An investigation of sand–dust storm events and land surface characteristics in China using NOAA NDVI data

Observations from 560 weather stations in China show that sand–dust storms occur most frequently in April in north China. The region consists of Sub-dry Mid Temperate, Dry Mid Temperate, Sub-dry South Temperate and Dry South Temperate Zones and much of the land surface is desert or semi-desert: it is relatively dry with minimal rainfall and a high annual mean temperature. In most regions of China, the annual mean frequency of sand–dust events decreased sharply between 1980 and 1997 and then increased from 1997 to 2000. Statistical analyses demonstrate that the frequency of sand–dust storms correlates highly with wind speed, which in turn is strongly related to land surface features; on the other hand, a significant correlation between storm events and other atmospheric quantities such as precipitation and temperature was not observed. Accordingly, land surface cover characteristics (vegetation, snowfall and soil texture) may play a significant role in determining the occurrence of sand–dust storms in China. Analysis of Normalized Difference Vegetation Index derived from National Oceanic and Atmospheric Administration and Empirical Orthogonal Function show that since 1995 surface vegetation cover in large areas of Northern China has significantly deteriorated. Moreover, a high correlation is shown to exist among the annual occurrence of sand–dust storms, surface vegetation cover and snowfall. This suggests that the deterioration of surface vegetation cover may strongly influence the occurrence of sand–dust storms in China. Soils with coarse and medium textures are found to be more associated with sand–dust storms than other soils.     

Seasonally frozen soil effects on the dynamic behavior of highway bridges

Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, bridge stiffness is also measurably higher in winter months. Significant changes due to seasonal freezing in bridge pier boundary conditions require additional detailing in order to ensure a ductile performance of the bridge during a design earthquake event. This paper reports the latest results obtained from a project that systematically investigated the effects of seasonally frozen soil on the seismic behavior of highway bridges in cold regions. A bridge was chosen and was monitored to study its seismic performance and assess the impact of seasonally frozen soil on its dynamic properties. A Finite Element (FE) model was created for this bridge to analyze the impact of seasonal frost. It was found that when frost depth reaches 1.2 m, the first transverse modal frequency increases about 200% when compared with the no-frost case. The results show that seasonal frost has a significant impact on the overall dynamic behavior of bridges supported by pile foundations in cold regions, and that these effects should be accounted for in seismic design.     

CINRAD/SA雷达开关组件故障分析处理

根据广州CINRAD／SA雷达发射机开关组件的一起故障现象,结合信号流程、电路原理图,深入元件一级,对故障的定位、检测及排除过程作了详细介绍,并对故障的成因作了推断分析,最后就雷达维护方面总结了一些经验,旨在对雷达技术保障人员提供参考和借鉴。     

鹤壁市夏季一次雹暴过程的成因分析

运用天气图、物理量场、卫星云图、雷达回波及相关气象资料,分析了2005年6月19日发生在鹤壁的雷雨大风、并伴有局地冰雹的强对流天气过程.结果表明:在低层θse高能舌区内,地面冷锋移到 500 hPa高空急流出口区下方左侧时,高低空次级环流耦合,触发不稳定能量释放、产生强烈的上升运动,是这次强对流天气产生的直接原因.     

探空资料在地面云观测中的应用

云的观测在地面观测中非常重要,为了提高地面人工观测云的准确性,利用气象台站的探空资料,对相应时段的地面观测数据中的低、中、高三族云进行校对应用,增加目测云的准确性,减少因人为因素而造成的观测误差;并阐明探空资料应用于地面云观测中的可行性。     

高光谱遥感影像分类研究进展

随着模式识别、机器学习、遥感技术等相关学科领域的发展,高光谱遥感影像分类研究取得快速进展。本文系统总结和评述了当前高光谱遥感影像分类的相关研究进展,在总结分类策略的基础上,重点从以核方法为代表的新型分类器设计、特征挖掘、空间-光谱分类、基于主动学习和半监督学习的分类、基于稀疏表达的分类、多分类器集成六个方面对高光谱影像像素级分类最新研究进行了综述。针对今后的研究方向,指出高光谱遥感影像分类一方面要适应大数据、智能化高光谱对地观测的发展前沿,继续引入机器学习领域的新理论、新方法,综合利用多源遥感数据、多维特征空间互补的优势,提高分类精度、分类器泛化能力和自动化程度;另一方面要关注高光谱遥感应用的需求,突出高光谱遥感记录精细光谱特征的优势,针对应用需求发展有效的分类方法。     

