Heat exchange between water and ice in the Arctic Ocean     

Robert Alan Lake 《Meteorology and Atmospheric Physics》1967,16(2-3):242-259

Summary The heat balance equation for the bottom surface of floating sea ice is evaluated on the basis of observations of ice temperature, water temperature, current velocity, and ablation or accretion of ice. Assuming equality of the eddy diffusivities for momentum, heat, and salt (average 24 cm² sec^–1) it is shown that the temperature gradient in the oceanic boundary layer is extremely small (averages between 2.10^–5 and 4.10^–4°C/meter) and difficult to measure directly. It is suggested that a large part of the heat transfer from the relatively warm Atlantic water to the arctic atmosphere may occur through open leads in the ice cover.

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Zusammenfassung Die Wärmebilanzgleichung für die Unterseite von schwimmendem Meereis wird an Hand von Beobachtungen der Eistemperatur, der Wassertemperatur, der Strömungsgeschwindigkeit und der Eisdickenänderung ausgewertet. Unter der Annahme gleicher Austauschkoeffizienten für Bewegungsgröße, Wärme und Salzgehalt (im Mittel 24 cm² sec^–1) ergibt sich für die ozeanische Grenzschicht ein außerordentlich kleiner Gradient der Wassertemperatur (durchschnittlich zwischen 2.10^–5 und 4.10^–4°C/Meter), der durch direkte Beobachtungen schwer nachzuweisen ist. Es ist zu vermuten, daß ein beträchtlicher Teil der Wärmeabgabe von der relativ warmen atlantischen Wassermasse an die arktische Atmosphäre durch Öffnungen in der Meereisdecke erfolgt.

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Résumé On établit l'équation du bilan thermique valable pour la surface inférieure de la glace marine dérivante. Pour ce faire, on se sert d'observations de la température de la glace, de celle de l'eau, de la vitesse du courant et des variations de l'épaisseur de la glace. En admettant que les coefficients d'échange sont les mêmes pour la quantité de mouvement, la chaleur et le taux de salinité (en moyenne 24 cm² sec^–1), il résulte pour la couche limite un gradient extrêmement faible de la température de l'eau (situé en moyenne entre 2·10^–5 et 4·10^–4°C/m); un tel gradient est difficile à prouver au moyen d'observations directes. On peut supposer qu'une partie importante de la chaleur transmise par l'eau relativement chaude de l'Atlantique à l'atmosphère arctique passe au travers des lacunes de la couche de glace recouvrant l'océan.

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With 4 Figures

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Contribution 141, Department of Atmospheric Sciences, University of Washington, Seattle. This is a thesis submitted by the author in partial fulfillment of the requirements for the degree of Master of Science.  相似文献   

Scaling analysis of deposition from turbidity currents   总被引：3，自引：0，他引：3  

L.?Srivatsan  Larry?W.?Lake  Roger?T.?BonnecazeEmail author 《Geo-Marine Letters》2004,24(2):63-74

Many oil-bearing sedimentary deposits are formed by the settling of particles from turbidity currents. Modeling sedimentary processes that form these turbidites enables the calculation of properties such as extent, depth, porosity and permeability of hydrocarbon-bearing reservoirs. This paper estimates the extent and thickness of turbidites from the initial conditions of the turbidity flow. This is achieved by the application of scaling analysis of the partial differential equations that govern the dynamics of and deposition from turbidity currents. We apply the results of scaling analysis to five modern submarine fans. The predicted and actual values of the dimensions of the fan deposits match well. We then compare the derived results against tabulated sizes of ancient turbidites. The comparisons are good as long as we correctly identify the flow regimes in which the deposition took place. The good agreements observed in the two cases show that the estimates obtained using scaling analysis can provide useful first-guess values for the dimensions of the deposits.  相似文献   

Characterizing heterogeneous permeable media with spatial statistics and tracer data using sequential simulated annealing     

Akhil Datta-Gupta  Larry W. Lake  Gary A. Pope 《Mathematical Geology》1995,27(6):763-787

