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1.
A time-dependent microphysical model is used to study the evolution of ethane ice clouds in Titan’s atmosphere. The model simulates nucleation, condensational growth, evaporation, coagulation, and transport of particles. For a critical saturation of 1.15 (a lower limit, determined by laboratory experiments), we find that ethane clouds can be sustained between altitudes of 8 and 50 km. Growth due to coalescence is inefficient, limiting the peak in the size distribution (by number) to 10 μm. These clouds vary with a period of about 20 days. This periodicity disappears for higher critical saturation values where clouds remain subvisible. Rainout of ethane due to methane cloud formation raises the altitude of the ethane cloud bottom to near the tropopause and may eliminate ethane clouds entirely if methane cloud formation occurs up to 30 km. However, clouds formed above the troposphere from other gases in Titan’s atmosphere could be sustained even with rainout up to 30 km. Although the optical depth of ethane clouds above 20 km is typically low, short-lived clouds with optical depths of order 0.1-1 can be created sporadically by dynamically driven atmospheric cooling. Ethane cloud particles larger than 25 μm can fall to the surface before total evaporation. However, ethane clouds remain only a small sink for tholin particles. At the peak of their cycle, the optical depth of ethane clouds could be comparable to that of tholin in the near-infrared, resulting in a 5% increase in Titan’s albedo for wavelengths between 1 and 2 μm. A number of factors limit our ablility to predict the ethane cloud properties. These factors include the mixing time in the troposphere, the critical saturation ratio for ethane ice, the existence of a surface reservoir of ethane, the magnitude and timing of dynamically driven temperature perturbations, and the abundance and life cycle of methane clouds. 相似文献
2.
A primitive equation model and a statistical predictor are coupled by data assimilation in order to combine the strength of both approaches. In this work, the system of two-way nested models centred in the Ligurian Sea and the satellite-based ocean forecasting (SOFT) system predicting the sea surface temperature (SST) are used. The data assimilation scheme is a simplified reduced order Kalman filter based on a constant error space. The assimilation of predicted SST improves the forecast of the hydrodynamic model compared to the forecast obtained by assimilating past SST observations used by the statistical predictor. This study shows that the SST of the SOFT predictor can be used to correct atmospheric heat fluxes. Traditionally this is done by relaxing the model SST towards the climatological SST. Therefore, the assimilation of SOFT SST and climatological SST are also compared. 相似文献
3.
Boron isotope variations in nature: a synthesis 总被引:9,自引:0,他引:9
S. Barth 《International Journal of Earth Sciences》1993,82(4):640-651
The large relative mass difference between the two stable isotopes of boron, 10B and 11B, and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes. Published 11B values (relative to the NBS SRM-951 standard) span a wide range of 90. The lowest 11B values around — 30 are reported for non-marine evaporite minerals and certain tourmalines. The most 11B-enriched reservoir known to date are brines from Australian salt lakes and the Dead Sea of Israel with 11B values up to +59. Dissolved boron in present-day seawater has a constant world-wide 11B value of + 39.5. In this paper, available 11B data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects, including possible tracer applications of boron-isotope geochemistry, are summarized.
Résumé La grande différence relative de masse entre les isotopes stables du bore, 10B et 11B, et la grande réactivité geochimique du bore ont pour conséquence un fractionnement isotopique naturel important. Les valeurs de 11B publiées (par rapport au standard NBS SRM-951) varient de 90. Les valeurs de 11B les plus basses (–30) correspondent aux evaporites non-marines et à certaines tourmalines. Le réservoir le plus enrichi en 11B est représenté par les saumures des lacs salés d' Australie et par la Mer Morte en Israël, qui ont des valuers de 11B allent jusqu'à + 59. L'eau de mer a une valeur de 11B mondialement constante de + 39.5. Des valeurs de 11B des solutions naturelles ainsi que des roches et minéraux de différentes origines, publiées jusqu'à présent, sont présentées ici. En outre quelques aspects importants concernant la géochimie des isotopes du bore y compris quelques applications sont exposés.相似文献
4.
The vertical distribution of ozone in the atmosphere of Mars is computed from ultraviolet spectra obtained by the Mariner 9 spacecraft. In the Northern Hemisphere the ozone scale height is much smaller than the atmospheric scale height in midlatitudes and increases rapidly to a maximum farther north. At high latitudes (above 60°) there is no significant difference between the scale heights of ozone in the Northern (winter) Hemisphere and the Southern (summer) Hemisphere. Comparison of the ozone distribution with atmospheric temperature structure indicates that at some locations in the North, the density of water vapor increases with altitude, and the time for vertical mixing is about 3 days or more. 相似文献
5.
