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1.
There is a growing practical interest in the ability to increase the sea states at which marine operations can be safely undertaken by exploiting the quiescent periods that are well known to exist under a wide range of sea conditions. While the actual prediction of quiescent periods at sea for the control of operations is a deterministic process, the long term planning of future maritime tasks that rely on these quiescent periods is a statistical process involving the anticipated quiescence properties of the forecasted sea conditions in the geographical region of interest. It is in principle possible to obtain such data in tabular form either large scale simulation or from field data. However, such simulations are computationally intensive and libraries of appropriate field data are not common. Thus, it is clearly attractive to develop techniques that exploit standard wave spectral models for describing the quiescence statistics directly from such spectra. The present study focuses upon such techniques and is a first step towards the production of a computationally low-cost quiescence prediction tool and compares its efficacy against simulations. Two significant properties emerge for a large class of wave spectral models that encompasses the ubiquitous Neumann and Pierson Moskowitz or Bretschneider forms. Firstly, the auto-correlation function of the wave profile that are required to produce the quiescence property can be obtained analytically in terms of standard special functions. This considerably reduces the computational cost making desktop computer-based planning tools a reality. Secondly, for each class of these parametric spectra, the probability of a given number of consecutive wave heights (normalised to the significant wave heights) less than some critical value is in fact independent of absolute wave height. Thus, for a broad class of practically interesting wave spectra all that is required to obtain the statistical distribution of the quiescent periods is simple rescaling. 相似文献
2.
We evaluate the exposure during nadir observations with JEM-EUSO, the Extreme Universe Space Observatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mission to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth’s nighttime atmosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by ultra-high energy cosmic rays. In the present work, we discuss the particularities of space-based observation and we compute the annual exposure in nadir observation. The results are based on studies of the expected trigger aperture and observational duty cycle, as well as, on the investigations of the effects of clouds and different types of background light. We show that the annual exposure is about one order of magnitude higher than those of the presently operating ground-based observatories. 相似文献
3.
借鉴梅雨指数的定义,选取贵溪、德兴、玉山、衢州、龙泉为5个代表站,建立了江南南部初夏雨季指数。近50a来,江南南部初夏雨季平均开始日和结束日分别是6月10日和7月1日,比江淮梅雨早约8d左右;雨季平均长度为20．5d,雨季内雨日数平均为15．5d;江南南部初夏雨季开始日经历了一个显著的“V型”变化过程,结束日呈“纺锤型”振荡变化;雨季的长度和雨日数没有明显的线性趋势变化,但20世纪80年代期间的雨季长度和雨日数年际变化大,旱涝频率高、强度强;20世纪60年代和21世纪以后雨季偏弱年较多。影响江南南部初夏雨季开始早晚的大气环流关键区主要在乌拉尔山附近,若乌拉尔山附近为阻高型（低槽型）,则雨季开始早（晚）;中高纬系统、太平洋副高和南亚高压也都有影响。影响雨季强度的大气环流关键区分别在东半球的北极区、中低纬度西北太平洋和鄂霍次克海附近上空。 相似文献
4.
Carbon isotope ratio (δ13C) values of lipid biomarkers from plants can be used to assess water use efficiency and to reconstruct environmental conditions in the past. We assessed the effect of salinity on the δ13C values for leaf wax n-C31 and n-C33 alkanes, bulk leaf matter and leaf total lipid extracts from Avicennia marina (gray mangrove) trees growing along the Brisbane River estuary in Queensland, Australia. We observed an increase in 0.19 ± 0.053‰ (R2 0.61, p 0.008) and 0.16 ± 0.052‰ (R2 0.55, p 0.01) per salinity unit for the two n-alkanes, respectively, and of 0.087 ± 0.028‰ (R2 0.41, p 0.009) for whole leaves per salinity unit, indicating that water use efficiency of A. marina increased with the salt content of water. There was no correlation between δ13C values of total lipid extracts and salinity, perhaps because of a decrease in lipid concentration at higher salinity or because of varying contributions of different lipid classes to the extract. The robust relationship between salinity and δ13C values of leaf wax lipids provides a means of quantitatively reconstructing past salinity from carbon isotope ratios of mangrove lipid biomarkers in sediments. When paired with measurements of the hydrogen isotope ratio values of the same compounds, the approach should facilitate quantitative reconstruction of the hydrogen isotope composition of environmental water. In order for the method to successfully reconstruct past salinity and water isotopes, a mangrove source for leaf wax would need to be confirmed by palynological or other evidence, or the isotopic composition of a more source specific biomarker, such as taraxerol, would need to be measured. 相似文献
5.
