塔克拉玛干沙漠腹地一次风蚀起沙观测试验

风蚀起沙对生态环境、人类健康及社会经济等具有很大的负面效应。利用美国Sensit公司生产的H11-LIN型风蚀传感器及贴地层风速梯度探测仪,对塔克拉玛干沙漠腹地塔中地区一次风蚀起沙过程进行了监测。结果表明：（1）风蚀起沙与微气象是一个互相影响互相制约的变化过程;（2）在此次观测试验过程中,我们观测到的最小起沙风速为6.0 m/s左右,同时发现起沙风速是一个变化的值,随着时间的延续呈现逐步增大的趋势,最小的起沙风速出现在风蚀开始发生的时候;（3）近地表风速廓线受沙粒运动影响明显,随着起沙量的增加,风速随高度变化的幅度增大,此时的风速廓线已不再遵循对数分布规律;（4）利用风蚀传感器测得塔中地区沙粒的临界起动摩擦速度为0.25 m/s,该值与经验公式估算的0.24 m/s非常接近,表明风蚀传感器在塔中地区具有较好的适用性;夏季塔中地区地表土壤湿度对风蚀起沙的阻碍作用可以忽略不计。 ?     

敦煌戈壁地表风蚀起沙量的计算

利用三种不同的计算方案,根据敦煌地区的观测资料,计算了2002年4月8日沙尘天气过程中戈壁地表的风蚀起沙量(垂直尘粒通量)。结果表明:三种方法的计算结果比较接近;在风蚀起沙较严重的时段内,顺风向沙粒通量和垂直尘粒通量平均值的量级分别为10-4kg·m-1·s-1和10-8kg·m-2·s-1。通过计算结果和观测结果的比较,在地面风蚀起沙物理机制的基础上,讨论了三种计算方案各自的优缺点。     

中国风蚀起沙研究进展

风蚀起沙是开展沙尘气溶胶和沙尘天气研究的基本问题.从风蚀起沙的机制、粒子运动形态、起沙条件、沙尘通量等几个方面,回顾了我国在风蚀起沙方面的主要研究结果,对开展这方面研究的难点问题开展讨论.介绍了计算临界摩擦速度的不同方法,并对不同研究者在不同地点观测到的临界摩擦速度进行比较.针对提高观测精度和观测研究结果的可比较性问题,提出了三点建议:一是要建立比较详细的地理、地貌和土壤信息系统;二是要利用卫星观测的优势,建立地面对比观测系统,标校卫星遥感结果;三是要规范观测方法和流程,充分利用业务化的观测资料,提高观测的可对比性.     

沙尘天气过程起沙特征的观测试验和参数化研究进展

沙尘天气过程研究中,起沙过程是沙尘传输和沉降的基础,沙尘模式中的起沙参数化方案决定了能否准确模拟和预报沙尘天气。试验观测和数值模拟是研究起沙过程的重要途径。基于风蚀起沙的物理机制,总结了起沙机制和起沙特征的研究成果,介绍了风蚀起沙的主要影响因子,回顾了起沙关键参数（临界起沙摩擦速度（u*t ）或临界起沙风速（Ut ）、水平跃移沙尘通量（Q）和起沙通量（F））的试验观测及其沙尘模式应用中的参数化方案,并讨论了不同起沙参数化方案的应用与校验。同时,针对目前研究中存在的问题和今后可能的研究方向提出建议。     

“近地层沙尘通量观测方法应用推广”项目

<正>一、项目背景沙尘暴数值预报模式风蚀资料库中的起沙关键参数准确率直接影响到模式预报结果。因此准确计算地表风蚀起沙关键参数(粒度、临界起沙摩擦速度、土壤水分条件、输沙量、地表粗糙度等)显得极为重要。目前常规气象观测设备无法得出地表风蚀起沙的关键参数。风洞试验虽然具备可控性,但是无法模拟野外自     

风蚀起沙的影响因子及其变化特征

以敦煌地区的戈壁和绿洲为例,对地表土壤风蚀起沙的临界摩擦速度及其变化特征和风蚀起沙过程中地表土壤的粒子尺度分布及其对垂直尘粒通量的影响进行了分析研究。结果表明,地表土壤风蚀起沙的临界摩擦速度随土壤水分含量和植被覆盖度的增大而增大,随粒子尺度的变化是先减小后增大,在中间某一尺度处有一最小值;土壤的人工利用和管理对临界摩擦速度也有着相当大的影响,风蚀起沙过程中,地表土壤的粒子尺度分布随时间发生变化,瞬时的粒子尺度分布不同于平均的粒子尺度分布,利用前者计算得到的垂直尘粒通量对摩擦速度的变化更敏感,利用后者计算得到的垂直尘粒通量偏大。     

