The effect of varied dam release mechanisms and storage volume on downstream river thermal regimes     

《Limnologica》2020

Temperature plays an essential role in the ecology and biology of aquatic ecosystems. The use of dams to store and subsequently re-regulate river flows can have a negative impact on the natural thermal regime of rivers, causing thermal pollution of downstream river ecosystems. Autonomous thermal loggers were used to measure temperature changes downstream of a large dam on the Macquarie River, in Australia’s Murray-Darling Basin to quantify the effect of release mechanisms and dam storage volume on the downstream thermal regime. The magnitude of thermal pollution in the downstream river was affected by different release mechanisms, including bottom-level outlet releases, a thermal curtain (which draws water from above the hypolimnion), and spill-way release. Dam storage volume was linked to the magnitude of thermal pollution downstream; high storage volumes were related to severe thermal suppressions, with an approximate 10 °C difference occurring when water originated from high and low storage volumes. Downstream temperatures were 8 ̶ 10 °C higher when surface releases were used via a thermal curtain and the spillway to mitigate cold water pollution that frequently occurs in the river. Demonstrating the effectiveness of engineering and operational strategies used to mitigate cold water pollution highlight their potential contribution to fish conservation, threatened species recovery and environmental remediation of aquatic ecosystems.  相似文献   

两次华北冷涡过程雹云结构特征及AgI催化效果数值研究   总被引：5，自引：4，他引：1  

迟竹萍  刘诗军 《气象科学》2005,25(1):61-70

用三维完全弹性非静力平衡雹云模式模拟了不同低涡雹云演变特征和人工引晶催化效果,结果表明:冷涡雹云中不存在大量的过冷雨滴,过冷水几乎是由云滴组成的,雹胚形成以云霰转化为主,由冰相过程形成降水粒子。近地面有薄逆温层云体,云底温度高,云中垂直运动强,云中过冷云水含量增长迅速且丰富。在雹云主要上升气流到达的过冷水含量大值区下方和过冷水大值区中心部位分别一次引进×107/kg碘化银粒子进行大剂量催化试验,碘化银主要以凝结-冻结方式核化成冰,雹胚浓度增加,雹胚过多争食抑制冰雹增长,使得冰雹直径明显减小。  相似文献   

中亚阿拉木图与乌鲁木齐寒潮气候特征对比分析     

段均泽  毛炜峄  张同文  刘精 《沙漠与绿洲气象(新疆气象)》2018,12(4):1-6

利用1951—2016年阿拉木图与乌鲁木齐的逐日气象观测资料,对比分析中亚区域两个主要城市的寒潮气候变化特征。结果表明:(1)阿拉木图和乌鲁木齐的年寒潮过程频数分别为6.1次和4.2次,阿拉木图的寒潮过程较频繁;阿拉木图的寒潮过程年内分布呈单峰型,峰值在11月和12月,而乌鲁木齐的过程频数年内分布呈双峰型,分别出现在4月和11月;阿拉木图的冬半年寒潮过程初日和终日均比乌鲁木齐偏早9 d。(2)1951—2006年,阿拉木图和乌鲁木齐的年寒潮过程频数均呈线性减少趋势,阿拉木图的减少趋势更加显著;阿拉木图与乌鲁木齐的寒潮过程异常偏多年主要出现在1980年之前;阿拉木图的年寒潮过程频数存在21 a显著周期,乌鲁木齐存在39 a显著周期。(3)乌鲁木齐的寒潮过程最低气温低于阿拉木图,但是阿拉木图的寒潮过程降温幅度强于乌鲁木齐;56 a来,阿拉木图和乌鲁木齐的寒潮过程降温幅度的年累计值的变化率分别为-8.1℃/10 a和-5.9℃/10 a,相比而言,阿拉木图的寒潮过程强度的减弱趋势更加显著。  相似文献   

