Numerical study of droplet size dependent chemistry in oceanic,wintertime stratus cloud at southern mid-latitudes

Cloud droplet chemistry is modelled for the first 150 m of rise in a wintertime, mid-latitude, marine stratus cloud using observations made at and near the Cape Grim Baseline Station as a source of input parameters. The emphasis in this work was to study the variation in droplet chemistry as a function of both droplet size and nucleus composition, with a particular focus on the way in which oxidation of dissolved sulfur dioxide varied.At 150 m above the condensation level, solute concentration as a function of droplet size was found to increase by as much as 2 to 3 orders of magnitude for only a factor of 2 increase in droplet radius, primarily as a consequence of the 1/r dependence in the droplet growth equation. This type of size dependence exists at all levels in the model cloud, and has a significant influence on oxidation rate of sulfur dioxide in droplets growing on sulfate nuclei, oxidation by ozone being favoured in the smallest droplets, but oxidation by hydrogen peroxide being favoured in the larger droplets. Oxidation by ozone is favoured at all sizes in droplets formed on sea-salt nuclei as a result of the initially high alkalinity of these droplets, and in the cloud overall is calculated to be the more important oxidation pathway. Although based on a simplified chemical scheme, these results suggest that both size-dependent and nucleus-dependent chemistry of cloud droplets may need to be considered explicitly in cloud modelling work.Volume-weighted mean pH values in the range 5 to 6 were predicted from sensitivity studies in which input variables were varied over reasonable ranges, in agreement with two sets of bulk cloud-water pH data obtained by aircraft near Cape Grim.     

Structure of the marine boundary layer over north western Indian Ocean during 1983 summer monsoon

The spatial variability of the structure of the lower troposphere over the northwestern Indian Ocean for the period 12th July to 2nd September, 1983 has been studied using upper air data collected during the first scientific cruise of ORV Sagar Kanya.An analysis of thermodynamic structure and kinematics of the marine boundary layer for different zonal and meridional sections revealed the following features: (a) Temperature and humidity inversions were generally absent over the study area except over a few locations in the western region; (b) Large-scale subsidence was found over the central equatorial Indian Ocean; (c) The convective activity over the western Indian Ocean was found to be moderately suppressed as compared to the eastern region; (d) The zonal and meridional components of winds along the equator and 10° N zonal section exhibited a mirror-image-like distribution.     

Petrology,isotope characteristics,and K-Ar ages of the Maranhão,northern Brazil,Mesozoic basalt province

Northern Brazil contains remnants of Mesozoic flood basalts and hypabyssal rocks that were apparently emplaced during tectonism related to opening of the Atlantic Ocean. Analyses and new K-Ar ages reveal that this 700x250 km Maranhão province (5°–8°S) has low-Ti basalts (1.1 wt% TiO₂) in the western part that range about 160 to 190 Ma, and high-Ti basalts (3.4–4.4 wt% TiO₂) in the eastern part about 115–122 Ma. Low-Ti basalt compositions are less evolved and have a smaller range, Mg# 62-56, than the high-Ti basalts, Mg# 44–33. General characteristics of the least evolved members of low- and high-Ti groups include, respectively, Zr 100 and 250 ppm, Sr 225 and 475 ppm, Ba 200 and 500 ppm, Nb 10 and 26 ppm, Y 29 and 36 ppm, La/Yb_(n) 4.2 and 8.8, where La_(n) is 30 and 90. Overall compositions resemble the low- and high-Ti basaltic rocks of the Mesozoic Serra Geral (Paraná) province in southern Brazil. The Maranhão low-Ti basalts have more radiogenic Sr and Pb and higher ¹⁸O than the high-Ti basalts. Respectively, low- vs high-Ti: _Sr26–54 vs 15–18; ²⁰⁶Pb/²⁰⁴Pb=18.25–.78 vs 18.22–.24; and ¹⁸O 8.9–12.6 vs 6.5–8.6. Nd isotopes overlap: _Nd–1.6 to –3.8 vs –2.1 to –3. Ages, compositions, and isotopes indicate that the low- and high-Ti groups had independent parentages from enriched subcontinental mantle. However, both groups can be modeled from one source composition if low-Ti basalt isotopes reflect crustal contamination, and if the parentages for each group were picritic liquids that represent either higher (for low-Ti) or lower (for high-Ti) percentages of melting of that single source. When comparing Pb isotopes of Maranhão and Serra Geral high-Ti basalts (uncontaminated) to evaluate the DUPAL anomaly, Maranhão has Pb 7/4=4.6–11, and Pb 8/4=72–87; Serra Geral has Pb 7/4=10–13, and Pb 8/4=95–125. The small difference is not enough to conform to DUPAL contours, and is inconsistent with large-scale isotopic heterogeneity of mantle beneath Brazil prior to rifting of South America from Africa. Maranhão low-Ti magmas probably relate to the opening of central North Atlantic, and high-Ti magmas to the opening of equatorial Atlantic. The proposed greater percentage of source melting for low-Ti basalts may reflect a Triassic-Jurassic hotspot, while lesser melting for high-Ti magmas may relate to Cretaceous decompressional (rifting) melting.     

