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate. Successive eruptive events occurred contemporaneous with deposition of the marginal marine upper Mannville Group (Pense Formation). Kimberlites within the Pense Formation consist primarily of terrestrial airfall deposits. Fine- to medium-grained cross-stratified kimberlitic (olivine-dominated) sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression. The location of the source feeder vents of the Cantuar and Pense kimberlite deposits has not been identified. The youngest and volumetrically most significant eruptive events associated with the Star Kimberlite occur within the predominantly marine Lower Colorado Group (Joli Fou and Viking Formations). Kimberlite beds, which occur at several horizons within these units, consist of subaerial and marine fall deposits, the latter commonly exhibiting evidence of wave-reworking. Black shale-encased resedimented kimberlite beds, likely deposited as subaqueous debris flows and turbidites, are particularly common in the Lower Colorado Group. During its multi-eruptive history, the Star Kimberlite body is interpreted to have evolved from a feeder vent and overlying positive-relief tephra ring, into a tephra cone. Initial early Joli Fou volcanism resulted in formation of a feeder vent (200 m diameter) and tephra ring. Subsequent eruptions, dominated by subaerial deposits, partly infilled the crater and constructed a tephra cone. A late Joli Fou eruption formed a small (70 m diameter) feeder pipe slightly offset to the NW of the early Joli Fou feeder vent. Deposits from this event further infilled the crater, and were deposited on top of early Joli Fou kimberlite (proximal to the vent) and sediments of the Joli Fou Formation (distal to the vent). The shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the Lower Colorado Group, resulting in wave-reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits (tempestites, turbidites, debris flows) in more distal settings.     

The Queens' flare: Its structure and development; precursors,pre-flare brightenings,and aftermaths

We continue previous research on the limb flare of 30 April, 1980, 20:20 UT, observed in X-rays by several instruments aboard the Solar Maximum Mission (SMM). It is shown quantitatively that the flare originated in an emerging magnetically confined kernel (diameter ～ 20″) which existed for about ten to fifteen minutes, and from which energetic electrons streamed, in at least two injections, into a previously existing complicated magnetic loop system thus forming a less bright but extended and long-lived tongue. The tongue had a length of ～ 35 000 km and lasted ～ 90 min in X-rays (～ 10 keV); at lower energies (～ 0.7 keV) it was larger (～ 80 000 km) and lasted longer. The total number of energetic electrons (≈ 10³⁷) initially present in the kernel is of the same order as the number present in the tongue after the kernel's decline. This gives evidence that the energetic electrons in the tongue originated mainly in the kernel. The electron number densities in the kernel and tongue at maximum brightness were ～ 4.5 × 10¹¹ and ～ 1 × 10¹¹ cm^#X2212;3, respectively. During the first eight minutes of its existence the tongue was hotter than the kernel, but it cooled off gradually. Its decline in intensity and temperature was exponential; energy was lost by radiation and by conduction through the footpoints of the loop system. These footpoints have a cross-section of only ～ 3 × 10⁶ km². This small value, as well as photographs in a Civ UV emission line, suggests a highly filamentary structure of the system; this is further supported by the finding that the tongue had a ‘filling factor’ of ～ 10^#X2212;2. Several faint X-ray brightenings (? 0.005 of the flare's maximum intensity) were observed at various locations along the solar limb for several hours before and after the flare. At ～ 30 min before the flare's onset a faint (? 0.02) flare precursor occurred, coinciding in place and shape with the flare. First the kernel precursor was brightest but the tongue precursor increased continuously in brightness and was the brightest part of the precursor some 10–15 min after the first visibility of the kernel precursor, until the start of the main flare. This suggests (weak) continuous electron acceleration in the tongue during a period of at least 30 min. The main flare was caused by strong emergence of magnetic field followed by two consecutive field line reconnections and accelerations in a small loop system, causing footpoint heating. Subsequently plasma streamed (convectively) into a pre-existing system of larger loops, forming the tongue.     

Mars: Subsurface properties from observed longitudinal variation of the 3.5-mm brightness temperature

Measurements at 3.5 mm of the disk-average brightness temperature of Mars during the 1978 opposition can be represented by

$\text{T}{}_{\mathrm{B}}\text{(Mars, 3 5 mm, Jan/Feb 1978)}\text{=}\textcolor{red}{}$

(The errors cited are from the internal scatter; the estimated absolute calibration uncertainty is 3%.) This longitudinal variation must be taken into account if Mars is to be used as a calibration source at millimeter wavelengths. The total range of the 3.5-mm variation is three to four times larger than both the 2.8-cm and 20-μm variations. This unexpected result can possibly be explained by subsurface scattering from rocks ?1.5-cm radius.