2000年春季沙尘暴动力学特征

综合分析研究2000年春季影响北京地区沙尘暴天气过程, 揭示了沙尘暴天气在起沙、扬沙、水平输送以及沉降过程中关键动力学问题. 研究结果表明, 2000年3~4月份影响北京地区沙尘暴过程起沙的动力条件与春季冷空气活动等气候因素有关, 并与北方土壤干土层面积、地面风场摩擦速度呈异常显著相关. 沙尘暴活动特征可用起沙-扬沙-远距离输送综合物理模型来描述. 研究结果为我国沙尘暴预报理论和治理决策提供了科学依据.     

三峡水库运用后荆江段非均匀悬沙恢复特性

三峡工程运用后,坝下游荆江段来沙量大幅度减小,处于严重的不平衡输沙状态,次饱和水流冲刷河床使悬沙量沿程恢复.基于实测水沙资料,分析了三峡工程运用后荆江段非均匀悬沙恢复特点.提出了恢复效率的概念用以表征悬移质沿程恢复的程度,并根据实测水沙资料计算了荆江段1994-2017年非均匀悬沙的恢复效率.结果表明：三峡工程运用前,荆江段各粒径组悬沙恢复效率绝对值均接近0,故该时期内各粒径组泥沙冲淤幅度不大;三峡工程运用后,各粒径组悬沙恢复效率绝对值均明显增大,且粗沙（d>0.125 mm）恢复效率绝对值远大于细沙（d<0.125 mm）,故粗沙恢复程度更高.这主要是由于荆江段床沙组成中粗沙部分含量大,而细沙含量小.最后建立了三峡水库蓄水后非均匀悬沙恢复效率与来水来沙条件（来沙系数）的关系,结果表明：各粒径组悬移质恢复效率均与来沙系数呈正相关关系,全沙、细沙和中沙的决定系数（R²）分别为0.89、0.67和0.69,相关性较高,故荆江段各粒径组悬移质泥沙恢复效率较大程度上受到来水来沙条件的影响.     

沙尘暴电效应的实验观测研究

利用国内大型风沙物理风洞实验模拟沙尘暴电现象,研究风沙起电机理,结果表 明,不同风速下不同沙粒会产生不同极性的电场强度和电位效应,风沙电随风速增大而增强 ,且随沙粒度增大而减小. 在沙漠区的16m,8m,4m和1m高度上观测到27次不同沙尘暴天气 过程的电场和风速随时间变化. 结果表明, 在晴天4个高度上的电场均为小正电场值,电场 随高度降低而减小,最大电场强度在5kV/m以下,日风速变化对各层电场起伏没有较大影响 . 有沙尘天气,各高度上的电场强度随风速变化而变化. 16m高度上电场均为负值,平均值 为 -20kV/m;中层8m 电场一般为较高正电场值,达到10～40kV/m,与16m高度上电场呈反相 关;下层1m 电场值变化一般很小,在1kV/m以下. 在强沙尘暴天气4个高度上的电场均为负 电值,电场值随高度降低而减小,16m高度上最大平均电场强度达到-200kV/m以上,瞬时值 超过 -2500kV/m,与晴天电场矢量相反.     

长江中游沙质河段床沙级配调整过程计算

三峡工程运用后,长江中游荆江河段持续冲刷,床沙与推移质、悬移质泥沙不断交换,从而造成该河段床沙发生不同程度的调整,对长江中下游河床演变及非平衡输沙机理的研究具有重要影响.在新水沙条件下,总结分析了沙波运动特性及床沙交换方式,引入Markov三态转移概率及非均匀沙隐暴系数,得到基于状态转移概率的沙质河段床沙级配调整的计算模型.研究结果表明:(1)20092014年,沙市站年内床沙中值粒径有先增大后减小的趋势,而监利站年内床沙中值粒径则先减小后增大,且荆江河段年际床沙中值粒径总体呈上升趋势,粗化程度约为6.9%~9.3%;(2)20092014年,沙市站床沙组成中粒径d<0.062 mm的泥沙所占比重不变,0.062 mm≤d<0.25 mm的泥沙所占比重逐年减少(累计减少11.4%),d≥0.25 mm的泥沙所占比重逐年增加(累计增加11.4%),而监利站床沙组成均存在波动性变化;(3)荆江河段床沙转换为推移质的概率随着泥沙粒径的增大而增大,床沙转换为悬移质的概率随着泥沙粒径的增大而减小,而推移质和悬移质转换为床沙的概率均随着泥沙粒径的增大而增大,河床发生冲刷粗化时泥沙输移的主要形式为悬移质(概率为81%~87%),而淤积细化时床沙补给主要来源于推移质(概率为8%~12%).通过验证,本文概率模型的计算结果与实测资料符合较好,能够应用于长江中游沙质河段年际床沙粗化及年内床沙级配调整过程预报,为进一步开展三峡工程下游非均匀悬移质泥沙沿程恢复机理的研究提供理论基础.     

