Validation of a regional Indonesian Seas model based on a comparison between model and INSTANT transports

The International Nusantara Stratification and Transport (INSTANT) program measured currents through multiple Indonesian Seas passages simultaneously over a three-year period (from January 2004 to December 2006). The Indonesian Seas region has presented numerous challenges for numerical modelers — the Indonesian Throughflow (ITF) must pass over shallow sills, into deep basins, and through narrow constrictions on its way from the Pacific to the Indian Ocean. As an important region in the global climate puzzle, a number of models have been used to try and best simulate this throughflow. In an attempt to validate our model, we present a comparison between the transports calculated from our model and those calculated from the INSTANT in situ measurements at five passages within the Indonesian Seas (Labani Channel, Lifamatola Passage, Lombok Strait, Ombai Strait, and Timor Passage). Our Princeton Ocean Model (POM) based regional Indonesian Seas model was originally developed to analyze the influence of bottom topography on the temperature and salinity distributions in the Indonesian seas region, to disclose the path of the South Pacific Water from the continuation of the New Guinea Coastal Current entering the region of interest up to the Lifamatola Passage, and to assess the role of the pressure head in driving the ITF and in determining its total transport. Previous studies found that this model reasonably represents the general long-term flow (seasons) through this region. The INSTANT transports were compared to the results of this regional model over multiple timescales. Overall trends are somewhat represented but changes on timescales shorter than seasonal (three months) and longer than annual were not considered in our model. Normal velocities through each passage during every season are plotted. Daily volume transports and transport-weighted temperature and salinity are plotted and seasonal averages are tabulated.     

FY2卫星云图分析系统在热带气旋北冕过程中的应用

利用FY2卫星云图分析系统的各项分析功能,结合常规观测资料对热带气旋北冕的天气形势、云图演变以及路径变化、风雨情况等进行了分析。结果表明,副热带高压摆动,中纬度西风小槽东移,低层西南气流加强和减弱是"北冕"出现两次北抬和一次南折的直接原因;对流云团的发展和减弱对应低层西南气流的加强和减弱;强降水与云顶亮温的最低值中心及强度密切相关,而云团面积和云顶亮温与强降水也有很好的对应关系,其中发展的云系是强降水发生的信号。FY2卫星云图分析系统较好地分析了"北冕"整个过程的变化特点,对于短时临近预报有较好的辅助作用。     

Model analysis of seasonal variations in tropospheric ozone and carbon monoxide over East Asia

Temporal-spatial variations in tropospheric ozone concentrations over East Asia in the period from 1 January 2000 to 31 December 2004 were simulated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS). The simulated concentrations of ozone and carbon monoxide were compared with ground level observations at two remote sites, Ryori (39.03°N, 141.82°E) and Yonagunijima (24.47°N, 123.02°E). The co...     

On the relationship between flow and suspended sediment transport over the crest of a sand dune, Río Paraná, Argentina

The links between large‐scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades, with past studies illustrating the origin of such turbulence and its influence on flow resistance, sediment transport and bedform morphology. In this study of turbulence and sediment suspension over large sand dunes in the Río Paraná, Argentina, time series of three‐dimensional velocity, and at‐a‐point suspended sediment concentration and particle‐size, were measured with an acoustic Doppler current profiler and laser in situ scattering transmissometer, respectively. These time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment. The analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest, where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections. Regions of high suspended sediment concentration are found to correlate well with such events. The frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations. Such a finding suggests that a combination and interaction of vortex shedding and wake flapping/changing length of the lee‐side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes. Wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures, including information on the topology of dune‐related turbulent flow structures. At the flow stage investigated, the turbulent flow events, and their associated high suspended sediment concentrations, are seen to grow with height above the bed until a threshold height (ca 0·45 flow depth) is reached, above which they begin to decay and dissipate.     

水电开发对河流水沙年内分配的影响分析

以中国西南重要的国际河流澜沧江为研究对象,借鉴"基尼系数"的构建思路,建立了水沙年内分配均匀度计算模型,并通过下游水沙与上游天然水沙和区域降水的关系,建立了河流水沙年内分配均匀度回归还原模型。还原结果与实测对比表明:漫湾、大朝山电站建设以来,澜沧江径流年内分配均匀度年均升高1.14%,变幅在-7.32%~10.81%之间,输沙年内分配均匀度年均降低0.23%,变幅在-18.98%~26.76%之间;漫湾、大朝山电站同时运行期间,澜沧江径流年内分配均匀度年均升高3.90%,输沙年内分配均匀度年均降低0.42%;大朝山水电站建设后,澜沧江径流年内分配均匀度升高而输沙年内分配变化不明显,说明大朝山水电建设后河流水沙关系发生了变化,但变化较小。该成果不仅能为相关研究提供方法借鉴,也为水电开发对澜沧江水沙年内分配影响程度的科学评估提供了新的依据。     

