Observations And Modelling Of The On-Ice And Off-Ice Air Flow Over The Northern Baltic Sea

Two cases of on-ice and off-ice air flow characterizing the opposite weather situations over the ice-edge zone in the northern Baltic Sea are analysed on the basis of aircraft observations, and modelled using atwo-dimensional mesoscale model. The stable boundary layer (SBL) during theon-ice flow exhibited little thermal modification, but a low-level jet (LLJ) was generated at the 250-m high top of the SBL. In the model, the LLJ was associated with inertial oscillations in space, while the baroclinicity explained the shape of the wind profile well above the SBL. Although the observed LLJ was most pronounced over the ice, the modelling suggests that it was not generated by the ice edge but by the coastline some 400 km upwind of the ice edge, where a much more drastic change in the thermal stratification and surface roughness took place. The generation, maintenance, and strength of the LLJ were very sensitive to the parameterization of turbulent mixing in the SBL. In the case of the off-ice flow, the modification of the air mass and the development of a convective boundary layer (CBL) both over the ice and open sea were reasonably well modelled. Sensitivity runs suggested that it was essential to take into account the effects of subgrid-scale leads, a forest in the archipelago (which was crossed by the air flow), and water vapour condensationinto ice crystals. The heat flux from leads was particularly important for the heatbudget of the CBL, and the observed growth of the CBL was partly due to theeffective mixing over the rough and relatively warm forest.     

鄂西火烧坪地区岩溶生态环境系统及生态农业模式初探

通过对鄂西火烧坪地区的自然地理、地质构造、水文地质、土壤、植被及社会经济等方面的初步研究表明，在岩溶化作用十分强烈的岩溶山区，当气候、地形地貌、地质构造等条件匹配较好时，同样存在着一些极其有利于农业、林业发展的特殊生态环境。在这些地区，结合当地植物资源特点和市场需求，通过农作物类型的调整，能够在短时间内使当地摆脱贫穷的面貌。但在发展经济的同时必须特别关注当地土地资源相对缺乏、水资源时空分布不均、生态环境脆弱等不利因素，做到适度开发，稳步发展，才能从根本上实现小康目标。     

长江三峡工程奉节库岸边坡地下水渗流场模拟分析

长江三峡工程正常蓄水位为175m，在蓄水过程中随着库水位的抬升，必然会引起库岸边坡地下水渗流场的变化。运用3D－Modflow软件模拟了三峡工程的蓄水过程中奉节库段边坡岩土体内部地下水位的动态变化，为长江三峡工程奉节库区段移民迁建地质灾害预测与防治提供科学依据。     

黑龙江省矿区生态破坏与地质灾害及其防治

黑龙江省矿产分布情况和开发概况以及矿业开发在经济发展中占有重要地位 ;在矿业开发过程中引起的诸多生态破坏和地质灾害及其引起的危害 ,已引起高度重视 ;本文在综合论述黑龙江省矿区发展所带来各项利弊后提出了具体的防治对策。     

欧北-大湾地区火山岩储层成因机制的研究

从分布、成分组成、形成机制等几个方面探讨了辽河油田东部凹陷中段最主要的火山岩储层－－粗面岩的成因机制，并对其成为该区良好储层的原因进行了探讨，通过对比说明了另一类火山岩－－玄武岩不含油的原因，并建立了成因模式，最后得出结论：粗面岩呈喷发状态产出，由于其硅质含量高，流动性小，容易在构造高部位形成巨厚的火山岩锥或火山岩钏，从而造成其大部分在水上，结晶较好且储层物性极佳，同时因其裂缝发育，这些因素结合起来使其成为良好的会层。从供油方式来看，其成藏方式属于侧生式，而从生储盖组合方式来看，其属于自生、自储、自盖式成藏组合。同时给出了其成藏模式。     

基于栅格空间信息定量化的湖南西部地区生态环境综合评价

以湖南西部地区为研究区域,采用遥感影像作为主要数据源,针对区域主要生态问题,利用栅格数据结构为主的数字环境模型,建立了生态环境质量综合评价模型. 对区域生态环境质量的空间分异格局进行了研究,通过将评价结果与数字高程模型迭加分析,研究了生态环境质量的垂直地带性分布规律,探索适合以山高坡陡为主要地貌特征的山区生态评价方法,结果显示,湖南西部地区生态环境综合指数呈正态分布,大部分地区环境质量属一般. 总体环境状况东南部好于西北部,河谷盆地优于山地. 研究表明,利用遥感和地理信息系统技术进行区域生态环境评价,具有数据采集快速、客观,评价和制图自动化,评价结果空间定位精度高,直观性与实用性强等优点.     

