The distribution of methane in the Tōkyō-wan

Eleven stations were occupied in the Tokyo-wan during a study on the distribution of methane in this autrophic coastal environment in August of 1993.The principal features of the observed methane included the following 6 points: (1) Excess methane in the surface layer from 1.5 times to greater than 25 times solubility equilibrium with the atmosphere.(2) The methane concentration in the upper water displayed a maximum wne around Station 5 and the second highest in bottom water at Stations 1 and 2,probably because there was the front resulting from the chemical processes.(3) Cotrelations between methane and other parameters exhibited correspondences and the methane distribution being mainly controlled by physical processes.(4) In some'stations,vertical profiles revealed associations between methane and Chl a and the relationships between methane with Chl a or nitrite have shown good linear cortelations.It is postulated that some methane is formed in situ.(5) The calculated flux of methane acrbss the air-sea interface was about 71 μmol/(m²·d).(6) Some methane might be produced along with the organic matter decomposition in bottom water.Others might be due to the methane fluxes into the bottom water from the anoxic sediment inside the bay,which are believed to be the main methane source.     

A finite volume solution of wave forces on submarine pipelines

In this paper, a numerical model is established for simulating the wave forces on a submarine pipeline. A set of two-dimensional Navier–Stokes equations is discretized numerically with a finite volume method in a moving mesh system. After each time step, the mesh is modified according to the changed wave surface boundary. The deffered correction second-order upwind scheme (SUDC) is adopted here to discretize the convective fluxes. The effects of the clearance between the pipeline and the seabed, water depth and wave height on wave forces are studied, respectively. The results by the numerical simulation agree well with the experimental data and theory value.     

第六次南极考察—长城站越冬气象考察报告

本文以中国第六次南极考察队在长城站观测到的气象资料与历史资料对照分析,介绍了长城站的天气特征,如气旋的来源、移动规律,海雾的特点,降水情况,特别是夏季的降水情况。较详细地介绍了1990年长城站的天气状况。 总结了长城站气压、风、气温、云、日照、降水及蒸发等项目的观测工作。对关城站的天气预报工作也作了总结,特别是极地气旋的预报和各天气要素的预报方法。并以1990年1月16日营救遇暴风雪的考察队员预报为实例,介绍了一次成功的预报。     

Wave-Induced Seepage Force Acting on Cylinder Groups

Wave-induced seepage force acting on cylinder groups is studied by using Biot consolidation theory in this paper. Both tandem arrangement and side by side arrangement are considered simultaneously. The variations of the coefficient of grouping effect with the distance between cylinders for different KD are discussed. In order to verify the numerical solution, several sets of experiments are conducted. The agreement between numerical and experimental solutions is satisfactory.     

A summary of seismic activities in and around China in 2021

In this article, we review the general characteristics of seismicity in and around China and the overall statistics of earthquake damage in 2021, focusing on several significant events and related scientific topics. Among them, the largest event is the M_S 7.4 Madoi earthquake in Qinghai Province, northwest China. The event marks another M_S ?≥ ?7 earthquake occurring near the boundary of the Bayan Har Block that has ended a remarkable quiescence of the M_S ?≥ ?7 earthquakes within the Chinese mainland. In addition, the M_S 6.4 Yangbi earthquake in Yunnan Province, southwest China draws the most attention because of its abundant foreshocks, which are well recorded by the densely distributed seismic stations in the surrounding regions. Regarding this event, we review several recent publications focusing on the Gutenberg-Richter b-value change and the physical mechanism of foreshocks associated with this sequence. The M_S 6.0 Luxian earthquake in Sichuan Province, southwest China has caused serious damage with a relatively low magnitude, partly because the focal depth of the mainshock is relatively shallow (3.5 ?km). It is another strong earthquake occurring within the southeast Sichuan basin with low historical seismicity yet has increased significantly since 2015, probably due to shale gas development and associated hydraulic fracturing.     

