Radar Data Assimilation for the Simulation of Mesoscale Convective Systems     

Jo-Han LEE  Dong-Kyou LEE  Hyun-Ha LEE  Yonghan CHOI  Hyung-Woo KIM 《大气科学进展》2010,27(5):1025-1042

A heavy rainfall case related to Mesoscale Convective Systems (MCSs) over the Korean Peninsula was selected to investigate the impact of radar data assimilation on a heavy rainfall forecast. The Weather Research and Forecasting (WRF) three-dimensional variational (3DVAR) data assimilation system with tuning of the length scale of the background error covariance and observation error parameters was used to assimilate radar radial velocity and reflectivity data. The radar data used in the assimilation experiments were preprocessed using quality-control procedures and interpolated/thinned into Cartesian coordinates by the SPRINT/CEDRIC packages. Sensitivity experiments were carried out in order to determine the optimal values of the assimilation window length and the update frequency used for the rapid update cycle and incremental analysis update experiments. The assimilation of radar data has a positive influence on the heavy rainfall forecast. Quantitative features of the heavy rainfall case, such as the maximum rainfall amount and Root Mean Squared Differences (RMSDs) of zonal/meridional wind components, were improved by tuning of the length scale and observation error parameters. Qualitative features of the case, such as the maximum rainfall position and time series of hourly rainfall, were enhanced by an incremental analysis update technique. The positive effects of the radar data assimilation and the tuning of the length scale and observation error parameters were clearly shown by the 3DVAR increment.  相似文献   

冻融循环作用下边坡地震动稳定性研究     

王文丽  王兰民  郑龙 《震灾防御技术》2013,8(2):156-163

季节冻土区和多年冻土区边坡在经历冻融循环后其力学性质产生较大变化,边坡稳定性随之改变,在地震动荷载作用下存在着巨大的安全隐患.本文基于FLAC数值软件,将考虑冻土相变的显热熔算法引入热学计算模块,并结合静态边界动力计算模块,建立了适用于冻融循环条件下的边坡地震动稳定性分析平台.研究了冻融循环对边坡土体地震动稳定性的影响.结果表明,在发生冻融循环的季节冻土区或多年冻土已经退化的区域,地震动后边坡的塑性破坏形式主要取决于发生冻融循环的活动层的范围.  相似文献   

Mindful Learning in Geography: Cultivating Balanced Attitudes Toward Regions     

《The Journal of geography》2012,111(5):197-210

This study examines the potential of mindful learning in geography education. A hypothesis was developed to form the research topic, and three experiments were performed to analyze it. The experiments supported the hypothesis. In other words, mindful learning was found to be helpful for cultivating balanced attitudes toward regions. In conclusion, mindful learning has the potential to be a simple but helpful method of geography education.  相似文献   

基于Kriging算法实现等高线制式转换   总被引：1，自引：0，他引：1       下载免费PDF全文

马俊  吕晓华  尉伯虎 《海洋测绘》2009,29(4):35-37

地图上等高线的等高距主要有英美制（英尺、码）和公制（米）两种制式，不同制式间的等高线转换，其实质是等高线重构。克里金（Kriging）算法是对空间分布的离散数据进行无偏、线性最优内插估计的一种较理想的插值方法。论述了Kriging算法的基本原理，并以VB＋Surfer为二次开发环境，实现了等高线制式由码至米的转换，分析了该方法应用的主要特点。  相似文献   

三江平原湿地植物群落P、K的积累、动态及其生物循环   总被引：9，自引：0，他引：9  

何太蓉  杨永兴 《海洋与湖沼》2006,37(2):178-183

在三江平原湿地植物生长季节里,选择该区分布最广、面积最大且最具有代表性的毛果苔草(Carexlasioncarpa)-狭叶甜茅(Glyceria spiculosa)群落和小叶章(Deyeuxia angustifo-lia)群落为研究对象,逐月测定两类湿地群落生物量,并对植物样品分别用钼锑抗比色法和原子吸收法测定其P、K含量。在此基础上,探讨了两类湿地群落的P、K积累量及其生物循环特征。结果表明,三江平原不同的植物群落以及同一群落的不同器官,其P、K元素积累量不同,而且都有明显的季节变化。根是群落中P、K元素的最大贮存器官,其P、K积累量占总量的80%左右。湿地群落中K的吸收量、归还量、存留量、现存量和表土贮量都大于P的对应值,同时K的利用系数和循环系数均大于P,毛果苔草-狭叶甜茅群落K的吸收系数大于P,而小叶章群落K的吸收系数小于P。  相似文献   

海洋沉积物中氮的形态及其生态学意义     

吕晓霞  宋金明 《海洋科学集刊》2003,(45):101-111

海洋沉积物作为生源要素氮的重要源与汇，在其生物地球化学循环中起着至关重要的作用。该项研究旨在查清海洋沉积物中氮的存在形态及其生态学意义。氮是生物生命活动必需的营养要素，海洋中的氮往往是海洋初级生产力的限制因子，氮的吸收与再生释放在估算海洋新生产力和生源要素的生物地球化学循环率上也有重要贡献。海洋沉积物中的氮作为海水中氮的重要供给源是海洋生物赖以生存的重要物质基础，对维持海洋生态平衡、修复失衡的海洋生态环境具有重要意义。但由于不同海区海洋沉积物的来源和环境不同，氮的形态和含量亦不相同，可被生物吸收和利用的数量就不相同，因此造成了不同海区生物种群和环境不同，进而影响生态环境。因此，研究海洋沉积物中氮的形态，了解各个形态与沉积物中生物种群及与环境的关系，确定其生物和化学活性，査清氮不同形态的生态学功能，对于深入探讨海洋生物资源可持续利用的方法和策略具有重要意义。本文主要阐述海洋沉积物中氮的存在形式与分布、氮的早期成岩和去营养化作用、硝化和反硝化作用以及氮与生物特定种群的关系等，探讨了影响海洋沉积物中的氮循环的主要因素，并分析了海洋沉积物中的氮与生态系的关系，以期对研究氮的海洋生物地球化学过程有所帮助。  相似文献   

