Accuracy of the linearized standard balance and asymmetric balance systems in a shallow-water numerical model     

Ingo Slch  J. Dominique Mller  Lloyd J. Shapiro 《Dynamics of Atmospheres and Oceans》2007,44(2):77-103

A numerical evaluation of the accuracy of the standard balance equations (BE) and the asymmetric balance equations (AB) in strong vortex applications is presented. Linearized equations for the evolution of disturbances on a symmetric hurricane-like vortex in a shallow-water model are used to compare forecasts using the AB and BE formulations with benchmark primitive equation forecasts. The validity of the BE and AB models is formally determined by the square of the Froude number, F², and the square of the local Rossby number for disturbances with azimuthal wavenumber n, , respectively. The numerical experiments demonstrate that accurate results can be achieved with BE and AB in situations where F² and , respectively, are not necessarily small. When the divergence of the asymmetric disturbance is not much smaller than its vorticity, and the azimuthal wavenumber of the disturbance is low, the AB system proves to be a useful alternative to BE.  相似文献   

Influence of upper air conditions on the Patagonia icefields   总被引：1，自引：1，他引：0  

L.A. Rasmussen  H. Conway  C.F. Raymond 《Global and Planetary Change》2007,59(1-4):203

Upper-air conditions archived in the NCEP-NCAR Reanalysis have been used to investigate changes in precipitation and snowfall over the Patagonia icefields during 1960–99. Apparently, whereas total precipitation has not changed, warming has caused a decrease in the amount falling as snow. Precipitation at a site is taken to be proportional to the product of the relative humidity and the component of the wind in a particular critical direction, both at 850 hPa ( 1400 m) at a point over the ocean to the west of the icefields; whether it falls as rain or snow is assumed to depend on whether the temperature at the elevation of the site is above or below + 2 °C. The critical direction is assumed to be 270°, which is perpendicular to the north–south trending Andes and is also the prevailing wind direction in this zone of strong westerlies. Because of the scarcity of precipitation records on or near the icefields, the constant of proportionality cannot be determined, so the investigation is limited to examining relative changes in those upper air variables. Warming at 850 hPa has been 0.5 °C over the 40 years, both winter and summer, with the effects that it has: (1) shifted from snow to rain 5% of the precipitation, the total of which has changed little, and (2) increased annual melt in the ablation areas by 0.5 m w.e. The icefields have been losing mass since at least 1870, so this 40-year trend represents only an acceleration of the longer-term trend of adjusting to climate change since the Little Ice Age.  相似文献   

基流分割在水文计算中的应用——确定泉水流量     

夏凡  许伟林  蒋南杰 《城市地质》2010,5(2):42-44

本文运用基流分割法确定鱼卡盆地泉水流量,联合水量平衡法还原鱼卡河上站流量系列资料,为鱼卡盆地水资源评价奠定了基础。  相似文献   

Lower Hybrid Wave Electron Heating in the Fast Solar Wind     

J. Martin Laming 《Astrophysics and Space Science》2005,298(1-2):385-388

We discuss electron–ion equilibration by lower hybrid waves in the fast solar wind, and its observed effects upon element charge state distributions.  相似文献   

环境资源与生态系统的关系   总被引：1，自引：1，他引：0  

刘立国  王洁  赵剑强 《地球科学与环境学报》2005,27(3):104-106

采用论述、图解及数学关系式的方法，较深入地分析了资源、环境与生态系统的关系。认为环境要素可分为仅产生污染型影响的环境要素；既可以产生污染型影响又可以导致资源破坏型影响的环境要素；仅产生资源破坏型影响3种类型。自然环境的优劣由组成自然环境各环境要素的环境质量状况和可作为自然环境要素的自然资源的数量多少决定。要实现环境与经济的可持续发展，应该把环境质量和资源利用同时作为衡量环境优劣的因素。  相似文献   

Towards an energy‐based runoff generation theory for tundra landscapes     

William L. Quinton  Sean K. Carey 《水文研究》2008,22(23):4649-4653

Runoff hydrology has a large historical context concerned with the mechanisms and pathways of how water is transferred to the stream network. Despite this, there has been relatively little application of runoff generation theory to cold regions, particularly the expansive treeless environments where tundra vegetation, permafrost, and organic soils predominate. Here, the hydrological cycle is heavily influenced by 1) snow storage and release, 2) permafrost and frozen ground that restricts drainage, and 3) the water holding capacity of organic soils. While previous research has adapted temperate runoff generation concepts such as variable source area, transmissivity feedback, and fill‐and‐spill, there has been no runoff generation concept developed explicitly for tundra environments. Here, we propose an energy‐based framework for delineating runoff contributing areas for tundra environments. Aerodynamic energy and roughness height control the end‐of‐winter snow water equivalent, which varies orders of magnitude across the landscape. Radiant energy in turn controls snowmelt and ground thaw rates. The combined spatial pattern of aerodynamic and radiant energy control flow pathways and the runoff contributing areas of the catchment, which are persistent on a year‐to‐year basis. While ground surface topography obviously plays an important role in the assessment of contributing areas, the close coupling of energy to the hydrological cycles in arctic and alpine tundra environments dictates a new paradigm. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Hydrological processes of a rainforest headwater swamp from natural chemical tracing in Nsimi watershed,Cameroon     

