Titan trace gaseous composition from CIRS at the end of the Cassini-Huygens prime mission     

A. Coustenis  D.E. Jennings  R.K. Achterberg  S. Vinatier  N.A. Teanby  R.C. Carlson  G. Bampasidis  P.N. Romani 《Icarus》2010,207(1):461-18

This paper reports on the results from an extensive study of all nadir-looking spectra acquired by Cassini/CIRS during the 44 flybys performed in the course of the nominal mission (2004-2008). With respect to the previous study (Coustenis, A., and 24 colleagues [2007]. Icarus 189, 35-62, on flybys TB-T10) we present here a significantly richer dataset with, in particular, more data at high northern and southern latitudes so that the abundances inferred here at these regions are more reliable. Our enhanced high-resolution dataset allows us to infer more precisely the chemical composition of Titan all over the disk. We also include improved spectroscopic data for some molecules and updated temperature profiles. The latitudinal distributions of all of the gaseous species are inferred. We furthermore test vertical distributions essentially for acetylene (C₂H₂) from CIRS limb-inferred data and from current General Circulation Models for Titan and compare our results on all the gaseous abundances with predictions from 1-D photochemical-radiative models to check the reliability of the chemical reactions and pathways.  相似文献   

Abundances of Jupiter's trace hydrocarbons from Voyager and Cassini     

C.A. Nixon  R.K. Achterberg  P.N. Romani  X. Zhang  P.G.J. Irwin 《Planetary and Space Science》2010,58(13):1667-1680

The flybys of Jupiter by the Voyager spacecraft in 1979, and over two decades later by Cassini in 2000, have provided us with unique datasets from two different epochs, allowing the investigation of seasonal change in the atmosphere. In this paper we model zonal averages of thermal infrared spectra from the two instruments, Voyager 1 IRIS and Cassini CIRS, to retrieve the vertical and meridional profiles of temperature, and the abundances of the two minor hydrocarbons, acetylene (C₂H₂) and ethane (C₂H₆). The spatial variation of these gases is controlled by both chemistry and dynamics, and therefore their observed distribution gives us an insight into both processes. We find that the two gases paint quite different pictures of seasonal change. Whilst the 2-D cross-section of C₂H₆ abundance is slightly increased and more symmetric in 2000 (northern summer solstice) compared to 1979 (northern fall equinox), the major trend of equator to pole increase remains. For C₂H₂ on the other hand, the Voyager epoch exhibits almost no latitudinal variation, whilst the Cassini era shows a marked decrease polewards in both hemispheres. At the present time, these experimental findings are in advance of interpretation, as there are no published models of 2-D Jovian seasonal chemical variation available for comparison.  相似文献   

Heuristic Approach for Renovating a Monitoring Network Measuring Sea Water Intrusion into the Coastal Aquifer     

Abraham J. Melloul  Shmuel Aberbach 《Ground Water Monitoring & Remediation》2007,27(2):119-128

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Direct feeding of the black hole at the Galactic Centre with radial gas streams from close-in stellar winds     

Abraham Loeb 《Monthly notices of the Royal Astronomical Society》2004,350(2):725-728

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Reverberation envelope statistics and their dependence on sonar bandwidth and scattering patch size     

Abraham  D.A. Lyons  A.P. 《Oceanic Engineering, IEEE Journal of》2004,29(1):126-137

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Simulation of non-Rayleigh reverberation and clutter     

Abraham  D.A. Lyons  A.P. 《Oceanic Engineering, IEEE Journal of》2004,29(2):347-362

The simulation of active sonar reverberation time series has traditionally been done using either a computationally intensive point-scatterer model or a Rayleigh-distributed reverberation-envelope model with a time-varying power level. Although adequate in scenarios where reverberation arises from a multitude of scatterers, the Rayleigh model is not representative of the target-like non-Rayleigh reverberation or clutter commonly observed with modern high-resolution sonar systems operating in shallow-water environments. In this paper, techniques for simulating non-Rayleigh reverberation are developed within the context of the finite-number-of-scatterers representation of K-distributed reverberation, which allows control of the reverberation-envelope statistics as a function of system (beamwidth and bandwidth) and environmental (scatterer density and size) parameters. To avoid the high computational effort of the point-scatterer model, reverberation is simulated at the output of the matched filter and is generated using efficient approximate methods for forming K-distributed random variables. Finite impulse response filters are used to introduce the effects of multipath propagation and the shape of the reverberation power spectrum, the latter of which requires the development of a prewarping of the K distribution parameters to control the reverberation-envelope statistics. The simulation methods presented in this paper will be useful in the testing and evaluation of active sonar signal processing algorithms, as well as for simulation-based research on the effects of the sonar system and environment on the reverberation-envelope probability density function.  相似文献   

shinyNORRRM: A Cross-Platform Software to Calculate the CIPW Norm     

González-Guzmán  Reneé  Elizondo-Pacheco  Luis Alejandro  González-Roque  Abraham  Sánchez-Torres  Carlos Eduardo  Cárdenas-Muñoz  Kevin Samuel 《Mathematical Geosciences》2023,55(4):563-577

