Climatic variations in the coastal zone — Comparison between the Po River delta (Adriatic Sea,Italy) and the Huanghe River delta (Bohai Sea,China)     

Francesco Marabini  Antonio Veggiani  Qin Yunshan  Cang Shuxi 《中国海洋湖沼学报》1993,11(3):193-206

The aim of this work is to research the influence of natural climatic changes on the evolution of the coastal zone in modern times and the possible implication of human activities on the configuration of the present coastline. Comparison of data of two very far and different areas, the Po River delta, Adriatic Sea and the Huanghe River delta, Bohai Sea, reveals the planetary diffusion of climatic fluctuations and their effects on coastal evolution. Contribution No. 820 from the Marine Geology Institute, C. N. R., Italy. Contribution No.2207 from the Institute of Oceanology, Academia Sinica. Project supported by the National Natural Science Foundation of China.  相似文献   

Short-term intrinsic-intensity variations of pulsars     

S. Krishnamohan  V. Balasubramanian 《Journal of Astrophysics and Astronomy》1984,5(4):483-493

Pulsars show intensity variations over timescales ranging from a few microseconds to a few years. Short-term intensity variations,i.e. those having timescales of a few minutes to a few hours had been difficult to study as their timescales are similar to those due to interstellar scintillations. We present here a method to separate the autocorrelation function of the short-term broadband intensity variations from that of the interstellar scintillations and thus overcome the above difficulty. The method assumes that the intrinsic variations are correlated over a bandwidth much larger than the decorrelation bandwidth for scintillations. Hence the ratio of the power in the variations due to the two causes depends on the bandwidth used. By applying the method to the intensity variations of 24 pulsars, we show that the presence of short-term intrinsic variations is very common in the radiation of pulsars. Quasi-periodicities were detected in the intensity variations of many pulsars, but their origin is not clear.  相似文献   

由南北朝以前171个月掩星记录所得到的地球自转长期变化   总被引：1，自引：0，他引：1  

刘次沅 《中国天文和天体物理学报》1988,(2)

应用“实际可见时间段”方法研究中国古代只有日期而无观测时刻的月掩星记录,文中讨论了这些记录的真实性及其含义,由南北朝以前的58个月掩行星和113个月掩恒星记录分别得到公元1,4,5,6世纪的地球自转参数△t和ω平均值为ω=-66.8秒/世纪~2。  相似文献   

Spatial and seasonal variations in the chemistry of sediment interstitial waters in the Tamar Estuary     

P.G. Watson  P.E. Frickers  C.M. Goodchild 《Estuarine, Coastal and Shelf Science》1985,21(1):105-119

Chemical concentration gradients in the interstitial waters of shallow (0–10 cm), reducing sediments are reported for four stations in the Tamar Estuary over a two-year period. The products of organic matter breakdown, sedimentary redox changes and diagenetic reactions have been determined and a multicomponent analytical approach has enabled the interactions of complementary processes to be examined. While many components show spatial and seasonal patterns related to the supply of organic matter and salinity associated sulphate distribution, the effects of temperature, sediment disturbance and river flow are also apparent.Sediment stored prior to the separation of interstitial water showed significant changes in chemical composition compared to samples processed within 24 h of collection.  相似文献   

Structural aspects of the surf-zone fish assemblage at King's Beach,Algoa Bay,South Africa: Long-term fluctuations     

