Evolution of cool skin and direct air-sea gas transfer coefficient during daytime     

Alexander V. Soloviev  Peter Schlüssel 《Boundary-Layer Meteorology》1996,77(1):45-68

Absorption of solar radiation within the thermal molecular sublayer of the ocean can modify the temperature difference across the cool skin as well as the air-sea gas transfer. Our model of renewal type is based on the assumption that the thermal and diffusive molecular sublayers below the ocean surface undergo cyclic growth and destruction, the heat and gas transfer between the successive burst events are performed by molecular diffusion. The model has been upgraded to include heating due to solar radiation. The renewal time is parameterized as a function of the surface Richardson number and the Keulegan number. A Rayleigh number criterion characterizes the convective instability of the cool skin under solar heating. Under low wind speed conditions, the solar heating can damp the convective instability, strongly increasing the renewal time and correspondingly decreasing the interfacial gas exchange. In the ocean, an additional convective instability caused by salinity flux due to evaporation becomes of importance in such cases. The new parameterization is compared with the cool skin data obtained in the western equatorial Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment in February 1993. In combination with a model of the diurnal thermocline it describes main features of the field data both in nighttime and daytime. Under low wind speed conditions (< 5 m s^-1) diurnal variations of the sea surface temperature due to the formation of a diurnal thermocline were substantially larger than those across the cool skin. Under wind speeds > 5 m s^-1, diurnal variations of the surface temperature due to the variations of the thermal molecular sublayer become more important.  相似文献   

About the specification of erosion flux for soft stratified cohesive sediments     

Georges Chapalain  Y. Peter Sheng  André T. Temperville 《Mathematical Geology》1994,26(6):651-676

The present paper deals with the specification of bed erosion flux that accounts for the effects of sediment-induced stratification in the water column. Owing to difficulties in measuring the bed shear stress _b and the erosive shear strength _s, we suggest a series of methods that combine laboratory and numerical experiments. A simplified turbulent transport model that includes these effects helps to quantify _b and _s. Focusing on soft stratified beds, the present study considers erosion rate formulas of the form =_f exp {[T_b-T_s]} where is a model constant (=1 for Gularte's (1978) formula and =1/2 for Parchure's (1984) formula). First, the bed erosive strength profile _s(Z) is adjusted by forcing the turbulent transport model with measured erosion rates. Second, three procedures are suggested to determine the erosion rate formula coefficients _f and : a global procedure and two different layer-by-layer procedures. Each procedure is applied to an erosion experiment conducted in a rotating annular flume by Villaret and Paulic (1986). The use of the layer-by-layer procedure based on a least squares fitting technique provides a closer fit than the global procedure. The present study points out the complementarity of experimental and numerical approaches and also suggests possible improvements in laboratory test procedures.  相似文献   

Simco,a simulation software for CONICA,the coude nir camera for the very large telescope     

Peter Claes 《Experimental Astronomy》1994,3(1-4):121-122

CONICA is an acronym for COudé Near Infrared Camera. It is one of the four currently planned Infrared instruments for ESO's Very Large Telescope (VLT) in Chile. This multimode instrument is to be installed at the Coudé-focus (of Unit Telescope no. 1), where adaptive optics and speckle interferometry will also be available. High angular resolution imaging (to the diffraction limit) will be possible in the 1–5 m range, as well as spectroscopy with low- and medium resolution and polarimetry by means of Wollaston prism and wiregrid analysers. Various softwares are developed for this instrument. One of them: the Simulation Software has a threefold aim: 1. provide the user with feedback information on his/her choices of observational parameters. This is be achieved by displaying the calculated performance and throughput of the combined Source-Atmosphere-Telescope-Camera-Detector system in various formats, such as images, tables, isophotical images ... for point as well as for extended sources (also annular, double, etc.); 2. verify if his expectations are realistic, before actually using CONICA itself. 3. give feedback on the design to the developers of the instrument.On leave from his original institute, now at ESTEC in the ISO-project  相似文献   

The “Zero-order Model” revisited: Paul Schindler's influence on the development of trace metal scavenging models     

Santschi  Peter H.  Honeyman  Bruce D.  Quigley  Matthew S. 《Aquatic Sciences - Research Across Boundaries》1993,55(4):230-239

In 1975 Paul Schindler produced the first oceanic trace metal scavenging model to explicitly include the role of surface chemistry as a control on trace metal water column residence times. The eighteen years that have elapsed since the publication of Schindler's seminal paper have seen the development of a variety of oceanic scavenging models; yet, the fundamental insight of his Zero-order Model remains the benchmark. This paper describes the role of Paul Schindler's work on surface chemistry in providing a framework for the current generation of trace element scavenging models.  相似文献   

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic     

Josef Vesely  Heather Almquist-Jacobson  Lisa M. Miller  Stephen A. Norton  Peter Appleby  Aruna S. Dixit  John P. Smol 《Journal of Paleolimnology》1993,8(3):211-231

