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821.
822.
Keith A. Kvenvolden 《Geo-Marine Letters》1988,8(3):179-187
Methane, ethane, ethene, propane, and propene are common hydrocarbon gases in near-surface sediment from offshore areas in
the southern Pacific Ocean near Papua New Guinea, the Solomon Islands, Vanuatu, Tonga, New Zealand, and Antarctica. Sea floor
sites for sampling of sediment were selected on the basis of anomalies in marine seismic records, and the samples were intentionally
biased toward finding possible thermogenic hydrocarbon gases. In none of the areas, however, were thermogenic hydrocarbons
clearly identified. The hydrocarbon gases that were found appear to be mainly the products ofin situ microbial processes. 相似文献
823.
Keith M. Miller 《Marine Geodesy》2005,28(3):219-229
Concern over the impact of change in sea level is of topical interest internationally, but for the small island states of the Caribbean, a significant increase would prove to be catastrophic. The potential problem is being addressed as part of the much larger issue of climate change, and just this year a regional Climate Change Centre was established in Belize. Means of adapting to accommodate change will be considered under the Mainstream Adaptation to Climate Change (MACC) project, but initially the threat needs to be quantified. While meteorological offices have been accumulating weather data in some parts of the region for many years, sea level data is more scarce. This work puts least squares methods to test by applying them to spectral analysis of intermittent data sets acquired over periods of 6 and 9 years at two locations in Trinidad. The resulting sea level models that include 13 periodic components, datum bias, trend and atmospheric pressure are validated using fundamental historical information and observations that form the subject of discussion among local professional surveyors. Results show that while sea level at a location in North Trinidad is rising at the rate of about 1 mm a year, the change at a Southern site is about four times this amount. Horizontal movement has been measured across a tectonic fault that parts the island, and it is now apparent that there may be some vertical motion on this or some other fault lines in the region. 相似文献
824.
Although climate change is an urgent problem, behavioural and policy responses have not yet been sufficient to either reduce the volume of greenhouse gas emissions or adapt to a disrupted climate system. Significant efforts have been made to raise public awareness of the dangers posed by climate change. One reason why these efforts might not be sufficient is rooted in people’s need to feel efficacy to solve complex problems; the belief that climate change is unstoppable might thwart action even among the concerned. This paper tests for the effect of fatalistic beliefs on behavioural change and willingness to pay to address climate change using two cross-national surveys representing over 50,000 people in 48 nations.
Key policy insights
The perception that climate change poses a risk or danger increases the likelihood of behavioural change and willingness to pay to address climate change.
The belief that climate change is unstoppable reduces the behavioural and policy response to climate change and moderates risk perception.
Communicators and policy leaders should carefully frame climate change as a difficult, yet solvable, problem to circumvent fatalistic beliefs.
825.
We compute the big bang nucleosynthesis limit on the number of light neutrino degrees of freedom in a model-independent likelihood analysis based on the abundances of 4He and 7Li. We use the two-dimensional likelihood functions to simultaneously constrain the baryon-to-photon ratio and the number of light neutrinos for a range of 4He abundances Yp = 0.225–0.250, as well as a range in primordial 7Li abundances from (1.6 to 4.1) ×10−10. For (7Li/H)p = 1.6 × 10−10, as can be inferred from the 7Li data from Population II halo stars, the upper limit to Nν based on the current best estimate of the primordial 4He abundance of Yp = 0.238 is Nν < 4.3 and varies from Nν < 3.3 (at 95% C.L.) when Yp = 0.225 to Nν < 5.3 when Yp = 0.250. If 7Li is depleted in these stars the upper limit to Nν is relaxed. Taking (7Li/H)p = 4.1 × 10−10, the limit varies from Nν < 3.9 when Yp = 0.225 to Nν 6 when Yp = 0.250. We also consider the consequences on the upper limit to Nν if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed. 相似文献
826.