塔克拉玛干沙漠腹地近地表输沙方向探测研究

利用塔克拉玛干沙漠腹地2008年3月—2018年2月实时探测的近地表沙粒运动数据,结合同步观测的气象和土壤等环境数据,分析了该地区近地表输沙方向特征,并基于输沙方向的观测事实,评估了几起沙风风向和输沙势为指标判定输沙方向方法的不确定性。结果表明:(1)塔克拉玛干沙漠腹地近10 a间累计发生风沙活动3 609.8 h,约占总观测时长的4.1%,春、夏、秋、冬起沙时长分别占总起沙时长的39.2%、45.1%、11.8%和3.8%;(2)起沙时风向主要为N-ESE 6组风向,占总起沙时长的68.8%;(3)利用起沙风风向确定的各方向起沙时长百分比分布与实测结果基本一致,二者相关系数r为0.94,各方向的输沙势百分比与起沙颗粒数二者的相关性较好,相关系数r为0.84～0.93。上述研究结果表明起沙风风向适合判定各方向起沙时长百分比;如果考虑起沙风风速变化,输沙势与各方向的输沙量百分比则更加一致。     

中国西北三类典型裸土下垫面地表宽波段发射率变化特征研究

利用2013年我国西北戈壁、沙漠和黄土塬区三类典型裸土下垫面野外观测试验资料,探究了上述地区地表向下、向上长波辐射（DLR&ULR）、地表温度（LST）和地表宽波段发射率（LSBE）的变化特征,结果表明:黄土站地表ULR和LST明显比戈壁和沙漠站偏低;戈壁宽波段发射率（GbBE）、沙漠宽波段发射率（DeBE）和黄土宽波段发射率（LoBE）具有明显的变化特征,尤其是日变化特征;观测期内GbBE、DeBE和LoBE平均值分别约为0.926±0.0452、0.916±0.0419和0.881±0.049。三站点地表宽波段发射率的数值大小和变化特征与陆面模式中所指定的参数化情况不符。地表发射率会受站点周围环境和当时气象条件等因素的影响,表层土壤湿度被认为是一个非常重要的影响因子,将来的野外观测试验中需加强相关影响要素的观测与分析。     

1996—2008年塔中地区的风沙环境特征

对塔中气象站1996—2008年气象数据分析和野外观测试验及理论计算,结果表明:塔中地区地表沙源平均粒径约为2.88φ(136μm),属于细砂、极细砂;年平均风速均在2.5 m·s-1以下,近10年来整体呈下降趋势,风速的年变化呈单峰分布,最大值出现在6—7月,风向与起沙风向以偏东风为主;2 m高度的起沙风速约为4.1 m·s-1;年浮尘、扬沙日数呈波动式上升趋势,年沙尘暴日数呈缓慢下降趋势;年风蚀气候因子平均为28.3。     

内蒙古科尔沁沙地临界起沙阈值的范围确定

临界起沙阈值可表征地表土壤的可蚀性,是风蚀起沙研究中非常重要的物理量之一。基于微气象学方法,将沙尘浓度和垂直沙尘通量均开始增加且至少持续0.5 h所对应的摩擦速度(或风速)确定为临界起沙摩擦速度u_*t(或临界起沙风速U_t)。利用内蒙古科尔沁沙地地区2010-2013年春季大气环境综合观测资料,分析了不同沙尘天气过程(扬沙、沙尘暴和强沙尘暴)起沙阶段沙尘浓度和垂直沙尘通量随摩擦速度的演变特征,精细确定了该地区临界起沙摩擦速度(u_*t)和临界起沙风速(U_t)的范围分别为0.45±0.20和6.5±3.0 m/s,同时讨论了不同起沙判据对确定临界起沙阈值产生的影响。相比而言,采用的起沙判据尽可能地排除了沙尘输送和沉降过程的影响,适用于不同的沙尘天气类型,使沙尘粒子进入大气的起沙结果更趋于合理,其结果可为建立统一、合理的起沙判据提供参考。     