Theresa A. Lasiak 《Estuarine, Coastal and Shelf Science》1984,18(4):459-483

Regular collections of fish were obtained from the surf-zone at King's Beach, Algoa Bay. A total of 3970 fish, representing 50 species was caught with a coarse net and 16 857 fish, representing 37 species, were caught with a fine net. Predominant species were the blacktail, Diplodus sargus; the sand steenbras, Lithognathus mormyrus; the mullet, Liza richardsoni; the gorrie, Pomadasys olivaceum; the white stumpnose, Rhabdosargus globiceps; the sandshark, Rhinobatos annulatus; and the streepie, Sarpa salpa. No seasonal trends were discernible in the overall abundance or species diversity. The species composition of the dominant component of the fish assemblage varied considerably. This indicated instability in the community structure and cast doubts on the applicability of a classic community concept and the use of diversity indices. Neither classification nor correspondence analysis were of any use in identifying a characteristic species component. Multiple regression analysis indicated that short-term variations in wind conditions might be a primary determinant of fluctuations in abundance. The lack of seasonality in the community parameters may reflect the fact that short-term variability masks seasonal perturbations.  相似文献   

非洲地区大气气溶胶光学厚度时空变化及亚速尔高压对沙尘越大西洋传输的影响          下载免费PDF全文

高玮  屈文军 《山东气象》2018,38(4):81-92

研究了非洲地区大气气溶胶光学厚度（AOD）的时空变化及沙尘气溶胶越大西洋海区的传输。结果表明：1）源于撒哈拉沙漠的沙尘及其随赤道东风向西输送使得沙尘气溶胶成为非洲沙漠地区和紧邻的大西洋海区的主要气溶胶组分;AOD高值区和沙尘气溶胶光学厚度高值区在1—7月随赤道辐合带北移同步向北移动,而在8—12月则向南回撤。2）刚果盆地大气气溶胶主要为热带雨林和稀树草原排放的有机碳（OC）和黑碳（BC）气溶胶;其中与生物质燃烧源排放有关的OC、BC高值主要集中在干季（6—9月）的后半段（8—9月）;而生物源OC排放全年连续,其排放峰值出现于雨季开始时;生物质燃烧排放高值期与生物源排放高值期前后相继,形成干季（尤其是后半段）时期的OC、BC光学厚度高值。3）亚马逊河入海口地区主要气溶胶组分为海盐气溶胶,9—11月该区风力输送增强,风向由东南风转变为东风,海盐进入亚马逊河入海口处,形成AOD和海盐气溶胶光学厚度高值区。4）撒哈拉沙漠沙尘气溶胶向大西洋传输的偏北月份为7—9月、偏南月份为1—3月;2000—2016年海区沙尘气溶胶的传输路径存在向南移动的变化趋势,与同期亚速尔高压的增强和沙尘传输路径以北北风分量的增强以及赤道辐合带的移动一致。上述研究结果揭示了利用大气气溶胶时空变化特征反映区域大气环流和气候变化的可能性。  相似文献   

VARIABILITY IN THE WESTERN PACIFIC SUBTROPICAL HIGH AND ITS RELATIONSHIP WITH SEA TEMPERATURE VARIATION CONSIDERING THE BACKGROUND OF CLIMATE WARMING OVER THE PAST 60 YEARS     

孙圣杰  李栋梁 《热带气象学报(英文版)》2018,24(4):468-480

By adopting characteristic index data for the Western Pacific Subtropical High (WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and the National Oceanic and Atmospheric Administration (NOAA) sea surface temperature (SST) data, we studied the WPSH variability considering the background of climate warming by using a Gaussian filter, moving averages, correlation analysis, and synthetic analysis. Our results show that with climate warming over the past 60 years, significant changes in the WPSH include its enlarged area, strengthened intensity, westward extended ridge point and southward expanded southern boundary, as well as enhanced interannual fluctuations in all these indices. The western ridge point of the WPSH consistently varies with temperature changes in the Northern Hemisphere, but the location of the ridgeline varies independently. The intensity and area of the WPSH were both significantly increased in the late 1980s. Specifically, the western ridge point started to significantly extend westward in the early 1990s, and the associated interannual variability had a significant increase in the late 1990s; in addition, the ridgeline was swaying along the north-south-north direction, and the corresponding variability was also greatly enhanced in the late 1990s. With climate warming, the SST increase becomes more weakly correlated with the WPSH intensity enhancement but more strongly correlated with the westward extension of the ridge point in the equatorial central and eastern Pacific Ocean in winter, corresponding to an expanding WPSH in space. In the northern Pacific in winter, the SST decrease has a weaker correlation with the southerly location of the ridgeline but also a stronger correlation with the westward extension of the ridge point. In the tropical western Pacific in winter, the correlations of the SST decrease with the WPSH intensity enhancement, and the westward extension of the ridge point is strengthened. These observations can be explained by strengthened Hadley circulations, the dominant effects of the southward shift, and additional effects of the weakened ascending branch of the Walker circulation during warm climatological periods, which consequently lead to strengthened intensities, increased areas, and southward expansions of the WPSH in summer.  相似文献   