杀虫剂在地下环境中的存在与分布

杀虫剂在环境中的存在与分布取决于其类型、施用量、次数、时间、方法以及一系列天然和人为因素,包括水文、地貌、土壤、地表植被、水文地质和气象等条件。文中使用模拟技术定量研究杀虫剂在地下环境中的存在和分布规律;运用一个综合的杀虫剂运移模型(IPTM-CS)模拟了五种不同杀虫剂在耦合植被-土壤系统中的运移过程;通过考察四个不同的方案,综合评价了这些杀虫剂的特性及使用情况对它们在地下系统中存在和分布的影响。研究表明:杀虫剂的形成模式非常复杂,而且时空分布变异性强;尽管杀虫剂的持久性和移动性主要取决于它们本身内在的特性,但杀虫剂的使用情况,包括施用时间、地点和方法确实会对它们在地下环境中的运移途径、迁移过程、机理以及存在和分布产生深刻的影响。     

涡分辨率全球海洋环流模式LICOM模拟的吕宋海峡流场的季节变化

分析了一个1/10°的涡分辨率全球环流模式LICOM(LASG/IAP Climate system Ocean Model)对吕宋海峡附近海洋环流的模拟能力。结果表明,模拟的吕宋海峡附近上层环流及输运具有明显的季节变化特征,除6月是东向净流出外,其余月份均为西向流入,冬季流量最大。年平均流量在-3.76 Sv(1 Sv=106 m3/s),其中上层(600 m以上)流量起主要贡献,为-3.60 Sv,与目前已有的研究结果基本一致。南海通过6个海峡完成与外界的水交换,其中吕宋海峡和巴拉巴克海峡是大洋水进入南海的主要通道,其余海峡均以流出为主,流出量最大的是台湾海峡(1.99 Sv),其次是卡里玛塔海峡(1.03 Sv)。进一步分析表明,由季风引起的埃克曼输送量约占吕宋海峡流量的11%,而由季风引起的吕宋海峡压力梯度形成的西向的地转流对吕宋海峡的输运起支配作用。作为黑潮源头的太平洋北赤道流流量对吕宋海峡输运的季节变化也有一定影响。     

On Outflow Passages in the South China Sea

Both box and inverse methods are used to study the relative importance of outflow passages of the South China Sea.The physical meaning of the box model is described in detail,and its optimization is based on the most efficient way to remove the warm and fresh water in terms of the heat and salt budgets.The box model results suggest that the Kalimantan Strait is the main outflow passage,because the water near the Kalimantan is the warmest and freshest.The system of the South China Sea advects the warmest and...     

热带深对流云对CO、NO、NOx和O3的垂直输送作用

利用2005年11月至2006年2月ACTIVE (Aerosol and Chemical Transport in tropIcal conVEction) 外场试验期间在澳大利亚北部达尔文地区取得的CO、O3、NO和NOx飞机探测资料, 并结合HYSPLIT后向轨迹模式结果, 分析这几种气体成分在对流卷云砧内外的分布情况, 并探讨热带深对流云对于污染气体的垂直输送作用。分析结果显示, 在孤立对流云卷云砧中, 云砧内部O3、NO、NOx浓度均大于云外; 而CO则不同, 只有在近地面浓度高时才如此, 在近地面浓度较小时, 卷云砧内部的浓度反而小于云外。进一步分析造成这两类气体分布差异的原因, 发现CO主要借助深对流云将对流层下层以及对流云周围环境中的CO夹卷并动力垂直输送到对流云顶部卷云砧中, 而对于O3、NO和NOx来说, 除了上述作用以外, 还可能与对流云内部其他物理机制(如闪电), 造成新的O3、NO和NOx有关, 这些新生气体随着风暴内部强烈的上升气流被最终输送进云砧中。     

High frequency stream bed mobility of a low‐gradient agricultural stream with implications on the hyporheic zone

Little Kickapoo Creek (LKC), a low‐gradient stream, mobilizes its streambed–fundamentally altering its near‐surface hyporheic zone–more frequently than do higher‐gradient mountain and karst streams. LKC streambed mobility was assessed through streambed surveys, sediment sampling, and theoretical calculations comparing basal shear stress (τ_b) with critical shear stress (τ_c). Baseflow τ_b is capable of entraining a d₅₀ particle; bankfull flow could entrain a 51·2 mm particle. No particle that large occurs in the top 30 cm of the substrate, suggesting that the top 30 cm of the substrate is mobilized and redistributed during bankfull events. Bankfull events occur on average every 7·6 months; flows capable of entraining d₅₀ and d₈₅ particles occur on average every 0·85 and 2·1 months, respectively. Streambed surveys verify streambed mobility at conditions below bankfull. While higher gradient streams have higher potential energy than LKC, they achieve streambed‐mobilization thresholds less frequently. Heterogeneous sediment redistribution creates an environment where substrate hydraulic conductivity (K) varies over four orders of magnitude. The frequency and magnitude of the substrate entrainment has implications on hyporheic zone function in fluid, solute and thermal transport models, interpretations of hyporheic zone stability, and understanding of LKC's aquatic ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.