An overview of tropical cyclone and tropical meteorology research progress

There has been much progress in the study of tropical cyclones and tropical meteorology in China in the past few years. A new atmospheric field experiment of tropical cyclone landfall with the acronym of CLATEX (China Landfalling Typhoon Experiment) was implemented in July-August 2002. The boundary layer characteristics of the target typhoon Vongfong and the mesoscale structural features of other landfalling typhoons were studied. In addition, typhoon track operational forecasting errors in the last decade have been reduced because the operational monitoring equipment and forecast techniques were improved.Some results from the research program on tropical cyclone landfall, structure and intensity change, intensification near coastal waters, interaction between tropical cyclone and mid-latitude circulation, and the interaction among different scales of motion are described in this paper. Four major meteorological scientific experiments in China with international cooperation were implemented in 1998: the South China Sea monsoon field experiment (SCSMEX), the Tibetan Plateau field experiment (TIPEX), the Huaihe River basin energy and water cycle experiment (HUBEX), and the South China heavy rain scientific experiment(HUAMEX). Although these field experiments have different scientific objectives, they commonly relate to monsoon activities and they interact with each other. The valuable intensive observation data that were obtained have already been shared internationally. Some new findings have been published recently.Other research work in China, such as the tropical air-sea interaction, tropical atmospheric circulation,and weather systems, axe reviewed in this paper as well. Some research results have shown that the rainfall anomalies for different regions in China were closely related to the stages of E1 Nifio events.     

南方夏秋干旱期间的天气气候特征

对40多年来南方的天气气候特征进行了分析,提出了7～9月夏秋干旱期形成干旱的主要天气系统为西太平洋副热带高压.从干燥度和降水的空间分布综合分析,得出了南方最旱区位于湖南、江西中部.广西、贵州、湖南西北和东南山区、江西南部山区、安徽南部山区、福建-浙江沿海交界山区和苏北沿海为湿润区,人工增雨潜力较大.特殊地形所形成的焚风效应是形成湘中干旱不可忽略的原因.为南方夏秋期间对流云降水潜力研究和科学实施人工增雨作业提供一定依据.     

Environmental significance of RSL in ancient city wall: historical desertification of Ordos Plateau, Northern China

Scholars in China have long debated whether the desertification during the past two millennia of the Ordos Plateau was caused primarily by climatic or anthropogenic factors. Focusing on the ancient cities of the Ordos Plateau, and especially on the discovery of Rammed Sand Layer (RSL) in the city wall which proved to be from sand dunes by grain size and scan electron microscope analysis, this study combined the use of historical records and methods of environmental archaeology to clarify the history of the deserts on the Ordos Plateau. The results indicated that some of the ancient cities were built originally in the desert, thus failing to represent a good condition of landscape. Therefore, abandonment of these cities cannot be simply attributed to anthropogenic desertification.     

局地经圈环流和沙漠

应用 Xie和 Arkin降水资料和 NECP／NCAR再分析资料，研究了撒哈拉和中国西北沙漠地区的干旱气候。结果表明，尽管该两区域都有在年降水量少于50mm的十分干旱的区域，但其年度特征却非常不同。在撒哈拉沙漠中心的南部地区和中国西北沙漠地区，超过70％的降水出现在6－8月；而在撒哈拉沙漠中心以北地区，降水主要集中在12－2月。这种十分干旱的气候不能用Channey提出的生物圈－辐射效应加以解释。由于6－7月的强下沉中心远在撒哈拉强干中心的北部，其形成也不能用Rodwell和Hoskins提出的季风－沙漠机制予以解释。利用局地经圈环流的概念对两地干旱气候的分析和比较发现，局地经圈环流的下沉在12－2月支配着局地的垂直环流，导致干旱气候形成。这时撒哈拉北部的弱的、相对的多雨的气候是因受中海气候型影响所改。而在6－7月局地该为上升运动，其中尤以中国西北地区为显著。因此撒哈拉南部及中国西北的沙漠地区降水多集中在6－8月。不过与此上升运动相伴的是低空来之中、高纬的强而干的北风，它携带的水汽甚少，不利深对流发展。正是这种局地经圈环流导致了该两处干旱气候的形成。     

德州一次沙尘天气过程成因及气溶胶粒子的输送路径分析

利用NCEP 1°×1°再分析资料分析了2017年5月4日浮尘和5月5日扬沙天气的成因。结果表明：3日20时—4日08时,蒙古气旋在有利的环流背景下迅速发展,配合冷锋在内蒙古中部和东部形成大范围的强沙尘天气;4日20时—5日08时沙尘通过高空气流输送到华北地区,在自身沉降和较强下沉气流的共同作用下,迅速沉降形成华北地区大范围的浮尘天气;5日08—14时由于西北路冷空气影响,横槽转竖,冷锋加速南下,将大量沙源地的沙尘输送到德州造成扬沙天气。通过HYSPLIT模式对本次过程中气团后向轨迹的模拟,证实以上两个阶段沙尘天气过程中的输送方式及路径。通过分析影响系统、物理量和气象要素发现,蒙古国、我国内蒙古中部沙源地天气系统强度、位置的变化直接影响沙尘天气的类型,高层气流变化与沙尘天气的类型有很好的对应关系。     

