Response of a climate model to tidal mixing parameterization under present day and last glacial maximum conditions     

lvaro Montenegro  Michael Eby  Andrew J. Weaver  Steven R. Jayne 《Ocean Modelling》2007,19(3-4):125-137

Experiments with a climate model were conducted under present day and last glacial maximum conditions in order to examine the model’s response to a vertical mixing scheme based on internal tide energy dissipation. The increase in internal tide energy flux caused by a 120 m reduction in sea level had the expected effect on diffusivity values, which were higher under lower sea level conditions. The impact of this vertical diffusivity change on the Atlantic meridional overturning is not straightforward and no clear relationship between diffusivity and overturning is found. There exists a weak positive correlation between overturning and changes to the power consumed by vertical mixing. Most of the climatic response generated by sea level change was not related to alterations in the internal tide energy flux but rather to the direct change in sea level itself.  相似文献   

深厚覆盖层上高土石坝极限抗震能力分析   总被引：6，自引：1，他引：5  

赵剑明  温彦锋  刘小生  陈宁  常亚屏  刘启旺  王宏 《岩土力学》2010,31(Z1):41-47

针对强震区深厚覆盖层上高土石坝的特点,在三维真非线性有效应力地震反应分析基础上,提出了一套深厚覆盖层上高土石坝极限抗震能力的研究方法。从稳定、变形、防渗体安全等方面,对建在深厚覆盖层上的长河坝高心墙堆石坝的极限抗震能力进行了研究和分析。根据坝坡稳定性、地震残余变形、液化可能性、单元抗震安全性、防渗心墙及坝基防渗墙安全等多角度的评价结果,初步认为,长河坝的极限抗震能力为0.50～0.55g。  相似文献   

Late Quaternary glaciation and equilibrium-line altitudes of the Mayan Ice Cap, Guatemala, Central America     

Alex J. Roy  Matthew S. Lachniet 《Quaternary Research》2010,74(1):1-7

The Sierra los Cuchumatanes (3837 m), Guatemala, supported a plateau ice cap and valley glaciers around Montaña San Juan (3784 m) that totaled ∼ 43 km² in area during the last local glacial maximum. Former ice limits are defined by sharp-crested lateral and terminal moraines that extend to elevations of ∼ 3450 m along the ice cap margin, and to ca. 3000-3300 m for the valley glaciers. Equilibrium-line altitudes (ELAs) estimated using the area-altitude balance ratio method for the maximum late Quaternary glaciation reached as low as 3470 m for the valley glaciers and 3670 m for the Mayan Ice Cap. Relative to the modern altitude of the 0°C isotherm of ∼ 4840 m, we determined ELA depressions of 1110-1436 m. If interpreted in terms of a depression of the freezing level during maximal glaciation along the modern lapse rate of − 5.3°C km^− 1, this ΔELA indicates tropical highland cooling of ∼ 5.9 to 7.6 ± 1.2°C. Our data support greater glacial highland cooling than at sea level, implying a high tropical sensitivity to global climate changes. The large magnitude of ELA depression in Guatemala may have been partially forced by enhanced wetness associated with southward excursions of the boreal winter polar air mass.  相似文献   

非线性Hoek-Brown强度折减技术   总被引：1，自引：1，他引：0  

符文熹  王启鸿  刘长武 《地质灾害与环境保护》2010,21(2):82-87

为精确执行非线性Hoek-Brown(HB)强度折减,首先在p-q空间分析了HB曲线任意点切线与Mohr-Coulomb(MC)准则的对应关系,推求了HB屈服函数材料折减系数和强度折减系数的关系,提出了潜入强度折减系数的HB弹塑性分析模型,介绍了在Flac3D平台上二次开发实现非线性HB强度折减的基本思路。对一边坡算例用本文方法和简化Bishop法进行了对比分析,计算结果表明,潜入强度折减系数的HB弹塑性模型计算获得的边坡潜在滑动面形态、位置和相应的安全系数,与简化Bishop法计算结果很接近。  相似文献   

1981—2011年阿里河地区气温极差变化浅析     

李哲  杨恺  包晗  王超 《内蒙古气象》2014,(1):19-21

利用1981—2011年阿里河镇的平均气温及逐日最高、最低气温资料,详细分析了年平均气温、年极端最高气温、年极端最低气温以及年平均气温极差的变化规律和特点。结果表明:阿里河地区的年平均气温呈明显上升趋势;年极端最高、最低气温都呈上升趋势;年平均气温极差值逐渐增大。  相似文献   

Water discharge variability of Changjiang （Yangtze） and Huanghe （Yellow） Rivers and its response to climatic changes     

张喜林  范德江  王厚杰  杨作升 《中国海洋湖沼学报》2014,32(6):1392-1405

Influences of large-scale climatic phenomena, such as the E1Nifio/La Nifia-Southem Oscillation （ENSO） and the Pacific Decadal Oscillation （PDO）, on the temporal variations of the annual water discharge at the Lijin station in the Huanghe （Yellow） River and at the Datong station in the Changjiang （Yangtze） River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis （EMD- MESA） method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the inter- annual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.  相似文献   

Modeling seasonal variations of subsurface chlorophyll maximum in South China Sea   总被引：1，自引：0，他引：1  

