天津沿海赤潮发生的基本特征研究     

张琪  孙家伟  冯延竹  李希彬  王鲁宁  崔健 《海洋预报》2020,37(1):62-66

使用《天津市海洋环境状况公报》中的数据,分析天津沿海赤潮发生的特征。通过分析发现2005-2017年天津海域共发生赤潮30次,累计发生面积4 695 km2。天津沿海赤潮发生主要集中在夏季,又以8月最多,占赤潮发生总数的30%。通过赤潮优势种的分析发现近年来天津海域赤潮生物的优势种类有不断增加的趋势。同时本文从水文气象条件诱发赤潮的角度分析得出了天津沿海最易发生赤潮的天气形势,天津沿海25~27℃水温范围内赤潮发生较多,最适宜赤潮发生的风速为3、4级风,风向为东南风、西南风。  相似文献   

滇西陇川断陷盆地地热水化学特征及循环过程     

黄琴辉  张华  康晓波  王波  刘海峰  柴金龙  黄钊  王燕 《中国岩溶》2020,39(6):793-801

通过对陇川盆地开展地热地质调查，查清其地热资源分布:盆地内共出露地热点11处，热储结构类型为带状型和层状型，盆地中部为层状型，两侧盆地边缘为带状型，其中北西部受断裂控制明显，南东部受节理裂隙控制明显。其储热层为变质岩及新近系芒棒组的花岗质砂砾岩、细砂岩；地热水受大气降水影响明显，循环深度都在1 600 m以上，大部分在1 800~2 400 m之间，主要来源于深部热源，通过断裂、裂隙及砂砾石孔隙作为导水、储水上涌通道，接收来自山区补给的地下水混合出露于地表，补给距离在1.5 km以上，如南宛河温泉温度最高，地下水循环深度最深，补给距离最远，达10 km；盆地北东和西部水温高，循环深度深。   相似文献   

The southern Norwegian Sea during the last 45 ka: hydrographical reorganizations under changing ice‐sheet dynamics     

《第四纪科学杂志》2017,32(7):908-922

  相似文献   

A note on the consolidation settlement of a rigid circular foundation on a poroelastic halfspace          下载免费PDF全文

Jueun Kim  A.P.S. Selvadurai 《国际地质力学数值与分析法杂志》2016,40(14):2003-2016

This paper uses Biot's poroelasticity approach to examine the consolidation behaviour of a rigid foundation with a frictionless base in contact with a poroelastic halfspace. The mathematical development of the mixed boundary value problem involves a set of dual integral equations in the Laplace transform domain which cannot be conveniently solved by employing conventional procedures. In this paper, a numerical solution is developed using a scheme where the contact normal stress is approximated by a discretized equivalent. The influence of limiting drainage boundary conditions at the entire surface of the halfspace on the degree of consolidation of the rigid circular foundation is investigated. The results obtained in this study are compared with the corresponding results given in the literature. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

One‐dimensional dynamics of saturated incompressible porous media: analytical solutions and influence of inertia terms          下载免费PDF全文

Yunpeng Zhang  Dorival M. Pedroso  Wolfgang Ehlers 《国际地质力学数值与分析法杂志》2016,40(18):2489-2513

The complexity of formulations for the hydromechanical coupled mechanics of porous media is typically minimised by simplifying assumptions such as neglecting the effect of inertia terms. For example, three formulations commonly employed to model practical problems are classified as fully dynamic, simplified dynamic and quasi‐static. Thus, depending on the porous media conditions, each formulation will have advantages and limitations. This paper presents a comprehensive analysis of these limitations when solving one‐dimensional fully saturated porous media problems in addition to a new solution that considers a more general loading situation. A phase diagram is developed to assist on the selection of which formulation is more appropriate and convenient regarding particular cases of porosity and hydraulic conductivity values. Non‐dimensional formulations are proposed to achieve this goal. Results using the analytical solutions are compared against numerical values obtained with the finite element method, and the effect of porosity is investigated. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Tests and applications of an approach to absorbing reflected waves towards incident boundary     

张洪生  王炎  许春辉  商辉  于小伟 《中国海洋工程》2013,27(6):703-718

If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary.  相似文献   

An iterative pressure‐stabilized fractional step algorithm in saturated soil dynamics     

Xikui Li  Xue Zhang  Xianhong Han  D. C. Sheng 《国际地质力学数值与分析法杂志》2010,34(7):733-753

This paper presents an iterative, incremental pressure‐stabilized fractional step algorithm for coupled hydro‐mechanical problems with mixed formulations of the displacement–pressure ( u –p) model in saturated soil dynamics that allows the use of finite elements with equal low order of interpolation approximation of u and p. In comparison with the original fractional step algorithm, the distinct features of the proposed algorithm lie in its enhanced stability owing to the introduction of both an iteration procedure and a finite increment calculus (FIC) process into the algorithm. The introduction of the iterative procedure makes the velocity term satisfy the momentum conservation equation in an implicit sense and allows much larger time step sizes to be used than those limited in existing explicit and semi‐implicit versions of the algorithm. The introduction of the FIC process removes the dependence of the stability of the proposed algorithm on the time step size, as a result it allows to using the incremental version of the algorithm and evades the minimum time step size requirement presented in the existing versions of the fractional step algorithm that restricts the application of the algorithm to saturated soil dynamics problems with high frequencies. Numerical experiments demonstrate the effectiveness and improved performance of the proposed iterative pressure‐stabilized fractional step algorithm. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Seasonal rainfall–runoff relationships in a lowland forested watershed in the southeastern USA     

