Negative water vapour skewness and dry tongues in the convective boundary layer: observations and large-eddy simulation budget analysis     

F. Couvreux  F. Guichard  V. Masson  J.-L. Redelsperger 《Boundary-Layer Meteorology》2007,123(2):269-294

This study focuses on the intrusion of dry air into the convective boundary layer (CBL) originating from the top of the CBL. Aircraft in-situ measurements from the IHOP_2002 field campaign indicate a prevalence of negative skewness of the water vapour distribution within the growing daytime CBL over land. This negative skewness is interpreted according to large-eddy simulations (LES) as the result of descending dry downdrafts originating from above the mixed layer. LES are used to determine the statistical properties of these intrusions: their size and thermodynamical characteristics. A conditional sampling analysis demonstrates their significance in the retrieval of moisture variances and fluxes. The rapid CBL growth explains why greater negative skewness is observed during the growing phase: the large amounts of dry air that are quickly incorporated into the CBL prevent a full homogenisation by turbulent mixing. The boundary-layer warming in this phase also plays a role in the acquisition of negative buoyancy for these dry tongues, and thus possibly explains their kinematics in the lower CBL. Budget analysis helps to identify the processes responsible for the negative skewness. This budget study underlines the main role of turbulent transport, which distributes the skewness produced at the top or the bottom of the CBL into the interior of the CBL. The dry tongues contribute significantly to this turbulent transport.  相似文献   

Occurrence and Resistance of Pathogenic Bacteria Along the Tietê River Downstream of São Paulo in Brazil     

Wolf-Rainer Abraham  Alexandre José Macedo  Luiz Humberto Gomes  Flavio C. A. Tavares 《洁净——土壤、空气、水》2007,35(4):339-347

The load of pathogenic bacteria, their fate and their dangerousness in the Tietê River were assessed along 100 km starting from the city of São Paulo, Brazil. The data were compared with those from two German rivers. High loads of pathogens were found in the Tietê River near the city of São Paulo (Escherichia coli O157:H7, Shigella flexneri, and Shigella boydii), which were absent 30 km downstream of São Paulo. The antibiotic resistances observed in the Tietê river were rather low and decreased after the major input in São Paulo to significantly lower levels about 30 km downstream. While the Brazilian isolates were more susceptible for ampicillin than the German ones, the reverse was observed for gentamycin. For optimal control of infections in humans critical areas where these bacteria survived longer and their elimination mechanisms should be identified as well as the extent and the origin of antibiotic resistance should be determined.  相似文献   

地理信息服务质量(QoGIS):概念和研究框架   总被引：2，自引：0，他引：2  

吴华意  章汉武 《武汉大学学报(信息科学版)》2007,32(5):385-388

在探讨地理数据特点的基础上，提出了地理信息服务质量（QoGIS）的概念和研究框架，设计了一个体现地理信息服务质量的原型系统架构。  相似文献   

大比例尺土地利用数据库建设有关技术问题的探讨     

胡兴树  杨宏山 《测绘科学》2007,32(Z1):85-87

地籍调查、村集体土地所有权调查和土地利用调查对调查底图的要求不同,在土地利用数据库建设的过程中应综合考虑;GPS、GIS和RS技术的应用,改变了土地利用调查的技术流程,提高了调查效率;土地利用数据库质量控制包括质量检查方法、质量标准和质量责任体系。  相似文献   

陕西省特殊用煤资源分布特征及清洁利用方向     

李聪聪  魏云迅  杜芳鹏 《中国煤炭地质》2020,(2):22-28,66

陕西省煤炭资源丰富,煤类分布齐全,以陕西省煤炭规划矿区为评价单元,在对矿区主要煤层煤岩煤质特征分析的基础上,参照特殊用煤资源潜力评价指标体系,对陕西省14个煤炭规划矿区液化、气化及焦化用煤资源进行了初步划分,结果表明:陕西省直接液化用煤和气化用煤资源丰富,焦化用煤相对较少,气化用煤主要分布于黄陇侏罗纪煤田黄陵矿区、旬耀矿区、彬长矿区和永陇矿区,陕北侏罗纪煤田的神府矿区、榆神矿区、榆横矿区以及陕北石炭-二叠系古城矿区;焦化用煤主要分布于渭北石炭-二叠纪煤田铜川矿区、蒲白矿区、澄合矿区和韩城矿区中高阶烟煤分布区,液化用煤主要分布于府谷矿区、榆横矿区、神府矿区、榆神矿区等低阶长焰煤分布地区;为陕西省煤化工产业布局和煤炭资源清洁高效利用提供了方向。  相似文献   

Climate extremes in Loess of China coupled with the strength of deep-water formation in the North Atlantic   总被引：1，自引：0，他引：1  