Xiang Gong  Jie Shi  Huiwang Gao 《中国海洋大学学报(英文版)》2014,13(4):561-571

In the South China Sea(SCS), the subsurface chlorophyll maximum(SCM) is frequently observed while the mechanisms of SCM occurrence have not been well understood. In this study, a 1-D physical-biochemical coupled model was used to study the seasonal variations of vertical profiles of chlorophyll-a(Chl-a) in the SCS. Three parameters(i.e., SCM layer(SCML) depth, thickness, and intensity) were defined to characterize the vertical distribution of Chl-a in SCML and were obtained by fitting the vertical profile of Chl-a in the subsurface layer using a Gaussian function. The seasonal variations of SCMs are reproduced reasonably well compared to the observations. The annual averages of SCML depth, thickness, and intensity are 75 ± 10 m, 31 ± 6.7 m, and 0.37 ± 0.11 mg m-3, respectively. A thick, close to surface SCML together with a higher intensity occurs during the northeastern monsoon. Both the SCML thickness and intensity are sensitive to the changes of surface wind speed in winter and summer, but the surface wind speed exerts a minor influence on the SCML depth; for example, double strengthening of the southwestern monsoon in summer can lead to the thickening of SCML by 46%, the intensity decreasing by 30%, and the shoaling by 6%. This is because part of nutrients are pumped from the upper nutricline to the surface mixed layer by strong vertical mixing. Increasing initial nutrient concentrations by two times will increase the intensity of SCML by over 80% in winter and spring. The sensitivity analysis indicates that light attenuation is critical to the three parameters of SCM. Decreasing background light attenuation by 20% extends the euphotic zone, makes SCML deeper(~20%) and thicker(12% – 41%), and increases the intensity by over 16%. Overall, the depth of SCML is mainly controlled by light attenuation, and the SCML thickness and intensity are closely associated with wind and initial nitrate concentration in the SCS.  相似文献   

Warmer-Get-Wetter or Wet-Get-Wetter? A Criterion to Classify Oceanic Precipitation     

Chengcheng Qian  Ge Chen 《中国海洋大学学报(英文版)》2014,13(4):552-560

In this study, the temporal and spatial variations of observed global oceanic precipitation during 1979–2010 are investigated. It is found that the global trend in precipitation during this period varies at a rate of 1.5%/K of surface warming while the rate is 6.6%/K during 2006–2010. The precipitation is highly correlated with Sea Surface Temperature(SST) in both the temporal and the spatial patterns since the strong 1997–98 El Nino event. Considering the distributions of precipitation and SST, seven oceanic regions are classified and presented using the observed Global Precipitation Climatology Project(GPCP) data and Extended Reconstructed Sea Surface Temperatures, version 3(ERSST.v3) data. Further examining the mechanisms of the classified oceanic precipitation regions is conducted using the Tropical Rainfall Measuring Mission(TRMM) satellite, GFDL-ESM-2G model precipitation and SST data and Hadley Center sea ice and SST version 1(Had ISST1) data. More than 85% of global oceanic precipitations are controlled by either one or both of the warmer-get-wetter mechanism and wet-get-wetter mechanism. It is estimated that a 0.5 SST signal-to-noise ratio, representing the trend of SST time series to the standard deviation, is a criterion to distinguish the mechanism of a region. When the SST ratio is larger than 0.5, the precipitation of this region is controlled by the warmer-get-wetter mechanism. SST, rather than the humidity, is the pivotal factor. On the other hand, when the SST ratio is less than 0.5, the precipitation is controlled by the wet-get-wetter mechanism. The SST variability is a significant factor contributing to the precipitation variation.  相似文献   

Experimental research on the mechanical properties of methane hydrate-bearing sediments during hydrate dissociation     

《Marine and Petroleum Geology》2014

This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of −5 °C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus E_S of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E₀ was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr–Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M–C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region.  相似文献   

Last glacial emplacement of methane-derived authigenic carbonates in the Sea of Japan constrained by diatom assemblage,carbon-14, and carbonate content     

《Marine and Petroleum Geology》2014

We studied diatom assemblages and CaCO₃ contents of methane-derived authigenic carbonates from the eastern margin of the Sea of Japan and assessed the formation time of these samples. Radioactive ¹⁴C date was determined in selected samples to obtain the maximum age of the time. The results of our study suggest mass formation of carbonate nodules in a glacial period within ∼40 ky, consistent with a published U/Th dating result of carbonate nodules in the study area. Diatom assemblages and contents in the carbonate nodules (abundance of ∼10⁶/g, dominance of neritic-littoral species, warm/cold water species ratio lower than ∼25) differ from the near-seafloor sediments in the study area, which have characteristics of Holocene sediments in the Sea of Japan, and suggest cementation of glacial sediments. Laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi-enclosed ocean. Similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules. Glacial sediments with oceanic cold water species as low as Holocene sediments restricts the sediment age to before 20 cal. ky BP. Carbonate contents higher than 78 wt% suggest the cementation of poorly compacted sediments near the seafloor, and the date of carbonate cementation is, therefore, close to that of the cemented sediments. Most carbonate nodule samples in this study were formed in a glacial period and detection of ¹⁴C restricts this period to within ∼40 ky.  相似文献