Study of forward–backward solute dispersion profiles in a semi-infinite groundwater system

ABSTRACT

Forward–backward solute dispersion with an intermediate point source in one-dimensional semi-infinite homogeneous porous media is studied in this paper. Solute transport under sorption conditions, first-order decay and zero-order production terms are included. The first type of boundary condition is taken as a constant point source at an intermediate point from where forward and backward solute dispersion is examined. The Laplace transform method is adopted to solve the governing equation analytically. All the analytical results are obtained in graphical form to investigate the forward–backward solute transport in porous media for various hydrological input data. The graphical nature of the analytical solution is compared with numerical data taken from existing literature and similar results are obtained. Also, numerical solution of the governing equation is obtained by the Crank-Nicolson finite difference scheme and validated with the analytical solution, which demonstrates good agreement between them. Accuracy of the solution is also observed by using RMSE.     

一种基于温度历史和瞬态地温场模拟的剥露历史反演方法

根据低温热年代学数据,提取岩石从深部剥露到地表的信息,对理解诸多地质问题(如造山带演化、地表过程及其相互作用等)具有重要意义.本文提出一种基于岩石温度历史(可利用古温标、热年代计等方法制约),并考虑剥露过程对地温场扰动的剥露历史反演计算方法.基于假定的与真实数据的正反演模拟和参数敏感性分析表明:热扩散率的变化对剥蚀量计算影响不大,在常规岩石热扩散率变化范围内(20～35km2/Ma),总剥蚀量变化小于10%;传统计算方法低估了剥蚀总量,对于现今地温梯度小于20℃/km、冷却速率大于2～3℃/Ma,或现今地温梯度大于30℃/km、冷却速率大于5～10℃/Ma的地区,需要考虑热平流对剥蚀量计算的影响;匀速冷却的热历史指示剥蚀速率持续减小,而非匀速剥蚀.本文将该方法应用到龙门山南段和四川盆地,反演计算显示龙门山南段15Ma以来的剥蚀总量为8km,四川盆地中部80Ma以来剥蚀总量约为3km、东部约5km.     

中南地区一次飞机颠簸的物理量场分析

利用ERA-interim再分析资料和中南地区航空器空中报告,分析2017年2月4日20:00前后的颠簸报告位置与物理量场分布特征,结果表明:与颠簸位置对应最好的是散度场的强梯度区和温度平流的等零度线两侧,靠近涡度大值中心的强梯度区和垂直速度的大值区或大梯度区附近也容易发生颠簸,若满足以上条件的物理量场达3个或以上的区...     

四川盆地2020年“8.11”特大暴雨过程中尺度系统演变特征

针对2020年8月11—12日四川盆地西部特大暴雨过程中尺度系统演变特征和维持机制,利用欧洲中心ERA5逐小时再分析资料以及FY-4A的云顶相当黑体温度TBB资料进行诊断分析。(1)本次过程发生在500 hPa巴湖长波槽分裂短波和高原低槽东移发展在四川盆地停滞,副高加强西伸形成阻挡的形势下,同时200 hPa有南亚高压和高空分流区配合。(2)在上述有利的背景条件下,中尺度系统活动经历了中尺度辐合扰动-西南涡生成发展-低空急流影响-西南涡再次发展增强等4个阶段,西南涡两个阶段的发展对降水影响最大,初生发展阶段雨强最强,再次发展阶段强降雨范围最大。(3)西南涡在暖区内初生发展,对流不稳定性强,地面潜热和感热加热以及500 hPa层以下水汽凝结潜热加热均十分显著,在较强暖湿平流作用下,配合低层涡度拉伸项和扭转项的动力作用加强,西南涡迅速发展,但低层辐合相对较弱,正涡度柱高度仅发展至500 hPa。(4)西南涡再次发展阶段冷平流入侵,大气斜压性增强,中高层感热和凝结潜热加热作用加大,“低层辐合-中高层辐散”的动力机制显著加强,配合垂直向上输送正涡度和涡度拉伸项的动力发展作用,西南涡发展旺盛,正...     

阿拉伯海东南海域盐度收支的季节变化

采用SODA海洋同化产品的月平均资料,本文分析了阿拉伯海东南海域表层盐度的季节变化特征,发现局地海面淡水通量不能解释盐度的变化。两个典型区域的表层海水盐度收支分析表明,海洋的平流输送是造成阿拉伯海东南海域盐度冬季降低、夏季升高的主要原因,而淡水通量仅在夏季印度西侧沿岸区域造成盐度降低。冬季,东北季风环流将孟加拉湾北部的低盐水沿同纬度输送到阿拉伯海,然后向北输送,使表层海水盐度降低;夏季,西南季风环流把阿拉伯海西北部的高盐水向南、向东输送,使阿拉伯海东南海域盐度升高。受地理位置因素的影响,阿拉伯海东南海域表层盐度的变化冬季明显强于夏季。     

On the performance of surface renewal analysis to estimate sensible heat flux over two growing rice fields under the influence of regional advection

High-frequency temperature data were recorded at one height and they were used in Surface Renewal (SR) analysis to estimate sensible heat flux during the full growing season of two rice fields located north–northeast of Colusa, CA (in the Sacramento Valley). One of the fields was seeded into a flooded paddy and the other was drill seeded before flooding. To minimize fetch requirements, the measurement height was selected to be close to the maximum expected canopy height. The roughness sub-layer depth was estimated to discriminate if the temperature data came from the inertial or roughness sub-layer. The equation to estimate the roughness sub-layer depth was derived by combining simple mixing-length theory, mixing-layer analogy, equations to account for stable atmospheric surface layer conditions, and semi-empirical canopy–architecture relationships. The potential for SR analysis as a method that operates in the full surface boundary layer was tested using data collected over growing vegetation at a site influenced by regional advection of sensible heat flux. The inputs used to estimate the sensible heat fluxes included air temperature sampled at 10 Hz, the mean and variance of the horizontal wind speed, the canopy height, and the plant area index for a given intermediate height of the canopy. Regardless of the stability conditions and measurement height above the canopy, sensible heat flux estimates using SR analysis gave results that were similar to those measured with the eddy covariance method. Under unstable cases, it was shown that the performance was sensitive to estimation of the roughness sub-layer depth. However, an expression was provided to select the crucial scale required for its estimation.     

