The impact of highly permeable layer on hydraulic system in a coastal aquifer     

Kue‐Young Kim  Weon Shik Han  Eungyu Park 《水文研究》2013,27(22):3128-3138

This study is aimed to understand the hydraulic mechanism of coastal aquifer systems that include highly permeable layers (HPLs). These hydrologic conditions can be found in many volcanic islands that are composed of a series of lava flows discharged into sea or other standing body of water. In the first part, we developed a numerical model based on the geologic and hydrologic data obtained from the eastern Jeju Island, Korea, of which the aquifer contains clinker and hyaloclastite layers. The simulation results reproduced spatial location of fresh‐saline water interface, especially the abrupt decline of interface at the inland part and the thickness variation of transition zone along the cross‐section observed at the eastern Jeju coastal aquifer. We were able to find out that these phenomena are strongly related to the presence of the HPL. In the second part, quantitative analyses were conducted with the use of hypothetical models in order to understand the dynamic characteristics of coastal system that includes HPLs. A series of sensitivity studies were conducted to assess the effect of the horizontal length and vertical depth of HPL on the spatial location of the interface toe and the configuration of transition zone. Various case studies have shown that the seawater intruded into the inland more as the horizontal length of HPL was increased and its vertical depth was decreased. In other simulations including two HPLs, the vertical distance between these two HPLs primarily controlled the flow regime, flux variations, and the configuration of the transition zone. Finally, we performed simulations to evaluate the effect of a rising sea‐level. This study provides more understanding of how the presence of HPL controls the seawater intrusion processes, and the spatial configurations of fresh‐saline water interface at coastal aquifers. Copyright © 2012 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   

Low-velocity structure beneath Africa from forward modeling   总被引：1，自引：0，他引：1  

Sidao Ni  Xiaoming Ding  Donald V Helmberger  Michael Gurnis 《Earth and Planetary Science Letters》1999,170(4):21-507

Seismic waveforms observed in South Africa containing the first arrival crossover of S to SKS (70° to 110°) are analyzed. The data consist of analog records from the World Wide Seismographic Station Network (WWSSN) of deep events beneath South America. The S-waves arrive 2 to 3 s early relative to PREM at ranges from 70° to 95° and then become increasingly delayed, becoming 5 to 6 s late at 110°. The SKS phase is late by 3 to 5 s over the entire range. This pushes crossover between S and SKS, normally observed at about 81°, out about 2° to 3°, which is the most anomalous shift ever reported. To model such features, we modified Grand's tomography model [Grand et al., GSA Today 7 (1997) 1–7], and generated 2D synthetics to match the data. The overall shape and position of the lower mantle low-velocity anomaly proposed by Grand predicts good results if lower mantle anomalies are enhanced to a level of about 4%. This results in a complex tabular structure extending upward from the core–mantle boundary about 1500 km into the mantle. These features appear to be consistent with a large young plume which is erupting off the CMB.  相似文献   

Spatial and temporal patterns in the hyperbenthic community structure in a warm temperate southern African permanently open estuary     

Elodie Heyns  William Froneman 《Estuarine, Coastal and Shelf Science》2010

The spatial and temporal patterns in the hyperbenthic community structure (>500 μm) in the warm temperate, permanently open Kariega Estuary situated along the south-eastern coastline of South Africa was investigated monthly over a period of twelve months. Data were collected using a modified hyperbenthic sledge at six stations along the length of the estuary. Physico-chemical data indicate the presence of a constant reverse salinity gradient, with highest salinities measured in the upper reaches and lowest at the mouth of the estuary. Strong seasonal patterns in temperature, dissolved oxygen and total chlorophyll-a (chl-a) concentration were evident. Total average hyperbenthic densities ranged between 0.4 and 166 ind.m⁻³ in the lower net and between 0.2 and 225 ind.m⁻³ in the upper net. Hyperbenthic biomass values ranged between 0.02 and 11.9 mg.dry weight.m⁻³ in the lower net and between 0.02 and 17.4 mg.dry weight.m⁻³ in the upper net. Both the lower and upper nets were numerically dominated by decapods (mainly brachyuran crab zoea) with the exception of June and July 2008 when mysids (mainly Mesopodopsis wooldridgei) dominated, comprising up to 72.4 ± 58.14% of the total abundance in the lower net. A redundancy analysis (RDA) indicated that 99.2% of the variance in the hyperbenthic community structure could be explained by the first two canonical axes. Axis one, which accounted for 96.8% of the total variation detected in the ordination plot was highly correlated with sedimentary organic content and to a lesser extent the chl-a concentration within the Kariega Estuary. The correlations with the second canonical axis (2.4%) were less obvious, however, salinity and seston concentration were weakly correlated with this axis.  相似文献   