印度洋偶极子对北印度洋热带气旋活动的影响研究

利用JTWC提供的1981～2010年北印度洋热带气旋路径资料,NECP提供的风场、OLR场等资料,以及NOAA提供的SST资料,使用统计诊断方法研究了北印度洋热带气旋活动时空分布特征及其与印度洋海温的关系.结果表明：北印度洋热带气旋活动频次EOF1占总方差贡献的比例为16%,反映了北印度洋整个海盆尺度热带气旋活动频次变化基本一致的分布形态,但是其空间分布具有不均匀性,表现为以孟加拉湾热带气旋偏西路径变化为主的特征;小波分析表明EOF1模态有显著的准5年变化周期.印度洋偶极子对北印度洋热带气旋活动年际变化影响显著,其影响机制概念模型为：印度洋偶极子处于正（负）位相模态时,印度洋海温异常呈显著的西暖东冷（西冷东暖）型分布,造成北印度洋上空对流减弱（加强）、低层有反气旋（气旋）式环流异常,不利（有利）于热带气旋在北印度洋生成,北印度洋热带气旋活动频次偏少（多）;且可造成孟加拉湾上空西风引导气流加强（减弱）,进一步使得出现在孟加拉湾90°E以西的偏西路径热带气旋偏少（多）.     

气溶胶对雷暴云电过程影响的数值模拟研究

本文在已有的三维雷暴云起、放电模式中加入了一种经典的气溶胶活化参数化方案,结合一次长春雷暴个例,进行了雷暴云起放电数值模拟试验.研究显示气溶胶浓度改变对雷暴云微物理、起电及放电过程都有重要影响.结果表明:(1)污染型雷暴云中气溶胶浓度增加时,云滴数目增多,上升风速加强;云中冰晶与霰粒子数浓度增加但尺度减小;(2)相对于清洁型雷暴云,污染型雷暴云非感应起电过程弱,感应起电过程强,起电持续时间长;(3)污染型雷暴云中首次放电时间延迟,闪电持续发生的时间长,总闪电频次增加,正地闪频次增加明显.     

2.7～1.6ka BP塔克拉玛干沙漠腹地克里雅河尾闾绿洲的变迁

沿塔克拉玛干沙漠腹地克里雅河现代绿洲尾闾达理雅博依以西的古河道,对圆沙古城遗址（38°52′N,81°35′E）所在的干三角洲进行了实地考察,发现陶石器残片、砍剁木及铜器小件等古人类活动遗迹点百余处,采集到能够反映古人类活动及自然环境变迁的14C年龄样品14个及沉积物光释光（OSL）年龄样品5个并进行了测定,结果表明：圆沙古城及其周围的绿洲至少约2.6kaBP于春秋时代（公元前716～475年）就已存在;约2.2kaBP,流经古城遗址的古河道曾发生断流,绿洲主体随克里雅河东迁至喀拉墩一带,成为史载西汉时期（公元前206～公元25年）塔里木丝路南道古国扜弥重要领地;约1.9kaBP,克里雅河曾再次在圆沙古城一带发育绿洲,该绿洲属东汉（公元24～220年）扜弥国,约至1.6kaBP与精绝和楼兰等塔里木盆地古绿洲同期废弃.圆沙等古绿洲的发育演变暗示,塔里木盆地铁器时代文明的开始可能与我国西部的2.8kaBP冰进事件有关,而其约1.6kaBP的消亡则与塔里木盆地精绝和楼兰等古绿洲的衰退可能有相似的原因.应用地貌学和考古学对圆沙干三角洲的年代学分析,为汉代及之前塔里木盆地的绿洲演化与环境变迁研究提供了证据.     