黄渤海有机碳的分布特征及收支评估研究

陆架边缘海是陆海相互作用研究中最为关键的区域,也是全球重要的碳储库,在区域物质循环过程中发挥着重要的作用。基于2012年5月和11月对黄渤海海域的综合调查,对该海域水体和沉积物中有机碳的含量与分布进行了分析,并结合相关文献资料对黄渤海有机碳的收支进行了估算。主要结论为:黄渤海溶解有机碳和颗粒有机碳均呈近岸河口区域高、离岸低的分布趋势;有机碳的组成以溶解有机碳为主,颗粒有机碳由海洋自生的有机碳和陆地来源的有机碳组成;黄渤海沉积物有机碳高值区主要分布在河口和泥质区,其组成也是由海洋自生和陆源混合而成,其中渤海以陆源为主,而黄海以海源为主。黄渤海有机碳收支评估表明,有机碳的主要来源为初级生产力产生的有机物,其贡献为(6 760±971)×104t/a,占有机碳输入总量的(74±10)%,沉积物再悬浮的通量为(884±200)×104t/a,东海向黄海输入的通量为(679±107)×104t/a,河流及陆源输入的通量为(643±63)×104t/a,大气干湿沉降的通量为(141±39)×104t/a,其贡献分别占有机碳输入总量的(10±2.2)%,(7.5±1.2)%,(7.0±0.7)%和(1.5±0.4)%;黄渤海有机碳的主要支出为呼吸消耗,其贡献为(5 190±746)×104t/a,占有机碳输出总量的(57±8.2)%,黄海向东海输出的通量为(2 150±370)×104t/a,有机碳沉积通量为(1 030±225)×104t/a,有机碳降解通量为(737±191)×104t/a,其贡献分别占有机碳输出总量的(24±4.1)%,(11±2.5)%和(8.0±2.1)%。有机碳收支评估表明黄渤海有机碳以海洋自生来源为主,且具有潜在碳的"汇"的特性,水体中外源输入和海洋自生有机碳的(1.6±0.3)%埋藏于该海域内。     

A numerical model for onset of scour below offshore pipelines

A numerical model is developed to predict the onset of local scour below offshore pipelines in steady currents and waves. The scour is assumed to start when the pressure gradient underneath the pipeline exceeds the floatation gradient of the sediments. In this model, the water flow field above the bed is determined by solving the two-dimensional (2-D) Reynolds-averaged Navier–Stokes equations with a k-ω turbulence closure. The seepage flow below the seabed is calculated by solving the Darcy's law (Laplace's equation) with known pressure distribution along the common boundaries of the flow domains-seabed. The numerical method used for both the turbulent flow around the pipeline and Darcy's flow in the seabed is a fractional finite element method. The average pressure gradient along the buried pipe surface is employed in the evaluation of onset condition with a calibration coefficient. The numerical model is validated against experimental data available in literature. A unified onset condition for steady currents and waves is proposed. Influences of flow parameters, including water depth, embedment depth, boundary layer thickness, Reynolds number (Re) and Keuleagan–Carpenter (KC) number, on the pressure drop coefficient over the pipeline are studied systematically.     

Numerical simulation of non-linear regular and focused waves in an infinite water-depth

Inviscid three-dimensional free surface wave motions are simulated using a novel quadratic higher order boundary element model (HOBEM) based on potential theory for irrotational, incompressible fluid flow in an infinite water-depth. The free surface boundary conditions are fully non-linear. Based on the use of images, a channel Green function is developed and applied to the present model so that two lateral surfaces of an infinite-depth wave tank can be excluded from the calculation domain. In order to generate incident waves and dissipate outgoing waves, a non-reflective wave generator, composed of a series of vertically aligned point sources in the computational domain, is used in conjunction with upstream and downstream damping layers. Numerical experiments are carried out, with linear and fully non-linear, regular and focused waves. It can be seen from the results that the present approach is effective in generating a specified wave profile in an infinite water-depth without reflection at the open boundaries, and fully non-linear numerical simulations compare well with theoretical solutions. The present numerical technique is aimed at efficient modelling of the non-linear wave interactions with ocean structures in deep water.