Zhengtang Guo  Tungsheng Liu  Nicolas Fedoroff  Lanying Wei  Zhongli Ding  Naiqin Wu  Huoyuan Lu  Wenying Jiang  Zhisheng An 《Global and Planetary Change》1998,18(3-4)

The loess-paleosol sequences of the last 1.2 Ma in China have recorded two kinds of climate extremes: the strongly developed S4, S5-1 and S5-3 soils (corresponding to the marine δ¹⁸O stages 11, 13, and 15, respectively) as evidence of three episodes of great warmth and two coarse-grained loess units (L9 and L15, corresponding to the marine δ¹⁸O stages 22, 23, 24 and 38, respectively) which indicate severest glacial conditions. The climatic and geographical significance of these events are still unclear, and their cause remains a puzzle.Paleopedological, geochemical and magnetic susceptibility data from three loess sections (Xifeng, Changwu and Weinan) suggest that the S4, S5-1 and S5-3 soils were formed under sub-tropical semi-humid climates with a tentatively estimated mean annual temperature (MAT) of at least 4–6°C higher and a mean annual precipitation (MAP) of 200–300 mm higher than for the present-day, indicating a much strengthened summer monsoon. The annual rainfall was particularly accentuated for the southern-most part of the Loess Plateau, suggesting that the monsoon rain belt (the contact of the monsoonal northward warm-humid air mass with the dry-cold southward one) might have stood at the southern part of the Plateau for a relatively long period each year. The loess units L9 and L15 were deposited under semi-desertic environments with a tentatively estimated MAT and MAP of only about 1.5–3°C and 150–250 mm, indicating a much strengthened winter monsoon, and that the summer monsoon front could rarely penetrate into the Loess Plateau region.Correlation with marine carbon isotope records suggests that these climate extremes have large regional, even global, significance rather than being local phenomena in China. They match the periods with greatest/smallest Atlantic–Pacific δ¹³C gradients, respectively, indicating their relationships with the strength of Deep Water (NADW) production in the North Atlantic. These results suggest that the monsoon climate in the Loess Plateau region was significantly linked with the North Atlantic thermohaline circulation on timescales of 10⁴ years.  相似文献   

计算机跟踪伺服系统的保护电路     

李阳  雷成明 《紫金山天文台台刊》1998,17(1):83-85

本文介绍了为紫台13.7米射电望远镜跟踪系统设计制造的一套的简单实用的保护电路。实验证明该电路性能可靠、效果显著。  相似文献   

Impedance characteristics of carbon steel under cathodic protection   总被引：1，自引：0，他引：1  

李言涛  侯保荣 《中国海洋湖沼学报》1998,16(1):60-63

INTRODUCTIONInpraCticalengineeringapplicati0ns,thecormsionofstalundercathodicprotalioncanbecontr0llediftheproodi0np0tenhalisset2O()t03(X)mVnegativewithaspeCttothenatamlcormsi0np0tenial(MasatSugi,l976,Takehiko,l972).Theprotalnp0tentia1edinpraedcalapplicationisbedonexperienceandtheory.Tooru(l985,l986)foundthattheopbocathodicproodionpotentialcoinddedwiththepotentialwhenpolarhati0nresistancemaxndnd,s0thiscoinedencecanbeedt00btainoptbore-sultforcarbonstalundercathodicpronaion.Inthiswork,the…  相似文献   

Conservation of wetlands especially as waterfowl habitat in northeast China   总被引：2，自引：0，他引：2  

刘红玉 《中国地理科学(英文版)》1998,8(3):281-288

Ｗｅｔｌａｎｄ,ｗｉｔｈｖｅｒｙｈｉｇｈｂｉｏｌｏｇｉｃａｌｐｒｏｄｕｃｔｉｖｉｔｙ,ｔｒｅｍｅｎｄｏｕｓｒｅｓｏｕｒｃｅｐｏｔｅｎｔｉａｌａｎｄｅｎｖｉｒｏｎｍｅｎｔｆｕｎｃｔｉｏｎ,ｉｓａｓｐｅｃｉａｌｅｃｏｓｙｓｔｅｍｉｎｔｈｅｅａｒｔｈａｎ...  相似文献   

砼地基施工质量的CT检测技术     

郭玉松 《河南国土资源》1998,(3)

建筑工程板状砼地基属地下工程,其施工质量的检测与控制难度较大。根据该类工程的特点（面积大,厚度小）,可将其视为二维结构,采用弹性波ＣＴ成像方法检测其施工质量,在工程实践中取得了满意的效果。本文将结合工程实例介绍板状砼地基浇注质量的ＣＴ检测技术,包括弹性波ＣＴ的基本原理、野外数据采集系统的设计以及数据处理方法。  相似文献