2018年春季北京一次沙尘天气边界层特征及来源分析     

桂海林  秦贺  赵培涛  王飞  唐志军  王继康  朱媛媛  褚旸晰 《气象与环境学报》2021,37(4):18-25

2018年3月27-28日,内蒙古中东部、中国东北地区、华北等地出现一次大范围沙尘天气。28日凌晨,沙尘进入北京,受此影响北京出现了严重的污染天气。本文利用中国气象局地面常规观测资料、气溶胶激光雷达、风廓线雷达资料、生态环境部大气成分等资料分析了北京沙尘天气前后边界层特征、沙尘来源以及沙尘天气前后大气污染特征。结果表明：此次沙尘天气期间,北京沙尘气溶胶退偏振比约为0.25-0.40,退偏振比数据显示此次沙尘首先从高空进入北京,比地面提前6 h。此次影响北京的沙尘主要来自于北路,东路沙尘有一定补充;沙尘影响时段,北京Ca、Fe、Na、K、Mn等元素浓度显著升高,与该物质地壳丰度相当,污染物元素Cu、Zn、Pb、Cd、As等浓度有所降低,丰度远大于该物质在地壳中丰度。  相似文献   

1961-2020年郑州主城区大气自净能力变化特征分析     

刘美  姬兴杰  田力  丁亚磊  左璇 《气象与环境学报》2022,38(3):93-100

利用郑州市主城区1961—2020年气象观测资料和2014—2018年空气质量监测数据,分析了郑州主城区大气自净能力指数的长期变化趋势与影响因子以及2014—2018年主城区大气自净能力与PM_(2.5)的关系。结果表明:郑州主城区大气自净能力指数30 a气候均值为4.42 t·(d·km^(2))^(-1),春季大气自净能力最强,为5.20 t·(d·km^(2))^(-1);秋季大气自净能力最弱,为3.88 t·(d·km^(2))^(-1),不利于对大气污染物的清除。1961—2020年郑州主城区大气自净能力呈显著的减弱趋势,其中1969年最强为6.85 t·(d·km^(2))^(-1),2020年最弱为3.06 t·(d·km^(2))^(-1)。影响因子中,1961—1980年混合层厚度与大气自净能力指数呈正相关;日平均风速≥2.5 m·s^(-1)的日数和小风日数与大气自净能力分别呈正、负显著相关;大气自净能力指数与降水日数显著相关,2015年后偏强降水日数的增加对大气自净能力在同时期的增强有一定影响。此外,研究还表明主城区大气自净能力和PM_(2.5)浓度存在显著的负相关,说明大气自净能力强时,对应的PM_(2.5)浓度低,环境空气质量趋好。  相似文献   

基于旋翼无人机的大气边界层环境气象垂直观测及订正方法的研究     

徐家平  赵天良  陈燕  白永清  孙晓芸  王淞  曹畅 《气象与环境学报》2022,38(3):101-111

基于旋翼无人机开展大气边界层观测可为气象要素和大气污染物垂直结构的研究提供具有高时空解析能力的新方法,有助于深入理解低层大气物理化学变化机制。本文详述了旋翼无人机在开展大气边界层环境气象垂直观测实验的应用及优势。基于自主研发的旋翼无人机环境气象观测平台,通过开展传感器在无人机上不同的搭载位置,以及旋翼无人机与探空气球、高塔的对比观测实验,明确了旋翼无人机对气象环境观测的影响及合理的搭载方式。研究进一步在湖北重污染天气条件下开展了0—1000 m的大气边界层垂直观测,并研发了基于旋翼无人机姿态数据的大气边界层气象要素及污染物垂直观测的订正方法。结果表明:实验获取了2—10 m垂直分辨率的高质量大气廓线数据,可精细捕捉大气边界层及其逆温层高度和污染物浓度等要素的垂直变化特征。本文旨在为无人机观测的科研应用提供一种技术可行且数据可靠的观测手段。  相似文献   