天山奎屯河哈希勒根51号冰川表面运动特征分析

奎屯河哈希勒根51号冰川位于新疆奎屯市以南的天山依连哈比尔尕山北坡, 奎屯河上游支沟哈希勒根河源区. 1999年8月, 在该冰川上布设了用于冰川运动和冰川物质平衡观测研究的测杆18根, 并进行了冰川表面运动、冰川物质平衡和冰川末端变化的首次观测. 根据2000年8月和2001年8月的冰川运动观测资料, 分析了奎屯河哈希勒根51号冰川的运动特征和冰舌末端的变化状况. 结果表明: 奎屯河51号冰川应属于亚大陆型冰川; 1999/2000年度和2000/2001年度的表面运动值不大, 最大流速点的年运动速度为3.15 ma-1; 运动速度垂直分量UZ的变化规律同乌鲁木齐河源1号冰川的变化规律相同, 即消融区的显出流作用和积累区的显入流作用. 该冰川的冰舌末端处于相对稳定的退缩状态, 1964-1999年间平均退缩量约为1.4 m*a-1, 而1999-2001年间的平均退缩量为5.0 m*a-1, 反映出冰川退缩增大的趋势.     

离散裂隙渗流方法与裂隙化渗透介质建模

流体渗流模拟的连续介质方法通常适用于多孔地质体，并不一定适用于裂隙岩体，由于裂隙分布及其特征与孔隙差异较大。若流体渗流主要受裂隙的控制，对于一定尺寸的裂隙岩体，多孔介质假设则较难刻划裂隙岩体的渗流特征。离散裂隙渗流方法不但可直接用于模拟裂隙岩体非均质性和各向异性等渗流特征，而且可用其确定所研究的裂隙岩体典型单元体及其水力传导（渗透）张量大小。主要讨论了以下问题：（1）饱和裂隙介质中一般的离散流体渗流模拟；（2）裂隙岩体中的REV（典型单元体）及其水力传导（渗透）张量的确定；（3）利用离散裂隙网络流体渗流模型研究裂隙方向几何参数对水力传导系数和REV的影响；（4）在二维和三维离散裂隙流体渗流模型中对区域大裂隙和局部小裂隙的处理方法。调查结果显示离散裂隙流体渗流数学模型可用来评价不同尺度上的裂隙岩体的水力特征，以及裂隙方向对裂隙化岩体的水力特征有着不可忽视的影响。同时，局部小裂隙、区域大裂隙应当区别对待，以便据其所起的作用及水力特征，建立裂隙化岩体相应的流体渗流模型。     

Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico

The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity. Electronic Publication     

Analogue study of particle segregation in pyroclastic density currents, with implications for the emplacement mechanisms of large ignimbrites

Abstract Analogue flume experiments were conducted to investigate the transport and sedimentation behaviour of turbulent pyroclastic density currents. The experimental currents were scaled approximately to the natural environment in three ways: (1) they were fully turbulent; (2) they had a very wide range of particle sizes and associated Rouse numbers (the ratio of particle settling velocity to effective turbulent eddy velocity in the current); and (3) they contained particles of two different densities. Two sets of surge‐type experiments were conducted in a 5 m long, water‐filled lock‐exchange flume at five different volumetric particle concentrations from 0·6% to 23%. In one set (one‐component experiments), the currents contained just dense particles; in the other set (two‐component experiments), they contained both light and dense particles in equal volume proportions. In both sets of experiments, the population of each component had a log‐normal size distribution. In the two‐component experiments, the size range of the light particle population was selected in order to be in hydrodynamic equivalence with that of the dense particles. Dense particles were normally graded, both vertically and downstream, in the deposits from both sets of experiments. The mass loading (normalized to the initial mass of the suspension) and grain size of the dense component in the deposits decreased with distance from the reservoir and were insensitive to initial total particle concentration in the currents. On the other hand, in the two‐component experiments, the light particles were extremely sensitive to concentration. They were deposited in hydrodynamic equivalence with the dense particles from dilute currents, but were segregated efficiently at concentrations higher than a few per cent. With increasing particle concentration, the large, light particles were carried progressively further down the flume because of buoyancy effects. Deposits from the high‐concentration currents exhibited reverse vertical grading of the large, light particles. Efficient segregation of the light component was observed even if the bulk density of the current was less than that of the light particles. In both sets of experiments, marked inflexions in the rate of downstream decline in mass loading and maximum grain size of the dense component can be attributed to the presence of two different particle settling regimes in the flow: (1) particles with Rouse numbers >2·5, which did not respond to the turbulence and settled rapidly; and (2) particles with Rouse numbers <2·5, which followed the turbulent eddies and settled slowly. The results are applied to the transport and sedimentation dynamics of pyroclastic density currents that generate large, widespread ignimbrites. Field data fail to reveal significant departures from aerodynamic equivalence between pumice and lithic clasts in three such ignimbrites: the particulate loads of some large ignimbrites are transported principally in turbulent suspensions of low concentration. In some ignimbrites, the well‐developed inflexions in curves of maximum lithic (ML) size vs. distance can be attributed to the existence of distinct high and low Rouse number particle settling regimes that mark the transition from an overcharged state to one in which the residual particulate load is transported more effectively by turbulence.