Response of the North Pacific Storm Track Activity in the Cold Season to Multi-scale Oceanic Variations of Kuroshio Extension System: A Statistical Assessment     

Peilong YU  Minghao YANG  Chao ZHANG  Yi LI  Lifeng ZHANG  Shiyao CHEN 《大气科学进展》2023,40(3):514-530

In this paper, a statistical method called Generalized Equilibrium Feedback Analysis(GEFA) is used to investigate the responses of the North Pacific Storm Track(NPST) in the cold season to the multi-scale oceanic variations of the Kuroshio Extension(KE) system, including its large-scale variation, oceanic front meridional shift, and mesoscale eddy activity.Results show that in the cold season from the lower to the upper troposphere, the KE large-scale variation significantly weakens the storm tr...  相似文献   

Application of the Dynamic Cone Penetrometer (DCP) for determination of the engineering parameters of sandy soils     

S.D. Mohammadi  M.R. Nikoudel  H. Rahimi  M. Khamehchiyan 《Engineering Geology》2008,101(3-4):195-203

Determination of the in situ engineering properties of foundation materials has always been a challenge for geotechnical engineers and, thus, several methods have been developed so far. Dynamic Cone Penetration (DCP) test is one of the most versatile amongst them. In the present research, a light weight simple DCP device was developed and used for evaluation of the engineering properties of sandy soils in laboratory conditions. The device consisted of an 8-kg hammer that drops over a height of 575 mm, and drives a 60° cone tip with 20 mm base diameter into the ground. To control the validation of the results, laboratory direct shear and plate load tests were used as reference tests. The soil sample was a poorly graded sandy soil (SP) taken from alluvial deposits of the Tehran plain. All DCP tests and PLTs were undertaken on compacted soil in a mould with 700 mm diameter and 700 mm height. Based on the results of the experiments, the relationships between Dynamic Penetration Index (DPI), relative density (D_r), modulus of elasticity (E), shear modulus (G), modulus of subgrade reaction (K_S), and the friction angle of the soil were obtained with a high coefficient of determination (> 90%). The repeatability of the test results was also evaluated by calculating the coefficient of variations (C_v), which was less than 30% for all tests.  相似文献   

Losses from sleet storms in the United States     

Stanley A. Changnon 《Natural Hazards》2008,47(3):465-470

Increasing losses of life and property and damages to the environment due to sleet and related winter storm conditions have increased the need for long-term sleet storm data to better assess the point and regional risks of sleet and their long-term variations. The areas of greatest losses and frequency of catastrophes caused by sleet during 1971–2007 are the Northeast and Central regions of the U.S. These two regions experienced 72% of all the nation’s sleet losses. Most of the western U.S. had no damaging sleet-related events or losses. When sleet losses occurred, they tended to be in 2, 3, or 4 adjacent states. Sleet catastrophes were most common in January with 15 of the 30 events. The earliest storm occurred in October and the latest in March. The temporal distributions of catastrophes and their losses during 1971–2007 were similar. Both showed a secondary peak in 1976–1979, a low in 1988–1991, and then high values during the 1996–2007 period. The temporal distributions of damaging storms and losses indicate an upward trend over time.  相似文献