青藏高原大尺度地表流体的重力效应特征分析

基于2002~2017年三维大气再分析模型、水文模式及GRACE卫星重力数据,采用负荷格林函数和卫星重力反演方法分析青藏高原大尺度地表流体的重力效应特征。结果表明,青藏高原地区大气扣除季节项前后的重力效应峰对峰变化介于1.9~10.7 μGal和1.1~4.6 μGal,其负荷效应呈现出显著的季节性特征;土壤水和积雪扣除季节项前后的重力效应峰对峰变化介于0.9~9.9 μGal和0.7~8.3 μGal,其负荷效应呈现出显著的季节性和年际变化特征;GRACE时变重力场扣除季节项前后的重力变化峰对峰变化介于4.4~24.1 μGal和3.4~18.3 μGal,考虑观测误差、构造运动和信号泄漏误差的影响,其显著的季节性和年际变化反映了多种地表流体的综合影响。     

2015年10月4日佛山龙卷过程的观测分析

受1522号台风彩虹外围螺旋云带影响,2015年10月4日15时28分—16时（北京时）广东佛山出现了EF3级强龙卷并造成严重灾害。为了综合分析龙卷发生的多尺度环境背景场和龙卷的结构及强度变化等特点,进行了灾情调研,航拍龙卷灾情路径,走访龙卷目击者,确认龙卷路径及灾情级别,再结合多渠道获取的龙卷视频照片等资料以及观测资料进行分析研究,结果表明:（1）产生此次龙卷的超级单体存在于台风彩虹外围螺旋云带内;龙卷向西北偏北方向移动,触地时长为32 min,受灾路径长度为31.7 km,最大受灾直径为577 m,平均速度约为60 km/h,具有“移动速度快,影响范围广,破坏力强”的特点,其移动速度快慢似与超级单体强度和地面的粗糙度有关。（2）佛山地区中高层受偏南气流控制,水汽充足,地面有弱冷空气;珠三角喇叭口地形有利于气流的辐合与局地涡旋的产生;抬升凝结高度低,风垂直切变大,有利于龙卷的生成。（3）地面自动气象站气象要素表现出受龙卷环流影响的特征。3 s极大风速的大值带和3 s最低气压的低值带以及1 h累计降水大值中心呈现出与龙卷走向一致的东南—西北向带状分布;龙卷到来时其周围自动气象站气温和气压明显降低,风速明显增大,风向明显改变;降水在龙卷靠近前5—10分钟就开始明显增大,其大值中心位于龙卷路径的西侧。龙卷离开后气压比龙卷来临前有所升高,但气温较前降低。（4）龙卷出现在钩状回波前进方向的右后侧;降水大值区与雷达组合反射率大值区基本一致。地面风场的辐合中心与龙卷触地的位置基本一致,并且钩状回波的入流区与地面偏东风区相对应。龙卷风暴单体发展高度在4 km左右,具有低重心对流的特点。其前部存在回波悬垂,一条很窄的向西北倾斜的回波大值带可能与龙卷漏斗云墙有关。对应径向速度剖面图上为一条向西北倾斜的正、负速度交界区,构成一个逆时针旋转的涡旋带,切向剖面图上存在较强的辐合。（5）龙卷发展过程中伴随着龙卷风暴顶和风暴底的逐渐下降以及单体质心的下降,中气旋与龙卷涡旋特征的顶和底也随之逐渐下降。龙卷风涡旋特征的顶高和底高都略低于中气旋,并在龙卷触地时降至最低。龙卷涡旋的切变值远大于中气旋的切变值,且在龙卷强度最强时最大。      

Comparison in diversity of eukaryotic algae in surface sediments from different functional sea areas of Qingdao coast,the Yellow Sea,China: a metabarcoding approach

Journal of Oceanology and Limnology - Surface sediment samples were collected in three different functional sea areas in Qingdao coast, East China, including the inner Jiaozhou Bay, the Laoshan...     

英国约克郡( Yo rkshire Dale)国家公园钙华苔藓植物群落研究

报道英国约克郡国家公园5个钙华沉积地点苔藓植物群落调查结果。该区域钙华苔藓群落共13个,由12科15属18种组成。区系地理成分由北温带和世界广布两种成分组成;生活型以垫状矮丛集型和交织型占优势。根据钙华沉积环境特征,划分Cron钙华苔藓群落、洞穴钙华苔藓群落、瀑华苔藓群落、峭壁钙华苔藓群落和泉华苔藓群落等5种类型。调查结果表明,研究区现代苔藓植物群落钙华沉积作用十分显著。