冷空气对夏季高原涡移出高原后长久与短期活动影响的对比分析     

郁淑华  高文良 《大气科学》2018,42(6):1297-1326

本文利用NCEP/NCAR-FNL再分析资料、历史天气图和青藏高原低涡切变线年鉴,通过分析1998~2016年高原涡活动情况,对在高原以东活动时间大于96 h的高原涡（长持续涡）和在高原以东活动时间不大于30 h的高原涡（短持续涡）,进行了环流与冷空气活动特征与位涡诊断的对比分析,得出了长、短持续涡的环境场、冷空气活动特征,揭示了冷空气活动、高空锋区对长、短持续涡的影响。结果表明:（1）长持续涡移出高原后是在受较明显冷空气影响情况下加强并持续的,短持续涡则没有明显受冷空气影响。长持续涡所处的低槽较深,槽后的冷温度槽较明显,副热带高压（简称副高）偏南;短持续涡处在分裂槽中,有冷舌,副高偏北;说明影响低涡活动的天气系统强,槽后的冷温度槽明显,副高偏南是低涡能较长时间持续的重要环流条件。（2）长持续涡不仅受到较强冷平流的影响,还处在有狭长的干冷与暖湿空气相遇的地带,使涡区极易产生对流不稳定和低涡扰动,利于低涡加强并持续,短持续涡则远不及长持续涡。（3）长持续涡移出高原后受两个不同方向冷空气影响,涡区内一般伴有两个高位涡中心区,而短持续涡的只有一个高位涡中心区,且位涡值比长持续涡小,长持续涡活动过程中的斜压性也比短持续涡强。另外,长持续涡活动过程中相应的高空急流较强,在增强、东伸、南压作用下,造成200 hPa高空有高位涡下传到低涡,而短持续涡所伴的西风急流平直、弱,造成了短持续涡只受到400 hPa高位涡下传的影响。（4）冷空气影响高原涡维持的作用有:使影响高原涡活动的天气系统加强;使高原涡斜压性增强、对流不稳定增强;使高空有高位涡下传至低涡附近层次,造成低涡区域正位涡异常,垂直涡度发展,低涡加强。  相似文献   

Influence of benthic sediment transport on cold‐water coral bank morphology and growth: the example of the Darwin Mounds,north‐east Atlantic     

ANDREW J. WHEELER  MAXIM KOZACHENKO  DOUG G. MASSON  VEERLE A. I. HUVENNE 《Sedimentology》2008,55(6):1875-1887

The Darwin Mounds are small (up to 70 m in diameter), discrete cold‐water coral banks found at c. 950 m water depth in the northern Rockall Trough, north‐east Atlantic. Formerly described in terms of their genesis, the Darwin Mounds are re‐evaluated here in terms of mound growth processes based on 100 and 410 kHz side‐scan sonar data. The side‐scan sonar coverage is divided into a series of acoustic facies representing increasing current speed and sediment transport/erosion from south to north: pockmark facies, ‘mounds within depressions’ facies, Darwin Mound facies, stippled seabed facies and sand wave facies. Mound morphometric changes are quantified and show a south‐to‐north divergence from an inherited morphology, reflecting the outline of coral‐colonized fluid escape structures, to developed, downstream elongated, elevated mound forms. It is postulated that increasing current speeds and bedload sand transport favour mound growth and development by a process of enhanced sand sedimentation within mounds due to current deceleration by frictional drag around coral colonies. Comparisons are made with similar growth processes attributed to comparably sized cold‐water coral mounds in the Porcupine Seabight, offshore Ireland.  相似文献   

不同定义指标下的乌鲁木齐寒潮过程气候特征对比分析     

曹兴  毛炜峄 《沙漠与绿洲气象(新疆气象)》2017,11(3):31-37

利用乌鲁木齐市1951—2015年逐日最低气温(TD)、日平均气温(TT)资料,依据《寒潮等级》国家标准,以TD、TT为定义指标来普查寒潮降温过程,采用数理统计方法对2种指标统计的寒潮降温气候变化特征进行对比分析。结果表明:2种指标方法统计的降温频数存在显著性差异,在年际、季节时间尺度上均呈不显著减少趋势,TT法统计的年降温频数减少趋势显著强于TD法;90%的降温过程持续时间在1~3 d,TD、TT法统计的最长降温持续日数均出现在11月,且不同降温幅度的频数最大值亦在秋季;以TD、TT法统计的全年95.5%和94.6%的降温过程达不到寒潮的标准,2种方法统计的寒潮等级频数均表现为一般寒潮强寒潮特强寒潮;2种方法统计的寒潮频数在年际、季节尺度上均呈现减少趋势,峰值期分别为4月和10月,20世纪50年代为多发期,2001—2015年为相对少发期;TT法统计寒潮频数未来持续性强度弱于TD法;相关性分析发现,寒潮频数与年均TD、TT呈极显著的负相关关系,且年均TD的相关性强于年均TT,表明TD是影响寒潮频数变化的一个重要指标参数。  相似文献   