绿洲、沙漠及戈壁边界层特征对比分析

利用黑河实验所取得的资料，对比分析了绿洲、沙漠及戈壁边界层中风、温、湿分布规律，从而为研究西北地区不同下垫面所造成的气候特点对生态环境的影响、土地的开发腹及人工改造自然环境等工作提供依据。     

Multi-Model Projection of July–August Climate Extreme Changes over China under CO_2 Doubling. Part II: Temperature

This is the second part of the authors’ analysis on the output of 24 coupled climate models from the Twentieth-Century Climate in Coupled Models (20C3M) experiment and 1% per year CO 2 increase experiment (to doubling) (1pctto2x) of phase 3 of the Coupled Model Inter-comparison Project (CMIP3). The study focuses on the potential changes of July–August temperature extremes over China. The pattern correlation coefficients of the simulated temperature with the observations are 0.6–0.9, which are higher than the results for precipitation. However, most models have cold bias compared to observation, with a larger cold bias over western China (>5°C) than over eastern China (<2°C). The multi-model ensemble (MME) exhibits a significant increase of temperature under the 1pctto2x scenario. The amplitude of the MME warming shows a northwest–southeast decreasing gradient. The warming spread among the models (～1°C– 2°C) is less than MME warming (～2°C–4°C), indicating a relatively robust temperature change under CO 2 doubling. Further analysis of Geophysical Fluid Dynamics Laboratory coupled climate model version 2.1 (GFDL-CM2.1) simulations suggests that the warming pattern may be related to heat transport by summer monsoons. The contrast of cloud effects also has contributions. The different vertical structures of warming over northwestern China and southeastern China may be attributed to the different natures of vertical circulations. The deep, moist convection over southeastern China is an effective mechanism for "transporting" the warming upward, leading to more upper-level warming. In northwestern China, the warming is more surface-orientated, possibly due to the shallow, dry convection.     

海气相互作用对“格美”台风发展的影响研究

西北太平洋是全球唯一一年四季都有热带气旋生成的海域,同时,我国沿海紧临该海域,是受热带气旋影响最为严重的国家之一.本文通过建立海气耦合模式,以西北太平洋西边界流系源区为研究区域,通过对"格美"台风的数值模拟结果分析,研究海气相互作用对热带气旋发展的影响,对提高台风的数值模拟及预报水平有重要意义.研究表明:耦合作用引起的...     

Seasonal variations in Dustfall and its iron content over North China

Extensive dustfall collections were carried out from April 2001 to May 2002 in North China. The highest level of dustfall occurred in the Gobi deserts and at the margins of sandy deserts in the region. The iron content in dustfall in North China varied from 0.6% to 6.0% and there was significant seasonal variation, which indicates the dust sources differed during the year. Although the iron content in dustfall in North China is higher in the Loess Plateau and arable lands and lower in the Gobi and sandy deserts, the total iron deposition was higher in the Gobi desert regions. If the fine particles （PM10） in dustfall in North China are the major contributors of dust transport to eastern China and western parts of the North Pacific, then the annual deposition rates of iron may have been underestimated in previous studies. Our analysis indicates that iron deposition may reach 1.38 × 10^3 to 2.43 × 10^3 kg km^-2 and that most iron deposition occurs in spring and summer. If the more-coarse fractions （PM50） are considered, deposition rates may reach 2.75 × 10^3 and 6.80 × 10^3 kg km^-2, which would represent a large source of iron deposition in eastern China and the western North Pacific.     

Simulation of the global bio-geophysical interactions during the Last Glacial Maximum

 The bio-geophysical feedbacks during the Last Glacial Maximum (LGM, 21 000 y BP) are investigated by use of an asynchronously coupled global atmosphere-biome model. It is found that the coupled model improves on the results of an atmosphere-only model especially for the Siberian region, where the inclusion of vegetation-snow-albedo interaction leads to a better agreement with geological reconstructions. Furthermore, it is shown that two stable solutions of the coupled model are possible under LGM boundary conditions. The presence of bright sand desert at the beginning of a simulation leads to more extensive subtropical deserts, whereas an initial global vegetation cover with forest, steppe, or dark desert results in a northward spread of vegetation of up to some 1000 km, mainly in the western Sahara. These differences can be explained in the framework of Charney’s theory of a “self-induction” of deserts through albedo enhancement. Moreover, it is found that the tropical easterly jet is strengthened in the case of the “green” Sahara, which in turn leads to a modification of the Indian summer monsoon. Received: 20 June 1997/Accepted: 14 January 1998