Ileana B. La Torre Torres  Devendra M. Amatya  Timothy J. Callahan 《水文研究》2011,25(13):2032-2045

Hydrological processes of lowland watersheds of the southern USA are not well understood compared to a hilly landscape due to their unique topography, soil compositions, and climate. This study describes the seasonal relationships between rainfall patterns and runoff (sum of storm flow and base flow) using 13 years (1964–1976) of rainfall and stream flow data for a low‐gradient, third‐order forested watershed. It was hypothesized that runoff–rainfall ratios (R/P) are smaller during the dry periods (summer and fall) and greater during the wet periods (winter and spring). We found a large seasonal variability in event R/P potentially due to differences in forest evapotranspiration that affected seasonal soil moisture conditions. Linear regression analysis results revealed a significant relationship between rainfall and runoff for wet (r² = 0·68; p < 0·01) and dry (r² = 0·19; p = 0·02) periods. Rainfall‐runoff relationships based on a 5‐day antecedent precipitation index (API) showed significant (r² = 0·39; p < 0·01) correspondence for wet but not (r² = 0·02; p = 0·56) for dry conditions. The same was true for rainfall‐runoff relationships based on 30‐day API (r² = 0·39; p < 0·01 for wet and r² = 0·00; p = 0·79 for dry). Stepwise regression analyses suggested that runoff was controlled mainly by rainfall amount and initial soil moisture conditions as represented by the initial flow rate of a storm event. Mean event R/P were higher for the wet period (R/P = 0·33), and the wet antecedent soil moisture condition based on 5‐day (R/P = 0·25) and 30‐day (R/P = 0·26) prior API than those for the dry period conditions. This study suggests that soil water status, i.e. antecedent soil moisture and groundwater table level, is important besides the rainfall to seasonal runoff generation in the coastal plain region with shallow soil argillic horizons. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Lake Ladoga ice phenology: Mean condition and extremes during the last 65 years     

Sergey Karetnikov  Mikhail Naumenko 《水文研究》2011,25(18):2859-2867

Winter conditions play an important role for the largest lake in Europe—Lake Ladoga. The ice cover lasts for 171 ± 3 days on average from the early November until the mid‐May. We investigated the ice regime of Lake Ladoga using a constructed ice database of aircraft surveys and satellite images. More than 1250 surveys of the lake's ice cover from 1943 to 2010 were collected and analysed to determine mean and extreme ice conditions for winters of different types of severity. The time series of ice cover percentage over the lake was plotted. On average, 18 observational ice charts were made every winter. Individual ice phenology records show considerable year‐to‐year variation. For this reason, records typically have been combined and analysed as groups (categories). Extremely cold winters were determined as winters with complete ice cover that lasts more than three months which is approximately 90% quartiles from all winters with complete ice cover. The lake surface was completely covered with ice for more than three months during 5 seasons. Extremely warm winters when the maximum ice cover was less than 70% of the lake area occurred during 5 seasons as well. A basic relationship between the winter severity as winter maximum of accumulated freezing degree‐days (AFDD) and the earlier derived Relative Ice Cover Index (RICI) was established. We have used teleconnection indices such as North Atlantic Oscillations (NAO) and Arctic Oscillation (AO) for the period from October to May for estimation of different types of Lake Ladoga's ice conditions. The AO index in winter months and local winter maximum of AFDD explained much of the interannual variation in ice cover. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

2015-2018年海南省臭氧污染特征及其天气类型     

符传博  丹利  徐文帅  刘丽君 《气象与环境学报》2021,37(6):27-35

根据2015—2018年海南省18个市县32个空气质量监测站O₃浓度资料,分析了区域性O₃污染（O₃-8h浓度超标市县≥3个）时空变化特征,并对造成O₃污染的天气系统进行主观分型。结果表明：2015—2018年海南省共有40 d发生了区域性O₃污染,发生概率为2.73%。其中2015年和2017年达到了13 d,发生概率为3.56%,2018年为11 d（3.01%）,2016年仅为3 d（0.82%）。发生区域性O₃污染主要有4种天气类型：冷空气偏西下型、冷空气偏东下型、变暖高压脊型和热带系统型。其中冷空气偏西下型是最主要的天气类型,共出现了14 d,占所有天数的35%,且污染较重。不同天气类型下海南省O₃污染表现出不同的分布特征。500 hPa有下沉气流、低层受东北风控制,有相对湿度低值区从中国东部向海南省延伸,地面位于冷高压底部或热带气旋西北侧,温度露点差在5 ℃以上等条件均有利于海南省区域性O₃污染天气出现。  相似文献