2013年1月中国东部持续性强雾霾天气产生的气象条件分析

2013年1月,在中国东部地区发生了强度强、持续时间长、发生范围广的雾霾天气．本文利用资料诊断,从大气环流背景场和雾霾天气演变过程两个方面,分析了气象条件在这次持续性强雾霾天气发生中的作用．结果表明,2013年1月东亚冬季风异常偏弱,在中国东部区域,对流层中低层的异常南风有利于水汽向中国东部地区输送,500hPa的高压异常抑制了对流的发展,而表面风速的减弱不利于近地面附近的雾霾向区域外输送,水平风垂直梯度的减小减弱了天气尺度扰动的发展和大气的垂直混合,对流层低层异常逆温层的存在使得大气近地层变得更加稳定．这些气象背景场为雾霾天气的维持和发展提供了有利的气象条件．对雾霾天气演变过程的分析表明,雾霾天气区域内的表面风速及其上空对流层中低层的水平风垂直切变对雾霾天气过程具有动力影响,二者偏小（大）时雾霾天气偏强（弱）;对流层中低层的层结不稳定性以及近地面层的逆温状况和温度露点差对雾霾天气的演变可以产生热力影响,层结不稳定性和逆温偏大（小）以及温度露点差偏小（大）时雾霾天气偏强（弱）．多元线性回归分析的结果表明,热力和动力因子对这次雾霾天气过程具有大致相同的作用,气象因子可以解释超过2／3的雾霾天气逐日变化的方差,方差贡献达到0．68．     

2008年和2012年冬季欧洲气候的差异及成因

2008年冬季（1月和2月）和2012年冬季均发生了较强的拉尼娜事件,但欧洲气候,尤其是西欧在这两年差异较大,2008年异常偏暖,而2012年却出现了极寒事件.诊断表明,大气环流异常是造成气候差异的直接原因.2008年冬季,北大西洋上空大气环流异常呈正位相的北大西洋涛动,有利于欧洲异常偏暖;2012年冬季,北大西洋和欧亚高纬阻塞的长期维持是西欧发生极端严寒的重要原因.通过数值试验,研究了前期海表热状况异常对大气的影响.结果表明：北大西洋海温异常能在一定程度上解释这两年欧洲各自的气候异常;尽管热带海温异常对2012年冬季的北大西洋环流形势和欧洲气候异常起一定的贡献,但不能解释2008年的情形;靠近欧洲的北极海冰异常偏少使得欧洲气候偏冷,对2008年的偏暖气候贡献为负,对2012年则有正贡献.     

东亚一次典型切断低压引起的平流层空气深入侵过程的分析

利用ERA-Interim再分析资料、卫星资料以及轨迹模式,对2010年6月19-23日东亚夏季一次典型切断低压（COL）过程中的动力、热力及化学结构进行了分析,并详细分析了平流层空气深入侵过程和路径.AIRS臭氧资料与臭氧探空资料分析表明,在COL发展成熟阶段,由极区高位势涡度、高臭氧库区脱离出来的空气在COL的中心形成一个局地高位势涡度与高臭氧浓度区域,并在对流层中上部出现臭氧次峰结构.前向轨迹模式模拟结果表明：COL形成前期,高空槽加深,槽后偏北风急流可以引起极区下平流层空气向中纬度对流层中低层侵入,从而使对流层中低层臭氧浓度升高;COL发展成熟阶段,可以引起平流层空气的＂旋转式＂入侵.最后,应用后向轨迹模式对成熟阶段COL内部及周围空气块源地做进一步模拟分析.结果表明：（1）COL中心高浓度臭氧空气块源地有两个,一是中西伯利亚北部上空的副极地涡旋,这部分气块对COL中心的高臭氧浓度起主要作用;二是90°E以西,50°N附近的温带急流轴左侧的气旋式风速切变区.（2）COL周围低臭氧浓度的气块源地也有两个,一是COL底部臭氧浓度相对较低的空气块主要来自急流轴右侧反气旋式风速切变区,以平流运动为主;二是COL前部及后部的空气块主要来自COL南侧低层暖区,以上升运动为主.     