2015年11月浙江省降水异常成因分析 总被引：1，自引：1，他引：0
利用NCEP/NCAR大气环流资料、NOAA ERSST.V3b海温资料以及浙江省66个台站1971年以来的降水资料,分析了浙江省11月降水偏多对应的高低层大气环流异常特征以及与热带海温异常的联系,并在此基础上对2015年11月浙江省降水异常偏多的事实进行梳理和个例诊断。结果显示,2015年11月浙江省处于降水偏多的气候背景,同时北半球北极涛动正位相异常偏强、中高纬地区经向环流偏弱,西北太平洋副热带高压强度异常偏强、位置偏西是造成降水异常偏多的主要原因;统计分析表明巴尔喀什湖地区500 hPa高度场和西太平洋副热带高压强度与浙江省11月份降水具有显著相关;厄尔尼诺是导致浙江省11月降水偏多的重要外强迫因子之一,2015年11月Niño3.4指数达历史峰值,是造成浙江省同期降水异常偏多的主要原因。 相似文献
6.
《Ocean & Coastal Management》2000,43(4-5):427-444
Successful coastal management requires appropriate competencies. Higher education is under pressure to motivate and produce graduates with the relevant scientific background. In order to make these graduates more employable, employers’ participation to education is required. Because of the interdisciplinary nature of the subject area and the need for well-skilled professionals, networking is vital for building links between industry, managers, policy-makers and academia. New curricula need to be developed and adapted to a constantly evolving subject and learning environment. The virtual classroom is now a reality. The use of electronic communication should allow the involvement of all stakeholders, including Non-Governmental Organisations (NGOs). NGOs will take a more and more important rôle in the dissemination of scientific information and its application to coastal management. Generalisations are based on a case study: University College Scarborough, England. 相似文献
7.
江南南部初夏雨季的降水和环流气候特征 总被引：3，自引：0，他引：3
基于1961～2010年气象台站逐日降水资料、同期美国NCEP/NCAR的逐日再分析格点资料,通过气候平均、REOF分析、聚类分析等方法,分析了江南地区初夏降水的地域性和时段性特征,及西太平洋副高和高、低空急流等大气环流的相应演变过程。结果发现:（1）江南南部27.5°～29.5°N存在一个独立于华南前汛期和江淮梅雨的初夏雨季,该雨季平均发生时间为6月11～30日,比江淮梅雨早约8天左右。（2）西太平洋副高的西伸东退是江南南部初夏雨季发生发展的重要环流背景,6月第2候副高发生突变性加速西伸之后雨季开始,雨季期间850 hPa副高西伸脊点基本稳定在最西位置即133°E附近,6月第6候副高东退北抬后雨季结束。（3）低层急流大风带的形成和位置是江南南部初夏雨季阶段的重要动力条件,印度洋和孟加拉湾向东北延伸的低层急流与西太平洋副高西北侧的气流连通形成低层急流大风带,并与北侧上空的高空急流耦合,降水集中区位于低层急流大风带左侧、高空急流入口区右侧。 相似文献
8.