Study of Dynamical Structure of an Unusual Monsoon Depression formed over the Bay of Bengal during August 2006

Monsoon depressions, the main rain-producing systems over the Indian region along and near their tracks, are found to intensify the monsoon circulation by organizing low-level convergence. The normal track of the monsoon depressions is along the position of the monsoon trough at the surface, i.e., northwestward from the Head Bay of Bengal. Most of the monsoon depressions dissipate within one or two days after landfall. An unusual monsoon depression formed in the Bay of Bengal during the 1^st week of August 2006 causing heavy to very heavy rainfall over Madhya Pradesh, Maharashtra and Gujarat States of India. The track of this depression was anomalously southward from the mean track of the August depressions. It maintained its intensity during its longer travel. This paper addresses some of the dynamical characteristics of the depression in relation to its southward/westward track and longer travel. It is observed that horizontal advection of absolute vorticity above 550 hPa (below 600 hPa) along west (east) of the depression and maximum divergence of absolute vorticity below 400 hPa dominated for the westward movement of the depression. Increased moisture supply from the Arabian Sea (after the landfall of the depression) helped to maintain the intensity of the system throughout its long travel. The energy conversion terms revealed the strengthening of the zonal flow at higher levels prior to the formation of the depression.     

互补相关理论在卫星遥感领域的应用研究

由于地球各种运动和纬度的不同,使能量的分布在时间和空间上明显不均一,导致大气、海洋、冰雪层、陆地和生物发生重大变化。在某些时间尺度上,此种影响的重要性甚至超过太阳活动本身变化对于地球系统的影响。地表温度、地表反照率、潜热交换是刻划地气系统能量交换的３个重要参数,以中国华北地区为例,将互补相关理论应用于遥感领域,应用ＮＯＡＡ／ＡＶＨＲＲ气象卫星资料,对互补相关模式中所需的反照率、表面温度,完全应用遥感数据反演;对互补相关理论中涉及到的大尺度平流参数、Ｐｅｎｍａｎ分式、辐射项等因子进行了订正,并将互补相关理论应用于流域、湖泊、区域农田蒸发的计算中。     

Stream bed temperature profiles as indicators of percolation characteristics beneath arroyos in the Middle Rio Grande Basin,USA

Stream bed temperature profiles were monitored continuously during water year 1990 and 1991 (WY90 and 91) in two New Mexico arroyos, similar in their meteorological features and dissimilar in their hydrological features. Stream bed temperature profiles between depths of 30 and 300 cm were examined to determine whether temporal changes in temperature profiles represent accurate indicators of the timing, depth and duration of percolation in each stream bed. These results were compared with stream flow, air temperature, and precipitation records for WY90 and 91, to evaluate the effect of changing surface conditions on temperature profiles. Temperature profiles indicate a persistently high thermal gradient with depth beneath Grantline Arroyo, except during a semi-annual thermal reversal in spring and autumn. This typifies the thermal response of dry sediments with low thermal conductivities. High thermal gradients were disrupted only during infrequent stream flows, followed by rapid re-establishment of high gradients. The stream bed temperature at 300 cm was unresponsive to individual precipitation or stream flow during WY90 and 91. This thermal pattern provides strong evidence that most seepage into Grantline Arroyo failed to percolate at a sufficient rate to reach 300 cm before being returned to the atmosphere. A distinctly different thermal pattern was recorded beneath Tijeras Arroyo. Low thermal gradients between 30 and 300 cm and large diurnal variations in temperature, suggest that stream flow created continuous, advection-dominated heat transport for over 300 days, annually. Beneath Tijeras Arroyo, low thermal gradients were interrupted only briefly during periodic, dry summer conditions. Comparisons of stream flow records for WY90 and 91 with stream bed temperature profiles indicate that independent analysis of thermal patterns provides accurate estimates of the timing, depth and duration of percolation beneath both arroyos. Stream flow loss estimates indicate that seepage rates were 15 times greater for Tijeras Arroyo than for Grantline Arroyo, which supports qualitative conclusions derived from analysis of stream bed temperature responses to surface conditions. © 1997 John Wiley & Sons, Ltd.     

2016～2017年凌汛期黄河内蒙河段快速封河的天气成因分析

利用常规观测资料,对2016年11月2023日内蒙河段强降温天气过程进行诊断分析。结果表明:造成这次快速封河的强降温天气过程,与贝湖附近的横槽转竖密切相关。500h Pa上由里海到西西伯利亚平原上空有高压脊强烈发展,脊崩溃是横槽转竖及强冷空气向南爆发的预报着眼点。随着高空横槽转竖并南下,从地面冷高压主体分裂出来的小高压不断东移南下影响内蒙河段。低层冷槽在移动过程中不断加强,并在偏北风急流作用下产生强冷平流,加剧了内蒙河段的温度梯度,共同造成了本次内蒙河段强冷空气天气过程。当北西伯利亚低地出现大量冷空气堆积,且有典型天气形势配合冷空气活动时,要考虑内蒙地区将有强降温过程;如遇内蒙河段河道流量较小,在沿河各站48h降幅达到寒潮标准,最大降幅在14℃以上时,要考虑内蒙河段从流凌到封河的历时将会较短。