The radar ray path equations are used to determine the physical location of each radar measurement. These equations are necessary for mapping radar data to computational grids for diagnosis, display and numerical weather prediction (NWP). They are also used to determine the forward operators for assimilation of radar data into forecast models. In this paper, a stepwise ray tracing method is developed. The influence of the atmospheric refractive index on the ray path equations at different locations related to an intense cold front is examined against the ray path derived from the new tracing method. It is shown that the radar ray path is not very sensitive to sharp vertical gradients of refractive index caused by the strong temperature inversion and large moisture gradient in this case. In the paper, the errors caused by using the simplified straight ray path equations are also examined. It is found that there will be significant errors in the physical location of radar measurements if the earth’s curvature is not considered, especially at lower elevation angles. A reduced form of the equation for beam height calculation is derived using Taylor series expansion. It is computationally more efficient and also avoids the need to use double precision variables to mitigate the small difference between two large terms in the original form. The accuracy of this reduced form is found to be sufficient for modeling use. 相似文献
827.
为加强海上天然地震观测和岩石圈结构研究,我们在南海西沙群岛建立了石岛流动地震台,进行了为期一年多的观测试验.观测结果表明,虽然岛礁区的地震数据受热带气旋影响期间背景噪声较大,但仍能记录到MW 6级以上的地震.本文对具有清晰P波波形的远震记录进行了接收函数处理和计算模拟,得到台站下简单的地壳结构模型,其莫霍面深度为28 km,上地壳顶部有一层2 km厚的低速层,横波速度只有23 km/s,向下逐渐过渡到横波速度为38 km/s的下地壳.与已有的研究结果比较,发现石岛台与琼中台的地壳结构模型是西沙海槽剖面的自然延伸,西沙地块的地壳结构属减薄型陆壳,可与华南地块的正常陆壳对比. 相似文献
828.
We present results from an experiment that wasdesigned to investigate turbulent transportrelationships in a nearly homogeneous boundary layerdisturbed by unsteady wind swings, as found at thebase of an advective inversion with a convectiveboundary layer overhead. In such a situation wemeasured vertical gradients and eddy fluxes of temperature andhumidity at two heights. From these, the turbulentdiffusivities of heat and water vapour are obtained,and compared to the predictions of Monin–Obukhovsimilarity theory and those of a numericalsecond-order closure model. It is found that themeasured diffusivities exceed both predictions. Thisis interpreted as a consequence of the unsteadyconditions. It is also found that the diffusivity forheat is roughly 10% larger than that for watervapour. This is in agreement with a theoreticaltreatment of the unsteadiness effects that wedeveloped in an earlier publication. This result isnot reproduced by the numerical model because themodel has no provision for unsteady conditions. Ourresult disagrees with that from an earlier, verysimilar, field experiment, which may be due to asystematic underestimation of sensible heat flux inthe older experiment. 相似文献
829.
The mechanisms responsible for the seasonal cycle in the tropical central and eastern Pacific sea surface temperature (SST)
are investigated using a coupled general circulation model. We find that the annual westward propagation of SST anomalies
along the equator is explained by a two-stage process. The first stage sets the phase of the variation at the eastern boundary.
The strengthening of the local Hadley Circulation in boreal summer leads to a strengthening of the northward winds that blow
across the equator. These stronger winds drive enhanced evaporation and entrainment cooling of the oceanic mixed layer. The
resulting change in SST is greatest in the east because the mixed layer is at its shallowest there. As the east Pacific SST
cools the zonal SST gradient in the central Pacific becomes more negative. This development signals the onset of the second
stage in the seasonal variation of equatorial SST. In response to the anomalous SST gradient the local westward wind stress
increases. This increase drives cooling of the oceanic mixed layer in which no single mechanism dominates: enhanced evaporation,
wind-driven entrainment, and westward advection all contribute. We discuss the role that equatorial upwelling plays in modulating
mixed layer depth and hence the entrainment cooling, and we highlight the importance of seasonal variations in mixed layer
depth. In sum these processes act to propagate the SST anomaly westward.
Received: 22 February 1999 / Accepted: 20 March 2000 相似文献