The long-term simulation of surface SO2 and evaluation of contributions from the different emission sources to Beijing city

With a high-resolution SO2 emission inventory categorized by industries and seasons for Beijing city and gridded meteorological data fields from NCEP, the pollution dispersion model, HYSPLIT4 (Hybrid Single Particulate Lagrangian Integrated Trajectory, version 4), is used to determine the day-to-day variation of surface SO2 in Beijing for 2000 and 2001. Furthermore,the contributions of different emission sources in and around Beijing to the surface SO2 are studied. As shown in comparison with observations, the model does well in simulating the daily variation and seasonal distribution. The model computation of the annual source contributions to Beijing surface SO2 indicates that local emissions from the city give the largest contribution and the sources from the surrounding regions contribute only about 20%. During SO2 polluted or unpolluted days, the contribution from the latter can exceed 30%, and depending upon weather conditions, the contribution may exceed 40%. If the emissions from the surrounding sources during the winter heating season are assumed to be doubled in intensity, their contribution to surface SO2 in Beijing increased from 21% to 35% and 25% to 40% in 2000 and 2001, respectively. Evaluation of 7 types of emission sources identified for Beijing for their relative contribution to the concentration of surface SO2 has shown that area emissions by industrial production and furnaces, though discharging relatively small amounts (less than 1/3 of the total), have the largest contribution to the urban surface SO2, which is the key to the mitigation of the pollutant in the city.     

Das diffuse Himmelslicht in der hohen Atmosphäre

Summary Devices developped in our laboratory for measurement of the diffuse sky light were shot with the French rocket Véronique into the sky over the Sahara. The measurements are discussed in detail. The final result is given in Fig. 6 with a plot of the diffuse sky light of a unit air mass as a function of altitude. At first the emission decreases to a minimum value in the tropopause due to the Rayleigh scattering of air molecules. Then the values increase to a maximum at an altitude of 25 km that is attributed to solid particles existing in a zone over the tropopause. The periods for rotation and precession of the rocket could be determined owing to the sun looking into the device.     

Numerical modelling of spectral sky radiance during a total solar eclipse

Ground-based observations of the spectral sky radiance within the totality region during a total solar eclipse are of significant interest because the contribution from direct and single scattered light from the solar disk is eliminated. In the present paper, we develop a numerical model of the spectral sky radiance during totality, evaluate the contribution of double scattered sunlight to the sky radiance at totality and compare it to solar corona emissions. The results show that the single scattered coronal light is the major contaminant in ground-based observations of the corona, opposite to what was believed before. For observation directions outside the corona the double scattered sun radiation dominates over the single scattered coronal light.     

煤样变形破坏声电效应的演化规律及机理研究

通过实验研究不同煤样变形破坏全过程的声发射和电磁辐射效应的演化规律，分析了煤样变形破坏过程中电磁辐射和声发射信号的相关性和煤样变形破坏的微观机理，提出了煤样变形破坏过程中电磁辐射和声发射信号分别是在煤样内的裂纹面滑移和裂纹扩展时产生的观点，较好地解释了煤样变形破坏过程中声电效应的变化规律和特征，为进一步提高电磁辐射及声发射、电磁辐射综合预测煤岩动力灾害的可靠性和准确性提供了理论基础.     

Spatial–temporal variations of methane emissions from the Ertan hydroelectric reservoir in southwest China

Methane emissions from hydroelectric reservoirs can comprise a considerable portion of anthropogenic methane. However, lack of data on CH₄ emissions in different geographical regions and high spatial‐temporal variability in the emission rates of reservoirs has led to uncertainties regarding regional emission estimates of CH₄. In the subtropical plateau climate region, we used the Ertan hydroelectric reservoir as a study area. The CH₄ flux at the air‐water interface was assessed by floating chambers and factors influencing emissions, including the distance from the dam, water depth, seasonal variation in wet and dry season, air‐water temperature gradient and wind speed, and was also studied through a year‐long systematic sampling and monitoring experiment. The results showed that the surface of the reservoir was a source of CH₄ during the sampling period and the annual average CH₄ flux was 2·80 ± 1·52 mg m^?2 d^?1. CH₄ flux (and its variation) was higher in the shallow water areas than in the deep‐water areas. CH₄ flux near the dam was significantly higher than that of other locations farther from the dam in the dry season. The seasonal variations of CH₄ emission in wet and dry seasons were minor and significant diurnal variations were observed in wet and dry seasons. Exponential relationships between the CH₄ flux and air‐water temperature gradient were found. Air‐water temperature gradient was an important factor influencing diurnal variations of CH₄ flux in the Ertan hydroelectric reservoir. These results indicate that systematic sampling is needed to better estimate CH₄ flux through coverage of the spatial variation of different water depths, measuring‐point distance from the dam, seasonal variation in wet and dry seasons and changes in climate factors (such as air‐water temperature gradient). Our results also provide a fundamental parameter for CH₄ emission estimation of global reservoirs. Copyright © 2010 John Wiley & Sons, Ltd.     