Changes of cloud microphysical properties during the transition from supercooled to mixed-phase conditions during CIME     

Stephan Mertes  Alfons Schwarzenbck  Paolo Laj  Wolfram Wobrock  Jean-Marc Pichon  Giordano Orsi  Jost Heintzenberg 《Atmospheric Research》2001,58(4)

A ground-based seeding experiment using carbon dioxide and propane sprayed from pressurized bottles was carried out under supercooled cloud conditions on a small spatial and short time scale. Water vapor deposition on the artificially generated dry ice and propane ice germs as the main ice formation process (nucleation and growth) is consistent with the experimental results. After nucleation, diffusional growth of the ice particles, partly at the expense of evaporating small droplets, was identified during the mixing of the seeding line with the ambient supercooled cloud. Within the seeding plume, ice water contents up to 80% of the total condensed water are observed, although the size of the formed ice particles did not exceed 25 μm. From the changes of the ice and supercooled liquid phase with time under mixed-phase conditions, liquid water content (LWC) evaporation, ice water content (IWC) formation, and ice crystal growth rates are estimated, which are not affected by the artificial nucleation process. Thus, these rates are assessed to be applicable for a growing ice phase of small ice particles in a young mixed-phase cloud, where other growth mechanisms, like riming or aggregation, are negligible.  相似文献   

用主分量方法分析广东春季低温阴雨年景   总被引：1，自引：0，他引：1  

徐小英  简裕庚 《热带地理》1997,17(4):364-370

本文利用主分量方法对广东47站1954～1991年2～3月平均温度和广东2～3月间低温阴雨出现年景进行统计分析，根据主分量原理，计算该时期温度的时空分布特征，直接评价低温阴雨出现年景：①广东2～3月温度时空分布极为集中，第1主分量已占埸的总方差的95．1％；③用前4个主分量及其对应的特征向量配合划分温度分布类型；③广东2～3月温度分布主要由2个类型控制，即全省一致的偏低（或高）分布和南暖北冷或南冷北暧分布．由主分量极大值（正）和极小值（负）表明：1957、1968、1969年为全省性温度偏低年，1973和1987年为全省性温度偏高年。这些年份恰好对应广东2～3月低温阴雨严重和轻微（或无）的年份。  相似文献   

强天气冷涡云系结构的分析和物理解释     

杨红梅  陶祖钰 《大气科学》1992,16(1):77-83

本文分析了三个产生强对流天气冷涡过程的卫星云图.冷涡云系的结构可归纳为单纯的冷涡结构和具有锢囚气旋结构两类.利用诊断分析对冷涡云系中各个组成部分,即涡旋云区、不稳定云区、正涡度平流云区、冷涡云区及暖锋云区与有关物理量的配置关系进行了讨论.  相似文献   

冬季风爆发前西伯利亚高压的演变   总被引：2，自引：0，他引：2  

谢安  卢莹  陈受钧 《大气科学》1992,16(6):677-685

本文是一次个例的诊断分析,应用FGGE-Ⅲ_b资料分析了1979年11月12—17日的东亚寒潮过程,着重讨论冷空气爆发前,位于两伯利亚的冷堆的增强过程,运用准拉格朗日坐标系的热量方程和涡度方程诊断了500hPa冷中心的温度变化和地面冷高压上空涡度演变的物理过程,分析结果说明,冷堆的增强与高空槽后急流中心前方出口附近的侧向环流有密切关系,开始时500hPa冷中心就位于此侧向环流的上升支附近,绝热冷却是冷堆加强的主要因子,即动力因子是主要的,冷高压上空的涡度变化与相对的涡度平流关系密切,它也与高空急流的相对位置有关,在地面高压加强的后期,散度项和平流项对于温度变化的贡献相反,但它们的垂直分布都有利于下沉运动加剧.因此,在分析预报中要密切注意忽流的动态. 本文的分析结果将有助于进一步理解冷空气增强的物理机制,也为寒潮过程的分析预报提供一定的参考.  相似文献