In this paper, a novelty-free software to assess an efficient CIPW Norm (± 0.006 wt.% in differences between input and output data) is presented. The package is available in the official repository for user-contributed R packages (CRAN: Comprehensive R Archive Network). The software is able to handle big data sets and considers minor and trace element compositions. The algorithm can calculate odd minerals in igneous rocks, such as cancrinite and calcite, adjust the Fe⁺³/Fe⁺² ratio in different standard approaches, and recalculate the compositions of the rocks in an anhydrous basis (100 ± 0.003 wt.% volatile-free adjusted). Furthermore, the package calculates several petrological parameters, and the graphical outputs are displayed following IUGS scheme standards. The prime aspect of shinyNORRRM is the symbiosis of native R functions with the R package’s shiny (Web Application Framework for R) to run the norm in a user-friendly interface. shinyNORRRM can be executed in any operating system and requires no previous programming knowledge, thus promising to be the universal computational program in this matter. The output data are printed in the standard comma-separated values (*.csv) format, which is highly compatible with general spreadsheet editors. In this work, the algorithm of our program is validated using already compiled whole-rock geochemical databases.

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Cassini CIRS retrievals of ammonia in Jupiter's upper troposphere     

Richard K. Achterberg  Barney J. Conrath 《Icarus》2006,182(1):169-180

The zonal mean ammonia abundance on Jupiter between the 400- and 500-mbar pressure levels is inferred as a function of latitude from Cassini Composite Infrared Spectrometer data. Near the Great Red Spot, the ammonia abundance is mapped as a function of latitude and longitude. The Equatorial Zone is rich in ammonia, with a relative humidity near unity. The North and South Equatorial Belts are depleted relative to the Equatorial Zone by an order of magnitude. The Great Red Spot shows a local maximum in the ammonia abundance. Ammonia abundance is highly correlated with temperature perturbations at the same altitude. Under the assumption that anomalies in ammonia and temperature are both perturbed from equilibrium by vertical motion, we find that the adjustment time constant for ammonia equilibration is about one third of the radiative time constant.  相似文献   

CO<Subscript>2</Subscript> Air–Sea Exchange due to Calcium Carbonate and Organic Matter Storage,and its Implications for the Global Carbon Cycle     

Abraham?LermanEmail author  Fred?T.?Mackenzie 《Aquatic Geochemistry》2005,11(4):345-390

Release of CO₂ from surface ocean water owing to precipitation of CaCO₃ and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a quotient θ = (CO₂ flux to the atmosphere)/(CaCO₃ precipitated). θ depends not only on water temperature and atmospheric CO₂ concentration but also on the CaCO₃ and organic carbon masses formed. In CO₂ generation by CaCO₃ precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric CO₂ concentration (195–375 ppmv), and increasing CaCO₃ precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic carbon counteracts the CO₂ production by carbonate precipitation and it results in lower CO₂ emissions from the surface layer. When atmospheric CO₂ increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO₂ transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric CO₂. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon from land, the calculated CO₂ flux to the atmosphere is a function of the CaCO₃ and C_org net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO₂ flux near the Last Glacial Maximum is 17 to 7×10¹² mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time it is 38–42×10¹² mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic emissions of CO₂ to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total alkalinity owing to the CaCO₃ storage and consequent emission of CO₂. These results are in agreement with the conclusions of a number of other investigators. As the CO₂ uptake in mineral weathering is a major flux in the global carbon cycle, the CO₂ weathering pathway that originates in the CO₂ produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large imbalances of the atmosphere and land organic reservoir at 10²–10⁴-year time scales.  相似文献   

Electrical resistance sensors record spring flow timing, Grand Canyon, Arizona     

Adams EA  Monroe SA  Springer AE  Blasch KW  Bills DJ 《Ground water》2006,44(5):630-641

Springs along the south rim of the Grand Canyon, Arizona, are important ecological and cultural resources in Grand Canyon National Park and are discharge points for regional and local aquifers of the Coconino Plateau. This study evaluated the applicability of electrical resistance (ER) sensors for measuring diffuse, low-stage (<1.0 cm) intermittent and ephemeral flow in the steep, rocky spring-fed tributaries of the south rim. ER sensors were used to conduct a baseline survey of spring flow timing at eight sites in three spring-fed tributaries in Grand Canyon. Sensors were attached to a nearly vertical rock wall at a spring outlet and were installed in alluvial and bedrock channels. Spring flow timing data inferred by the ER sensors were consistent with observations during site visits, with flow events recorded with collocated streamflow gauging stations and with local precipitation gauges. ER sensors were able to distinguish the presence of flow along nearly vertical rock surfaces with flow depths between 0.3 and 1.0 cm. Laboratory experiments confirmed the ability of the sensors to monitor the timing of diffuse flow on impervious surfaces. A comparison of flow patterns along the stream reaches and at springs identified the timing and location of perennial and intermittent flow, and periods of increased evapotranspiration.  相似文献