M. Rodrigo-Gámiz F. Martínez-Ruiz F.J. Jiménez-Espejo D. Gallego-Torres V. Nieto-Moreno O. Romero D. Ariztegui 《Quaternary Science Reviews》2011,30(15-16):2018-2034
Eolian input fluctuations and paleoceanographic conditions in the western Mediterranean have been reconstructed by using a multi-proxy approach to infer climate variability for the last 20,000 yr. A sediment core from the East Alboran Sea basin provides high-resolution geochemical, mineralogical and grain size distribution records from the Last Glacial Maximum onward. The accurate chronology obtained, closely related with the North Greenland Ice core Project, has provided a detailed paleoclimate reconstruction at the centennial–millennial time scale. Mineral and chemical compositions as well as sediment grain size distribution have been used to establish both fluvial and eolian input variations, deep-water current intensity, and ventilation and productivity conditions at the time of deposition. During the cold period Greenland Stadial-2a, the analyzed proxies evidence significant climate oscillations. Redox proxies, showing marked Mn/Al and Fe/Al peaks, as well as granulometric parameters, support major changes in thermohaline circulation, with active circulation triggered by the Western Mediterranean Deep Water formation. Ba/Al ratios and the presence of authigenic barite point to high productivity during the Last Heinrich event. At this time, Zr/Al, Si/Al and Ti/Al ratios as well as quartz and palygorskite contents also corroborate dryer conditions in the Alboran borderlands, with a major reorganization of atmospheric circulation at the beginning of the deglaciation and during the Last Heinrich event. In contrast, a decreasing trend in the Zr/Al ratio and increasing Mg/Al, K/Al and illite + chlorite/kaolinite ratios would indicate enhanced river runoff and supporting lower eolian dust input and wetter periods during the Bölling–Alleröd. Short-term and abrupt climate oscillations such as the Intra-Alleröd Cold Period are likewise reflected by minor yet conspicuous changes in eolian proxies. During the Younger Dryas, we distinguish an initial cold and dry phase, with major westerlies intensity, thermohaline reactivation, and high productivity levels, and a second wetter phase characterized by sporadic rainfalls over poorly vegetated surrounding continental areas. Then, during the Holocene, alternating phases of major humidity and aridity were recorded by major fluctuations in detrital input. These are also correlated with recurrent forest cover declines reported from pollen records, with a noteworthy early decline in the African Humid Period. During the Holocene, an initial demise of the Last Organic-Rich Layer is also evidenced, tentatively associated with aspiration forces promoted by intense thermohaline circulation through the Gibraltar Strait. 相似文献
9.
A minimal three-dimensional hurricane model formulated on an \(f\) -plane is used to investigate the asymmetries that develop when a model storm is subjected to ambient vertical wind shear. The asymmetries that form in the moist version of the model have a different structure to those that form in a dry version. In the moist case, there are two competing factors that influence the inner-core asymmetries: vertical wind shear and frictional convergence in the boundary layer. We show that the relative importance of these factors is different in the different stages of vortex evolution and different also in the core region compared with the outer region of the vortex. In the developing stage, the patterns of vertical velocity and temperature deviation above the boundary layer are primarily determined by the shear. When saturation occurs in the core region, the vortex rapidly intensifies and the upper and lower portions of the vortex become strongly coupled so that there is little tilt of the core region. In the mature stage, ascent associated with frictional convergence in the core tends to dominate the vertical motion field induced by the shear, but there are individual times when the patterns of ascent at the top of the boundary layer and at the upper level differ significantly. These times coincide mostly with fluctuations in the vortex track, which, in turn, must be influenced by asymmetries in the horizontal flow in the vortex. Even though the inner core of the vortex becomes upright with the onset of deep moist convection, the outer regions continue to have a significant tilt. Outside the core region, the asymmetries in the pattern of vertical motion above the boundary layer are associated primarily with the tilt of the outer vortex. 相似文献
10.
利用NCEP/NCAR全球再分析资料、地面观测资料和自动站降水资料,分析了2018/2019年冬季浙江罕见连续阴雨寡照天气过程中冬季风环流和南支槽等环流异常,并从西风带波动、海温强迫等方面研究了局地环流异常的成因。结果表明:2018/2019年冬季连阴雨事件中雨日、日照破历史记录,雨量较常年同期明显偏多。主要的环流异常为西北太平洋异常反气旋（WNPAC）明显偏北,同时阿留申低压和西伯利亚高压亦偏北,东亚地区40°N以南有强的偏南风异常,冬季风偏弱;南支槽较常年偏强,保证了浙江上空有持续的水汽和扰动输送。对流层中层存在沿欧洲向东亚—西太平洋传播的波动能量,波能在东亚地区一直向南传播至20°N以南,可能导致WNPAC明显北抬和南支槽加强。ENSO是WNPAC的重要强迫源,ENSO暖位相使得海洋性大陆出现异常对流冷却,而浙江上空对流加强,ENSO对南支槽活动强度亦有明显的制约作用。中国近海海温偏高是WNPAC和阿留申低压明显偏北的重要影响因素。2018/2019年冬季局地环流异常可能由ENSO和中国近海海温协同强迫所致。 相似文献