The distribution of infrared sources in the galactic plane

A study of the galactic structure has been made by deriving the brightness distribution of the galactic plane at 2.2 m and 4.2 m near infrared region using infrared objects detected by ground-based sky surveys. The infrared brightness distribution shows distinct peaks at every 8–12° galactic longitude and indicates a periodic structure. The one-to-one positional correlation observed between the periodic structure in 2.2 m infrared brightness and the 2.6 mm CO emission line suggests that the near-infrared sources are strongly associated with dense clouds of molecular hydrogen distributed in the galactic plane.     

Hill stability of satellite orbits

Szebehely's criterion for Hill stability of satellites is derived from Hill's problem and a more exact result is obtained. Direct, Hill stable, circular satellites can exist almost twice as far from the planet as retrograde satellites. For direct satellites the new result agrees with Kuiper's empirical estimate that such satellites are stable up to a distance of half the radius of action of the planet. Comparison with the results of numerical experiments shows that Hill 'stability is valid for direct satellites but meaningless for retrograde satellites. Further accuracy for the maximum distance of Hill stable orbits is obtained from the restricted problem formulation. This provides estimates for planetary distances in double star systems.     

Formation of the Bencubbin polymict meteoritic breccia

The Bencubbin meteorite is a polymict breccia consisting of a host fraction of ~60% metal and ~40% ferromagnesian silicates and a selection of carbonaceous, ordinary and ‘enstatite’ chondritic clasts. Concentrations of 27 elements were determined by neutron activation in replicate samples of the host silicates and the ordinary and carbonaceous chondritic clasts; 12 elements were determined in the host metal. Compositional data for the ordinary chondrite clast indicate a classification of LL4 ± 1. Refractory element data for the carbonaceous chondrite clast indicate that it belongs to the CI-CM-CO clan; its volatile element abundances are intermediate between those of CM and CO chondrites. Abundances of nonvolatile elements in the silicate host are similar to those in the carbonaceous chondrite clast and in CM chondrites; the rare earths are unfractionated. We conclude that it is not achondritic as previously designated, but chondritic and that it is probably related to the CI-CM-CO clan; its volatile abundances are lower than those in CO chondrites. Oxygen isotope data are consistent with these classifications. Host metal in Bencubbin and in the closely related Weatherford meteorite has low abundances of moderately volatile siderophiles; among iron meteorite groups its nearest relative is group IIIF.We suggest that Bencubbin and Weatherford formed as a result of an impact event on a carbonaceous chondrite regolith. The impact generated an ‘instant magma’ that trapped and surrounded regolithic clasts to form the polymict breccia. The parent of this ‘magma’ was probably the regolith itself, perhaps mainly consisting of the so-called ‘enstatite’ chondrite materials. Accretion of such a variety of materials to a small parent body was probably only possible in the asteroid belt.     

