Wet removal of highly soluble gases

Partition, not kinetics, ultimately determines the concentration of highly soluble gases in cloud droplets. Partition equations are formulated and applied to idealized air-mass thunderclouds and precipitating stratus. Contribution to aqueous concentrations from sub-cloud scavenging of highly soluble gases is estimated at between 10 and 20% under relatively unpolluted conditions. Data indicate that evaporation can produce enhancements in concentration of as much as a factor of 3. The calculations give large-scale mean coefficients of wet removal of highly soluble gases of about 2.8×10^-6 s^-1 (4-day residence time) for air-mass thunderclouds and precipitating stratus. Removal is so effective that the mean scale heights of these gases should be decreased to 2 km or less. The criterion of high solubility in this paper is that K ^H (Henry's Law coefficient) > 10⁵ mol l^-1 atm^-1. Gases that are effectively highly soluble include HCl, HNO₃, H₂SO₄, H₂O₂, NH₃ in acid droplets, SO₂ in oxidizing droplets (and probably some light amines and sulfonic acids), but not SO₂ in the absence of oxidants, nor HCHO. A variation of removal coefficient and scale height with solubility is presented. A comparison of atmospheric NH₃ concentrations deduced from rain NH₄ ⁺ and measured directly gives reasonable agreement.     

Oxidation states of the upper mantle recorded by megacryst ilmenite in kimberlite and type A and B spinel lherzolites

The intrinsic oxygen fugacities of homogeneous, inclusion-free, megacryst ilmenites from the Frank Smith, Excelsior, Sekameng and Mukorob kimberlite pipes in southern Africa, and the alnöitic breccia in the Solomon Islands have been determined. Similar measurements have been made of the type A and B spinel peridotites from San Carlos in Arizona. The type A peridotites are characterised by oxygen fugacities close to the iron-wüstite buffer, similar to those of equivalent peridotite specimens from other continental and island arc environments. In strong contrast, the type B peridotites and all of the ilmenite megacrysts range between the oxygen fugacities defined by the nickelnickel oxide and fayalite-magnetite-quartz buffers. A close relationship between type B peridotites, oxidized metasomatizing fluids in the upper mantle and oxidized, silicaundersaturated magma types is suggested. It is unlikely that a solid elemental carbon phase can be an equilibrium crystallization product of kimberlite magmas if the ilmenite megacrysts represent the redox state of kimberlite melts. The ultimate source of the oxidizing fluids and the development of such a wide dispersion (>4 orders of magnitude) in oxygen fugacities of the upper mantle is not clear, but may involve recycled lithosphere, fluids from the lower mantle or result from the relatively rapid diffusion of H₂, compared with other potential volatile species, in the mantle.     

Circumstellar disks and planetary formation

The role of circumstellar disks in star and planetary formation is briefly reviewed. The observed disk around MWC 349 is used as an example and a table of evolutionary time scales and parameters is presented. The disk about MWC 349 is characteristic of that expected about a massive star. Disk structure about solar mass stars is more completely reviewed by Cameron (1978). The parameters for the disk indicate that there is a deduced region where conditions are appropriate for dust condensation and possible aggregation of material to planetary masses. For the purposes of the discussion we are assuming that the infrared as well as optical radiation arises from the disk which extends the known extent of the disk to 10¹⁴cm. It is not yet certain that this is the case.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.     

Conjugate observations of the day-side reconnection electric field: A GEM boundary layer campaign

Data from HF-radars are used to make the first simultaneous conjugate measurements of the day-side reconnection electric field. A period of 4 h around local magnetic noon are studied during a geospace environment modeling (GEM) boundary layer campaign. The interplanetary magnetic field (IMF) was southward whilst the eastward component (By) was variable. The flow patterns derived from the radar data show the expected conjugate asymmetries associated with IMF |By| ≥ 0. High-time resolution data (50 and 100 s) enable the flow of plasma across the open/closed field line boundary (the separatrix) to be studied in greater detail than in previous work. The latitude of the separatrix follows the same general trend in both hemispheres but shows a hemispherical difference of 4°, with the summer cusp at higher latitude, as expected from dipole tilt considerations. However, the short-time scale motion of the separatrix cannot be satisfactorily resolved within the best resolution (300 m s⁻¹) of the experiment. The orientation of the separatrix with respect to magnetic latitude is found to follow the same trend in both hemispheres and qualitatively fits that predicted by a model auroral oval. It shows no correlation with IMF By. However, the degree of tilt in the Northern (summer) Hemisphere is found to be significantly greater than that given by the model oval. The convection pattern data show that the meridian at which throat flow occurs is different in the two hemispheres and is controlled by IMF By, in agreement with empirically derived convection patterns and theoretical models. The day-side reconnection electric field values are largest when the radar’s meridian is in the throat flow or early afternoon flow regions. In the morning or afternoon convection cells, the reconnection electric field tends to zero away from the throat flow region. The reconnection electric field observed in the throat flow region is bursty in nature.     

Diatom biostratigraphy of tsunami deposits: Examples from the 1998 Papua New Guinea tsunami

Distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment. Sediments associated with the 1998 tsunami that destroyed much of the Sissano lagoon area in northern Papua New Guinea have been investigated. Surface sediments from three transects across the sediment spit near Warapu have been examined for diatom content and preservation. The preservation is variable, and the data show an, often chaotic, assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash. The diatoms identified within the Warapu sediments indicate an origin from within the inter-tidal and offshore area rather than from the beach–sand spit complex. The sand deposits disclose a high percentage, in excess of 75%, of broken diatom valves, and a predominance of centric (circular) species due to preferential preservation. The study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo-tsunami deposits.     

The representer method for two-phase flow in porous media

The representer method is applied to a one-dimensional two-phase flow model in porous media; capillary pressure and gravity are neglected. The Euler–Lagrange equations must be linearized, and one such linearization is presented here. The representer method is applied to the linear system iteratively until convergence, though a rigorous proof of convergence is out of reach. The linearization chosen is easy to calculate but does not converge for certain weights; however, a simple damping restores convergence at the cost of extra iterations. Numerical experiments are performed that illustrate the method, and quick comparison to the ensemble Kalman smoother is made. This research was supported by NSF grant EIA-0121523.     

Galaxy Evolution in the Northern HDF

The history of star formation in the Northern Hubble Deep Field is probed using a combination of optical and near infrared images taken with WFPC2 and NICMOS on the Hubble Space Telescope. These images cover more than a factor of five in wavelength. This broad wavelength coverage allows accurate photometric determinations of redshift, extinction and intrinsic spectral energy distribution for each galaxy. From these parameters the star formation rate for each galaxy is determined by relating the 1500 angstrom flux to the net star formation rate. We then correct the rates at high redshift for the effects of surface brightness dimming by using a standard form of the star formation intensity distribution. Our measurements show that the star formation rate in the Northern HDF is roughly constant from a redshift of 1 through 6. This revised version was published online in September 2006 with corrections to the Cover Date.