Jean‐Christophe Maréchal  Jean‐Jacques Braun  Jean Riotte  Jean‐Pierre Bedimo Bedimo  Jean‐Loup Boeglin 《水文研究》2011,25(14):2246-2260

The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end‐member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall events of the wet season, the pre‐event water comprises a mix of 80% of bedrock aquifer and 20% of swamp aquifer. During storms, the relative contribution of overland flow increases according to the rainfall intensity and the initial saturation rate of the pre‐event water reservoirs. The yearly contribution of overland flow from the swamp to the stream is about 31%. The relationship between the swamp and the stream fluctuates with space and time. Generally, the swamp is drained by the stream; however, at the end of long dry seasons, after the first rains, indirect recharge occurs from the stream to the swamp with a hydraulic gradient inversion in the swamp aquifer. The net contribution of the swamp aquifer to the stream is only 4%, which is much lower than the hillside aquifer contribution of about 65%. Recharge on the swamp being very low, these results suggest that, except for a few storms at the end of the dry season, the Nsimi swamp does not contribute to flood attenuation. Evapotranspiration is higher on the hillside than in the swamp. Nevertheless, depletion of water stored within the swamp is dominated by evaporation rather than by its contribution to streamflow. The export of solutes through swamp groundwater flow below the weir is low (<7%). Nevertheless, the swamp is the most active area of weathering in the watershed. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Modelling agricultural nitrogen contributions to the Jiulong River estuary and coastal water   总被引：5，自引：0，他引：5  

Wenzhi Cao  Huasheng Hong  Shiping Yue 《Global and Planetary Change》2005,47(2-4):111

The geographical setting of the Jiulong River estuary determines that the estuary receives wastes from both riverine input and adjacent urban sewage. However, the dominant nitrogen (N) source remains unclear. A nutrient mass-balance model and a preliminary LOICZ (Land–Ocean Interactions in the Coastal Zone) biogeochemical model were linked to evaluate agricultural N contributions from the Jiulong River catchment to the estuary and coastal water. Results showed that agricultural N surplus was the largest N source in the catchment, contributing 60.87% of the total Nitrogen (N) and 68.63% of the dissolved inorganic nitrogen (DIN). Household wastes and other sources followed. Riverine DIN fluxes were about 20.3% of exportable DIN and 14.4% of exportable total N, but approximately 9.7% of DIN inputs, and 7.3% of total N inputs to the Jiulong River catchment. The model system clearly showed that agricultural and anthropogenic activities in the catchment were the major N sources of the estuary and coastal water, and riverine N fluxes from these sources substantially impacted the estuary and coastal water quality and biogeochemical processes.  相似文献   

Modelling lake stage and water balance of Lake Tana,Ethiopia     

Yirgalem A. Chebud  Assefa M. Melesse 《水文研究》2009,23(25):3534-3544

The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three‐dimensional finite‐difference ground‐water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

A soil‐water‐balance approach to quantify groundwater recharge from irrigated cropland in the North China Plain     

Eloise Kendy  Pierre Grard‐Marchant  M. Todd Walter  Yongqiang Zhang  Changming Liu  Tammo S. Steenhuis 《水文研究》2003,17(10):2011-2031

Rapidly depleting unconfined aquifers are the primary source of water for irrigation on the North China Plain. Yet, despite its critical importance, groundwater recharge to the Plain remains an enigma. We introduce a one‐dimensional soil‐water‐balance model to estimate precipitation‐ and irrigation‐generated areal recharge from commonly available crop and soil characteristics and climate data. To limit input data needs and to simplify calculations, the model assumes that water flows vertically downward under a unit gradient; infiltration and evapotranspiration are separate, sequential processes; evapotranspiration is allocated to evaporation and transpiration as a function of leaf‐area index and is limited by soil‐moisture content; and evaporation and transpiration are distributed through the soil profile as exponential functions of soil and root depth, respectively. For calibration, model‐calculated water contents of 11 soil‐depth intervals from 0 to 200 cm were compared with measured water contents of loam soil at four sites in Luancheng County, Hebei Province, over 3 years (1998–2001). Each 50‐m² site was identically cropped with winter wheat and summer maize, but received a different irrigation treatment. Average root mean‐squared error between measured and model‐calculated water content of the top 180 cm was 4·2 cm, or 9·3% of average total water content. In addition, model‐calculated evapotranspiration compared well with that measured by a large‐scale lysimeter. To test the model, 12 additional sites were simulated successfully. Model results demonstrate that drainage from the soil profile is not a constant fraction of precipitation and irrigation inputs, but rather the fraction increases as the inputs increase. Because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage will not reverse water‐table declines. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献