Characterizing heterogeneous permeable media using flow and transport data typically requires solution of an inverse problem. Such inverse problems are intensive computationally and may involve iterative procedures requiring many forward simulations of the flow and transport problem. Previous attempts have been limited mostly to flow data such as pressure transient (interference) tests using multiple observation wells. This paper discusses an approach to generating stochastic permeability fields conditioned to geologic data in the form of a vertical variogram derived from cores and logs as well as fluid flow and transport data, such as tracer concentration history, by sequential application of simulated annealing (SA). Thus, the method incorporates elements of geostatistics within the framework of inverse modeling. For tracer-transport calculations, we have used a semianalytic transit-time algorithm which is fast, accurate, and free of numerical dispersion. For steady velocity fields, we introduce a transit-time function which demonstrates the relative importance of data from different sources. The approach is illustrated by application to a set of spatial permeability measurements and tracer data from an experiment in the Antolini Sandstone, an eolian outcrop from northern Arizona. The results clearly reveal the importance of tracer data in reproducing the correlated features (channels) of the permeability field and the scale effects of heterogeneity.  相似文献   

Flexible spectral methods for the generation of random fields with power-law semivariograms     

Johannes Bruining  Diederik van Batenburg  Larry W. Lake  An Ping Yang 《Mathematical Geology》1997,29(6):823-848

Random field generators serve as a tool to model heterogeneous media for applications in hydrocarbon recovery and groundwater flow. Random fields with a power-law variogram structure, also termed fractional Brownian motion (fBm) fields, are of interest to study scale dependent heterogeneity effects on one-phase and two-phase flow. We show that such fields generated by the spectral method and the Inverse Fast Fourier Transform (IFFT) have an incorrect variogram structure and variance. To illustrate this we derive the prefactor of the fBm spectral density function, which is required to generate the fBm fields. We propose a new method to generate fBm fields that introduces weighting functions into the spectral method. It leads to a flexible and efficient algorithm. The flexibility permits an optimal choice of summation points (that is points in frequency space at which the weighting function is calculated) specific for the autocovariance structure of the field. As an illustration of the method, comparisons between estimated and expected statistics of fields with an exponential variogram and of fBm fields are presented. For power-law semivariograms, the proposed spectral method with a cylindrical distribution of the summation points gives optimal results.  相似文献   

华北克拉通南缘中条山-嵩山地区1.78Ga基性岩墙群的地球化学特征及构造环境   总被引：8，自引：6，他引：2  

胡国辉  胡俊良  陈伟  赵太平 《岩石学报》2010,26(5):1563-1576

幔源岩浆侵位产生的基性岩墙群是地壳伸展裂解的重要标志。华北克拉通南缘中条山-嵩山地区出露有大量的中元古代基性岩墙群,对其研究将有助于深入了解华北克拉通中元古代构造演化特征。其岩石类型以辉绿岩为主,少量辉长辉绿岩和辉绿玢岩;主要造岩矿物为斜长石和单斜辉石,其它矿物包括角闪石、Fe-Ti氧化物、磷灰石、黑云母、碱性长石和石英。锆石SHRIMPU-Pb年龄为1785±18Ma,代表岩墙的结晶年龄。岩石K2O+Na2O含量为3.63%～6.18%,K2O/Na2O比值为0.73～1.38,FeOT含量较高(10.03%～13.59%),属于拉斑玄武岩系列。岩石的稀土元素含量高(142×10-6～381×10-6),亏损Nb、Ta、Zr、Hf等高场强元素,富集Rb、Ba、La等大离子亲石元素,全岩εNd(t)值为-6.2～-8.1。岩墙的固结指数(SI)和MgO含量呈明显的正相关关系,说明幔源岩浆发生过明显的结晶分异作用。地球化学分析表明,研究区基性岩墙属于板内拉斑玄武岩系列,与熊耳群火山岩有相似的地球化学特征;基于两者紧密的产出关系,我们认为该区岩墙可能是熊耳群火山岩的通道岩墙,共同代表了华北克拉通东、西陆块碰撞后伸展事件。  相似文献   

Evolution of the mass function of dark matter haloes     

Darren Reed  Jeffrey Gardner  Thomas Quinn  Joachim Stadel  Mark Fardal  George Lake  Fabio Governato 《Monthly notices of the Royal Astronomical Society》2003,346(2):565-572

We use a high-resolution ΛCDM numerical simulation to calculate the mass function of dark matter haloes down to the scale of dwarf galaxies, back to a redshift of 15, in a  50 h ⁻¹ Mpc  volume containing 80 million particles. Our low-redshift results allow us to probe low-σ density fluctuations significantly beyond the range of previous cosmological simulations. The Sheth & Tormen mass function provides an excellent match to all of our data except for redshifts of 10 and higher, where it overpredicts halo numbers increasingly with redshift, reaching roughly 50 per cent for the  10¹⁰–10¹¹ M_⊙  haloes sampled at redshift 15. Our results confirm previous findings that the simulated halo mass function can be described solely by the variance of the mass distribution, and thus has no explicit redshift dependence. We provide an empirical fit to our data that corrects for the overprediction of extremely rare objects by the Sheth & Tormen mass function. This overprediction has implications for studies that use the number densities of similarly rare objects as cosmological probes. For example, the number density of high-redshift  ( z ≃ 6) QSOs  , which are thought to be hosted by haloes at 5σ peaks in the fluctuation field, are likely to be overpredicted by at least a factor of 50 per cent. We test the sensitivity of our results to force accuracy, starting redshift and halo-finding algorithm.  相似文献   