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.  相似文献   

Genesis of high Mg# andesites and the continental crust   总被引：38，自引：2，他引：36  

Peter B. Kelemen 《Contributions to Mineralogy and Petrology》1995,120(1):1-19

The continental crust has an andesitic composition with high Mg/(Mg+Fe) and Ni contents which may be too high to have formed by differentiation of basaltic magmas. Instead, mantle-derived, high Mg# andesites (HMA) may form a substantial component of the crust. HMA may be produced by partial melting of previously depleted, subsequently metasomatised mantle peridotite. However, they are more likely produced by reaction between ascending melts and mantle peridotite. HMA are less common than basalts among lavas in modern island arcs, but may have been more common in the past, may be produced in specific environments (such as ridge subduction), may be more common among plutonic rocks in the lower and middle crust than among lavas at the surface, and may be selectively preserved during later erosion and subduction processes.  相似文献   

Is C/O enhanced in NGC 253?     

Andrew Harrison  Peter Brand  Adrian Russell  Phil Puxley 《Astrophysics and Space Science》1995,224(1-2):473-474

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.  相似文献   

Baroclinic instabilities in Jupiter's zonal flow     

Peter J. Gierasch  Andrew P. Ingersoll  David Pollard 《Icarus》1979,40(2):205-212

The baroclinic stability of Jupiter's zonal flow is investigated using a model consisting of two continuously stratified fluid layers. The upper layer, containing a zonal shear flow and representing the Jovian cloudy regions above p ～ 5 bars, is the same as Eady's (1949) model for the Earth. The lower layer has a relatively large but finite depth with a quiescent basic state, representing the deep Jovian fluid bulk below p ～ 5 bars. Due to the presence of the lower layer, the linearized non-dimensional growth rates are drastically reduced from the O(1) growth rates of the original Early model. Only very long wavelengths relative to the upper fluid's radius of deformation L₁ are unstable. Eddy transports of heat are also reduced relative to estimates based on scaling arguments alone. Since the hydrostatic approximation for the lower-layer perturbation breaks down at great depths, a second model is presented in which energy propagates downward in an infinitely deep lower fluid obeying the full linearized fluid equations. In this model, the growth rates are again very small, but now all wavelengths are unstable with maximum growth rates occurring for wavelengths O(1) relative to L₁. These results illustrate the importance for the upper-layer meteorology of the interface boundary condition with the lower fluid, which is radically different from the rigid lower boundary of the Earth's troposphere.  相似文献   

Close binary systems before and after mass transfer: A comparison of observations and theory     

J. P. De Grève  D. Vanbeveren 《Astrophysics and Space Science》1980,68(2):433-457

From a search through the literature 174 close binaries with known absolute dimensions have been sampled. Distinction is made between systems before and after mass exchange. Mass, period and mass ratio distributions and relations of the group of unevolved binaries (i.e., prior to mass exchange) are transformed into corresponding distributions and relations of evolved binaries. The transformations are based upon theM _1f=g(M _1f) relation derived from an extended set of published theoretical computations of the evolution of close binaries. From this relation the following characteristics of the system after mass exchange are computed:M _1f,M _2f (andq _f),P _f. Five different modes of mass transfer were applied for the computation of the values ofP _f andM _2f. The variation of the period was calculated using the formalism given by Vanbeverenet al. (1979). The results are compared to the observations of binary systems after mass exchange, and are discussed together with an analysis of the effect of several selection effects present in the distributions. The main conclusion is that, during mass exchange in close binaries, more than 50% of the mass is lost to the system in the process of transfer, removing a large amount of angular momentum.This research is supported by the National Foundation of Collective Fundamental Research of Belgium (F.K.F.O.) under No. 2.9009.79.  相似文献   

A model of the origin of the Jovian ring     

E. Grün  G. Morfill  G. Schwehm  T.V. Johnson 《Icarus》1980,44(2):326-338

Starting with the assumption that the micron-sized particles which make up the bright Jovian ring are fragments of erosive collisions between micrometeoroid projectiles and large parent bodies, a physical model of the ring is calculated. The physics of high-velocity impacts leads to a well-defined size distribution for the ejecta, the optical properties of which can be compared with observation. This gives information on the ejecta material (very likely silicates) and on the maximum size of the projectiles, which turns out to be about 0.1 μm. The origin of these projectiles is discussed, and it is concluded that dust particles ejected in volcanic activity from Io are the most likely source. The impact model leads quite naturally to a distribution in ejecta sizes, which in turn determines the structure of the ring. The largest ejecta form the bright ring, medium-sized ejecta form a disk extending all the way to the Jovian atmosphere, and the small ejecta form a faint halo, the structure of which is dominated by electromagnetic forces. In addition to the Io particles, interaction with interplanetary micrometeoroids is also considered. It is concluded that μm-sized ejecta from this source have ejection velocities which are several orders of magnitude too large, and thus cannot contribute significantly to the observed bright ring. However, the total mass ejection rate is significant. Destruction of these ejecta by the Io particles may provide additional particles for the halo.  相似文献