震后恢复重建民用建筑考虑碳排放的研究与监测

为了解决现有震后重建民用建筑碳排放监测方法未考虑节能减排条件与计算碳排放系数，导致监测结果不准确与监测效率低的问题，提出了一种新的震后恢复重建民用建筑考虑碳排放的研究与监测方法。首先针对碳排放研究的基础进行详细阐述，根据国际碳排放标准开展研究；其次采用排放系数方法，完成建筑碳排放数据采集。具体以建筑使用阶段碳排放的边界条件为基础，确定碳排放边界条件，对震后重建民用建筑全生命周期碳排放进行计算，完成震后建筑碳排放量的实时监测。结果表明：提出的震后建筑碳排放量实时监测方法，能有效的对震后建筑的碳排放量进行实时监测，且具有较高的监测效率。     

Optimal reduction of anthropogenic emissions for air pollution control and the retrieval of emission source from observed pollutants Ⅰ. Application of incomplete adjoint operator

The ultimate solution to anthropogenic air pollution depends on an adjustment and upgrade of industrial and energy structures. Before this process can be completed, reducing the anthropogenic pollutant emissions is an effective measure. This is a problem belonging to “Natural Cybernetics”, i.e., the problem of air pollution control should be solved together with the weather prediction; however, this is very complicated. Considering that heavy air pollution usually occurs in stable weather conditions and that the feedbacks between air pollutants and meteorological changes are insufficient, we propose a simplified natural cybernetics method. Here, an off-line air pollution evolution equation is first solved with data from a given anthropogenic emission inventory under the predicted weather conditions, and then, a related “incomplete adjoint problem” is solved to obtain the optimal reduction of anthropogenic emissions. Usually, such solution is sufficient for satisfying the air quality and economical/ social requirements. However, a better solution can be obtained by iteration after updating the emission inventory with the reduced anthropogenic emissions. Then, this paper discusses the retrieval of the pollutant emission source with a known spatio-temporal distribution of the pollutant concentrations, and a feasible mathematical method to achieve this is proposed. The retrieval of emission source would also help control air pollution.     

雁列断层变形过程中的声发射特征

对拉张型、挤压型雁列断层变形过程中岩桥区和主断层上的声发射特征进行了对比研究，结果表明，雁列断层变形中的声发射对应着多种机制：拉张型雁列岩桥区的声发射为单一事件组成，波振幅小、持续时间短、主频高、震源机制为张裂型；挤压型雁列岩桥区的声发射也是单一事件，波振幅较大、持续时间短、主频较低、震源机制为双剪型；而雁列主干断层上的声发射由多事件组成，波振幅大、持续时间长、主频低、震源机制与挤压型雁列岩桥区的声发射机制不同。这些特点与各区域所处力学状态有关     

An analysis of the characteristics of rough bed turbulent shear stresses in an open channel

Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.     

Turbulent flow structures and geomorphic characteristics of a mining affected alluvial channel

Sediment mining in rivers may have a major impact on river geomorphology and research is required to quantify these impacts. In this research, experimental studies were conducted to analyse the morphological changes of channel bed and the turbulent characteristics of flow in the presence of mining. The channel bed profile shows erosion at the bank of the pit and that the erosion expands to the whole width of the channel and propagates downstream with time. The deposition of sediment occurs along the upstream edge of the pit and the depth of the pit decreases with time. Velocity reversal occurs at the central bottom of the pit related to a recirculation zone. Reynolds shear stress and the turbulent intensities become higher in the mining pit region and downstream of it as compared to the upstream section, causing a more rapid movement of bed particles. Analysis of the bursting phenomenon shows that the contribution of sweep and ejection events to the total Reynolds shear stress is more dominant over outward and inward interaction events. The dominance of the sweep event over ejection is observed at the near‐bed region for all the sections, but the depth range of dominance of sweep events in the pit and downstream of the pit is found to be more than the upstream. The increase in thickness is responsible for the increase in bed material transport. The increased sediment transport capacity at the mining pit and downstream of it caused the deformation and lowering of channel bed downstream. An empirical formulation of bedload transport for mining induced channels is derived from two different sized uniform bed materials. Copyright © 2018 John Wiley & Sons, Ltd.