Observational Subseasonal Variability of the PM_2.5 Concentration in the Beijing-Tianjin-Hebei Area during the January 2021 Sudden Stratospheric Warming     

Qian LU  Jian RAO  Chunhua SHI  Dong GUO  Ji WANG  Zhuoqi LIANG  Tian WANG 《大气科学进展》2022,39(10):1623-1636

It is still not well understood if subseasonal variability of the local PM_2.5 in the Beijing-Tianjin-Hebei (BTH) region is affected by the stratospheric state. Using PM_2.5 observations and the ERA5 reanalysis, the evolution of the air quality in BTH during the January 2021 sudden stratospheric warming (SSW) is explored. The subseasonal variability of the PM_2.5 concentration after the SSW onset is evidently enhanced. Stratospheric circumpolar easterly anomalies lasted for 53 days during the January–February 2021 SSW with two evident stratospheric pulses arriving at the ground. During the tropospheric wave weakening period and the intermittent period of dormant stratospheric pulses, the East Asian winter monsoon weakened, anomalous temperature inversion developed in the lower troposphere, anomalous surface southerlies prevailed, atmospheric moisture increased, and the boundary layer top height lowered, all of which favor the accumulation of pollutant particulates, leading to two periods of pollution processes in the BTH region. In the phase of strengthened East Asian winter monsoon around the very beginning of the SSW and another two periods when stratospheric pulses had reached the near surface, opposite-signed circulation patterns and meteorological conditions were observed, which helped to dilute and diffuse air pollutants in the BTH region. As a result, the air quality was excellent during the two periods when the stratospheric pulse had reached the near surface. The increased subseasonal variation of the regional pollutant particulates after the SSW onset highlights the important role of the stratosphere in the regional environment and provides implications for the environmental prediction.  相似文献   

Role of external forcing on the seasonal and interannual variability of mixed layer depth over the Bay of Bengal using reanalysis datasets during 1980–2015     

《Dynamics of Atmospheres and Oceans》2021

The monsoon reversal winds in different seasons and high influx of freshwater from various rivers make the Bay of Bengal (BoB) a unique region. Thus, the knowledge of the dynamics of the mixed layer over this region is very important to assess the climatic variation of the Indian subcontinent. A comprehensive study of the role of external forcing on the seasonal and interannual mixed layer depth (MLD) variability over the BoB is carried out for 36 years (1980–2015) using reanalysis products. A weak and strong seasonality of MLD is observed over the northern and the southern BoB (NBoB and SBoB) respectively. The partial correlation suggests that the net heat flux (Qnet) is the major contributor to the deepening of MLD over the NBoB, whereas the wind stress controls the deepening over the SBoB. The seasonal variability reveals the deepening of MLD during summer and winter monsoon and the shallowing during pre- and post-monsoon over the BoB. The relation of the interannual MLD variability and the different phases of the Indian Ocean Dipole (IOD) reveals that the negative phase of IOD is associated with deeper MLD over BoB while the positive phase of IOD depicts shallower MLD. In addition, the opposing characteristic of MLD is highly prominent during October-December. This is majorly contributed by variations related to the second downwelling Kelvin and associated Rossby waves over BoB for the opposing phases of the IOD years.  相似文献   

南海台风边界层湍流小波分析          下载免费PDF全文

涂朝勇  赵中阔  黎伟标  陈淑敏  陈逸伦  张奡祺 《热带气象学报》2022,38(4):554-568

利用小波变换（WT）对香港天文台飞机观测台风“妮妲”（1604）资料进行分析,研究在不稳定、不均匀的台风边界层中湍流涡旋的垂直传输作用。在0.1~5 Hz惯性子区内横风和顺风分量功率谱密度能较好符合-5/3幂律。小波分析显示:横风的小波功率谱峰值集中在1 km之下,顺风分量的小波功率谱峰值集中在1~6 km之间;眼区动量通量的主要贡献尺度为2.3 km,眼区外主要贡献尺度在1~2 km,中低层为较小尺度（< 1.0 km）;湍流功能(TKE)的生成尺度主要集中在4 km之下。这项研究定量描述了南海北部台风边界层各个区域湍流结构的差异特征,讨论了对台风边界层通量参数化的可能影响。   相似文献