METHODS   总被引：2，自引：0，他引：2  

Fig. Biandantang Lake  sampling sites are indicated by black circles 《中国海洋湖沼学报》2000,18(1):221-226

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A type curve approach to estimatingp for ap-normal transformation     

Dachang Li  Larry W. Lake 《Mathematical Geology》1995,27(3):359-371

The p-normal transformation plays an important role in reservoir characterization for data sets that are neither normally nor log-normally distributed. The key step in the transformation is to estimate the value of pfor a given data set. Even though there are several ways to determine p,these are more inconvenient than the quicker and easier type curve approach to estimate pwe present in this paper. In addition, the method provides the p-normal transformation with a visual interpretation. We demonstrate the technique by analyzing reservoir permeability and porosity data from the East Velma West Block Sims Sand Unit, Oklahoma.  相似文献   

Nitrogen isotope ratios in estuarine biota collected along a nutrient gradient in Narragansett Bay, Rhode Island, USA     

Pruell RJ  Taplin BK  Lake JL  Jayaraman S 《Marine pollution bulletin》2006,52(6):612-620

Stable nitrogen isotope ratios were used to study the incorporation of anthropogenically-derived nitrogen into the food webs of salt marsh systems along a contamination gradient in Narragansett Bay. Nitrogen isotope ratios (delta(15)N) were measured in six estuarine species collected from three marshes along this gradient, monthly from June to October between 1997 and 1999. A significant decrease in delta(15)N was found with distance along the estuary for four of the six species. Significant differences were found among monthly isotope ratios for some species. Nitrogen isotope ratios in sea lettuce (Ulva lactuca) increased during the summer season with highest delta(15)N values measured during September and October. This trend was most pronounced at the station receiving the highest nutrient inputs. Elevated delta(15)N values at this station appeared to correlate with seawater ammonia/nitrate concentration ratios. The temporal variations in delta(15)N suggest that care should be taken in species selection and the design of sampling schemes of studies using delta(15)N for monitoring anthropogenic nutrients in aquatic systems. Sampling programs designed to determine long-term trends should consider species that do not show rapid fluctuations in isotope ratios. The mud snail, Nassarius obsoletus, responded this way in the present study. Studies designed to measure short-term changes should include species such as U. lactuca, which rapidly respond to isotope changes. The results from this study also help to establish a baseline for nitrogen isotope values in Narragansett Bay. This information can be used to monitor future trends in nitrogen inputs to this estuary.  相似文献   

The influence of hurricane risk on tourist destination choice in the Caribbean     

Johanna Forster  Peter W. Schuhmann  Iain R. Lake  Andrew R. Watkinson  Jennifer A. Gill 《Climatic change》2012,114(3-4):745-768

Climate change could have major implications for the global tourism industry if changing environmental conditions alter the attractiveness of holiday destinations. Countries with economies dependent on tourism and with tourism industries reliant on vulnerable natural resources are likely to be particularly at risk. We investigate the implications that climate-induced variations in Atlantic hurricane activity may have for the tourism-dependent Caribbean island of Anguilla. Three hundred tourists completed standardised questionnaires and participated in a choice experiment to determine the influence hurricane risk has on their risk perceptions and decisions regarding holiday preferences. The hurricane season had been considered by 40?% of respondents when making their holiday choice, and the beaches, climate and tranquility of the island were more important than coral reef-based recreational activities in determining holiday destination choice. Choice models demonstrated that respondents were significantly less likely to choose holiday options where hurricane risk is perceived to increase, and significantly more likely to choose options that offered financial compensation for increased risk. However, these choices and decisions varied among demographic groups, with older visitors, Americans, and people who prioritize beach-based activities tending to be most concerned about hurricanes. These groups comprise a significant component of the island’s current clientele, suggesting that perceived increases in hurricane risk may have important implications for the tourism economy of Anguilla and similar destinations. Improved protection of key environmental features (e.g. beaches) may be necessary to enhance resilience to potential future climate impacts.  相似文献