Evidence linking coronal transients to the evolution of coronal holes

The positions of X-ray coronal transients outside of active regions observed during Skylab were superposed on H synoptic charts and coronal hole boundaries for seven solar rotations. We confirmed a detailed spatial association between the transients and neutral lines. We found that most of the transients were related to large-scale changes in coronal hole area and tended to occur on the borders of evolving equatorial holes.Skylab Solar Workshop Post-Doctoral Appointee, 1975–1977.     

Microscopic spectral features in solar decametric bursts and coronal irregularities

A crossed Yagi antenna array at 35 MHz was employed in conjunction with a polarization switch so as to enable spectral observations of solar noise storm activity in R and L polarizations. Intense decametric solar noise storms were recorded during the third week of November 1975 and fourth week of March 1976 with the help of a high resolution spectroscope operating near 35 MHz.The paper describes some of the new microscopic spectral features observed during these two noise storms. Three sets of high resolution dynamic spectra of decametric solar bursts, two of which are explained in terms of induced scattering of Langmuir waves by thermal ions and the third in terms of additional propagation effects through dense coronal irregularities, are presented. The microscopic bursts, classified as inverted U U and dots, represent small-scale (10⁴ km) phenomena with durations of less than a second.Some burst spectra appear as chain of dots with individual bandwidths 40 kHz and durations 0.3 sec. It is suggested that the bandwidth of such dot emissions (40 kHz) provides an evidence that they might indeed be generated by the process of induced scattering of plasma waves which predicts emission bandwidth f × 10^–3, where f is the center frequency.Some bursts are observed as a chain of striations showing curvature along the frequency axis which is attributed to dispersion in propagation delays through the dense coronal irregularities.     

Acoustic core logging in blast-damaged rock

Thill, R.E. and D' Andrea, D. V., 1975. Acoustic core logging in blast-damaged rock. Eng. Geol., 10: 13–36.The Bureau of Mines, in cooperation with the Duval Corp., conducted a blast-fragmentation experiment to determine the feasibility of preparing a porphyry copper-molybdenum deposit for in-situ leaching. The blast was designed with ten 9-inch-diameter blastholes to depths of 110 feet in an equilateral triangle configuration; spacings between blastholes were 15, 20, and 25 ft. One of the major problems in the experiment was in assessing blast damage. Acoustic core-logging equipment and methods were devised and used as one approach in solving this problem. Ultrasonic pulse travel-times were determined in four diametral directions at 2-ft intervals of depth to a final depth of 120 ft in three preblast and six postblast drill cores at the Duval test site. The acoustic logging program provided compressional wave travel-time at 0°, 45°, 90°, and 135° around the core circumference, maximum travel-time difference, mean compressional-wave velocity, and an anisotropy factor. Other acoustic parameters introduced in the analyses were stiffness modulus, seismic quality designation (SQD), and a compensated velocity to account for portions of the core that were nonrecoverable or too highly fractured to permit diametral travel-time measurements.The acoustic parameters all indicated the deterioration in structural quality from the preblast condition, in which the rock already was badly fractured and weathered, to the more highly fractured postblast condition. Because of the highly fragmented, poor structural condition of the rock after blasting, the rock was indicated to be suitable for in-situ leaching, at least at the 20- and 15-ft blasthole spacings, and even in some zones in the rock at the 25-ft blasthole spacing.     

Cyclotron wave instability in the corona and origin of solar radio emission with fine structure

The longitudinal waves (Bernstein modes and plasma waves near the hybrid frequency) in a mixture of equilibrium coronal plasma and a small group of energetic electrons are investigated. The energetic electrons have a nonequilibrium momentum distribution inherent in trapped particles. The frequency dependence of the cyclotron instability increments is studied. Attention is paid to a significant role of the relativistic effects for the cyclotron instability of longitudinal waves. For sufficiently large velocity of nonequilibrium electrons the increments are shown to increase when the hybrid frequency coincides with one of the gyrofrequency harmonics (double plasma resonance). The results obtained are used in Parts II and III to explain tadpoles and zebra-pattern in solar radio bursts.