Nutrient Cycling and a Stoichiometric Model in Epidavros, a Deep Basin in the Aegean Sea     

Nicholas  Friugos 《Marine Ecology》1986,7(1):43-57

Abstract. The nutrient cycling of Epidavros, a deep basin in the Saronikos Gulf, was studied in relation to various environmental factors during 1973–1976 at a station characterized by stagnant conditions. The regeneration of nutrients was related to the consumption of oxygen, and a seasonal nutrient cycle occurred with low nutrient concentrations in the spring and summer, followed by high nutrient levels in autumn and winter. In addition high values of nitrate and silicate were observed in the deeper waters, which tended to be anoxic, although the water masses were renewed during spring 1974. The distribution pattern of nutrients together with nutrient ratios were compared with previous studies of the same and neighbouring areas as well as of other isolated basins. A stoichiometric model indicates that plankton organisms in the Epidavros basin have approximate atomic ratios for C: N: P of 150: 14:1, while the ratio of change for nitrogen and phosphorus in the water is only 8.8:1 by atoms. This is probably because of the slow rate of regeneration of nitrogenous material and/or assimilation and regeneration in organic forms. The water/plankton relation in the Epidavros basin appears to be very similar to that in the Baltic Sea.  相似文献   

弦图的团复盖和邻域复盖     

吴举林 《中国海洋大学学报(自然科学版)》1991,(1)

证明了弦图的团二分图是子树二分图,从而把弦图上一般形式的团复盖问题化为弦图上的对点团复盖,可以在多项式时间内求解。对强弦图上的邻域复盖问题,本文提出两条求解途径:一是化为弦图上的团复盖问题,一是化为可用组合方法求解的线性规划问题。  相似文献   

Heavy metals distribution in mangrove sediments along the mobile coastline of French Guiana   总被引：1，自引：0，他引：1  

C. Marchand  E. Lallier-Vergès  F. Baltzer  P. Albéric  D. Cossa  P. Baillif 《Marine Chemistry》2006

The accumulation of nine heavy metals in fine-grained sediments from the mangrove fringed coast of French Guiana is evaluated. The dynamic features of the South American tropical coastline, from the Amazon to the Orinoco Rivers, result in mangrove sediments being alternately submitted to phases of erosion and net sedimentation a few tens of years long. This process influences the distribution of the heavy metals associated with these frequently re-mobilized deposits. Sedimentary cores and mangrove plant samples were collected, at different seasons, in various swamps characterized by different properties (content of sedimentary organic matter, distance from sea water and fresh water). The ranges of measured concentrations expressed in μmol g^− 1 were the following: Cu (0.06 to 0.61), Co (0.12 to 0.68), Pb (0.08 to 0.18), Ni (0.32 to 0.76), Cr (0.61 to 1.40), Zn (1.25 to 5.94), Mn (4.36 to 45.4) and Fe (441 to 1128). No differences were found between sediments from mangroves developing upstream and downstream of urban areas, i.e. Cayenne and Kourou. This suggests that the content of mangrove sediments in heavy metals along the coastline of French Guiana is essentially the result of the continuous alternation of accumulation and transport phases occurring upstream after departing from the Amazon watershed. The sources of this heavy metals content are thus difficult to identify. However it is well known that the alluvium produced by the natural erosion of the Amazonian soils is naturally enriched in mercury. Also, the run-off from gold mining activities is known to contribute to mercury pollution. Ranges in total Hg were between 0.15 and 2.57 nmol g^− 1, with mean values close to 0.41 nmol g^− 1, and were clearly correlated with total organic carbon except for some outstanding high values, which may be a result of rapid geochemical changes. Heavy metal concentrations showed variations with depth. The redox conditions and the decay processes affecting the organic matter control the cycling of iron and manganese, which in turn control the concentrations and associations of heavy metals. These preliminary results suggest that the variations in heavy metal content with depth or between mangrove areas result largely from diagenetic processes rather than changes in metal input resulting from local human activities.  相似文献   

Nitrogen cycling in deep-sea sediments of the Porcupine Abyssal Plain, NE Atlantic   总被引：2，自引：0，他引：2  

Jenny Brunnegrd  Sibylle Grandel  Henrik Sthl  Anders Tengberg  Per O.J. Hall 《Progress in Oceanography》2004,63(4):159-181

Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH₄) and nitrate (NO₃) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO₃, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with ¹⁴C-based sediment accumulation rates and dry bulk density. Average NH₄ and NO₃-effluxes were 7.4 ± 19 μmol m⁻² d⁻¹ (n = 7) and 52 ± 30 μmol m⁻² d⁻¹ (n = 14), respectively, during the period 1996–2000. During the same period, the DON-flux was 11 ± 5.6 μmol m⁻² d⁻¹ (n = 5) and the denitrification rate was 5.1 ± 3.0 μmol m⁻² d⁻¹ (n = 22). Temporal and spatial variations were only found in the benthic NO₃ fluxes. The average burial rate was 4.6 ± 0.9 μmol m⁻² d⁻¹. On average over the sampling period, the recycling efficiency of the PON input to the sediment was 94% and the burial efficiency hence 6%. The DON flux constituted 14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year⁻¹, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3–12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.  相似文献