6.
Eric Barthélemy 《Surveys in Geophysics》2004,25(3-4):315-337
Ocean waves entering the near-shore zone undergo nonlinear and dispersive processes. This paper reviews nonlinear models, focusing on the so-called Serre equations. Techniques to overcome their limitations with respect to the phase speed are presented. Nonlinear behaviours are compared with theoretical results concerning the properties of Stokes waves. In addition, the models are tested against experiments concerning periodic wave transformation over a bar topography and of the shoaling of solitary waves on a beach. 相似文献
7.
Tom R. Robinson Tim R. H. Davies Thomas M. Wilson Caroline Orchiston Nicolas Barth 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(2):146-163
Coseismic landsliding presents a major hazard to infrastructure in mountains during large earthquakes. This is particularly true for road networks, as historically coseismic landsliding has resulted in road losses larger than those due to ground shaking. Assessing the exposure of current and planned highway links to coseismic landsliding for future earthquake scenarios is therefore vital for disaster risk reduction. This study presents a method to evaluate the exposure of critical infrastructure to landsliding from scenario earthquakes from an underlying quantitative landslide hazard assessment. The method is applied to a proposed new highway link in South Island, New Zealand, for a scenario Alpine Fault earthquake and compared to the current network. Exposure (the likelihood of a network being affected by one or more landslides) is evaluated from a regional-scale coseismic landslide hazard model and assessed on a relative basis from 0 to 1. The results show that the proposed Haast-Hollyford Highway (HHH) would be highly exposed to coseismic landsliding with at least 30–40?km likely to be badly affected (the Simonin Pass route being the worse affected of the two routes). In the current South Island State Highway network, the HHH would be the link most exposed to landsliding and would increase the total network exposure by 50–70% despite increasing the total road length by just 3%. The present work is intended to provide an effective method to assess coseismic landslide hazard of infrastructure in mountains with seismic hazard, and potentially identify mitigation options and critical network segments. 相似文献
8.
Due to a particularly favourable geologic and tectonic setting in the Eastern Province, Saudi Arabia has the world largest oil reserves and is the third largest oil-producing nation in the world. Based on oil and gas revenues, the Kingdom experienced an overwhelming development during the last few decades, changing a desert country into a modern industrialized nation. Main characteristics of spatial changes are based on processes of urbanization and industrialization, on agricultural reclamations and infra-structural developments. Since the natural environment of deserts and semi-deserts in the Eastern Province is determined by an extremely sensitive equilibrium, environmental impacts, shortages in water resources, as well as limited human resources are causing basic problems, which will influence future developments. 相似文献
9.
There is an exceptionally rich aquatic fauna in the epikarst, the skin of karst. High species richness in the epikarst, coupled
with its special vulnerability as the first point of entry of nearly all toxic spills, makes its protection especially important.
The epikarst fauna may also be an useful tool in tracing the potential route of pollutants. Copepods in epikarst have extremely
local distributions, and their body size is such that they are largely at the mercy of directional flows. In a series of caves
in southwest Slovenia and West Virginia, a significant fraction of the copepod species occur in less than 100 m of linear
extent. This suggests a pattern of highly restricted lateral flow under normal conditions and the distribution of copepods
could potentially be used to trace water movement. Under high flow conditions as would often be the case with toxic spill,
mounding of water may increase the lateral radius of flow. Nevertheless, copepods may be useful tracers. 相似文献
10.
F. Böttcher St. Barth J. Peinke 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(3):299-308
Atmospheric wind speeds and their fluctuations at different locations (onshore and offshore) are examined. One of the most striking features is the marked intermittency of probability density functions (PDF) of velocity differences, no matter what location is considered. The shape of these PDFs is found to be robust over a wide range of scales which seems to contradict the mathematical concept of stability where a Gaussian distribution should be the limiting one. Motivated by the non-stationarity of atmospheric winds it is shown that the intermittent distributions can be understood as a superposition of different subsets of isotropic turbulence. Thus we suggest a simple stochastic model to reproduce the measured statistics of wind speed fluctuations. 相似文献