The Relation Between Humidity and Liquid Water Content in Fog: An Experimental Approach   总被引：1，自引：0，他引：1  

Stefan Georg Gonser  Otto Klemm  Frank Griessbaum  Shih-Chieh Chang  Hou-Sen Chu  Yue-Joe Hsia 《Pure and Applied Geophysics》2012,169(5-6):821-833

Microphysical measurements of orographic fog were performed above a montane cloud forest in northeastern Taiwan (Chilan mountain site). The measured parameters include droplet size distribution (DSD), absolute humidity (AH), relative humidity (RH), air temperature, wind speed and direction, visibility, and solar short wave radiation. The scope of this work was to study the short term variations of DSD, temperature, and RH, with a temporal resolution of 3?Hz. The results show that orographic fog is randomly composed of various air volumes that are intrinsically rather homogeneous, but exhibit clear differences between each other with respect to their size, RH, LWC, and DSD. Three general types of air volumes have been identified via the recorded DSD. A statistical analysis of the characteristics of these volumes yielded large variabilities in persistence, RH, and LWC. Further, the data revealed an inverse relation between RH and LWC. In principle, this finding can be explained by the condensational growth theory for droplets containing soluble or insoluble material. Droplets with greater diameters can exist at lower ambient RH than smaller ones. However, condensational growth alone is not capable to explain the large observed differences in DSD and RH because the respective growth speeds are too slow to explain the observed phenomena. Other mechanisms play key roles as well. Possible processes leading to the large observed differences in RH and DSD include turbulence induced collision and coalescence, and heterogeneous mixing. More analyses including fog droplet chemistry and dynamic microphysical modeling are required to further study these processes. To our knowledge, this is the first experimental field observation of the anti-correlation between RH and LWC in fog.  相似文献   

Evaluation of remotely‐sensed DEMs and modification based on plausibility rules and initial sediment budgets of an artificially‐created catchment     

Anna Schneider  Horst H. Gerke  Thomas Maurer  Stefan Seifert  Rossen Nenov  Reinhard F. Hüttl 《地球表面变化过程与地形》2012,37(7):708-725

To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely‐sensed DEMs for an improved quantification of initial sediment mass changes in an artificially‐created catchment. DEMs were constructed from photogrammetry‐based, airborne (ALS) and ground‐based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three‐dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region‐by‐region for rill, interrill and alluvial areas, based on logical and hydro‐geomorphological principles. Additional DEMs were constructed by combining multi‐source, modified data. Models were evaluated by comparison with d‐GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry‐based DEMs were suited to quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited to rill areas, while ALS DEMs performed best in vegetation‐covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry‐ and TLS‐based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro‐geomorphic surface structures can be better represented by applying region‐specific modifications. Photogrammetry‐based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro‐geomorphic evolution. Results of the critical comparative evaluation of remotely‐sensed elevation data can help to better interpret DEM‐based quantifications of earth‐surface processes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Effects of pollen leaching and microbial degradation on organic carbon and nutrient availability in lake water     

Stefan?R?sel  Anna?Rych?a  Christian?Wurzbacher  Hans-Peter?GrossartEmail author 《Aquatic Sciences - Research Across Boundaries》2012,74(1):87-99

Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus and total dissolved nitrogen (up to 0.04 and 1.5 mg L⁻¹, respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for ≥80, ≥40, ≥50% for organic C, N and P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of temperate lakes. This requires further attention in aquatic ecology.  相似文献   

Guidelines for sampling bedload transport with minimum uncertainty          下载免费PDF全文

Roy M. Frings  Stefan Vollmer 《Sedimentology》2017,64(6):1630-1645

The stability of river channels and their suitability as habitat for aqueous organisms is strongly controlled by the rate of bedload transport. Quantification of bedload transport rates in rivers is difficult, not only because of the temporal variation in transport, but also because of the cross‐channel variation in transport. The objectives of this study were: (i) to determine the effect of cross‐channel variation in bedload transport on the uncertainty of width‐integrated transport rates; and to use this knowledge (ii) to improve guidelines for bedload sampling. This was done through a thorough statistical evaluation of stochastic and systematic uncertainties involved in bed‐load transport measurements. Based on this evaluation, new guidelines are presented for determination of the number of samples and sampling positions across the channel that are required for bedload measurements in several types of sand‐bed rivers and gravel‐bed rivers. The guidelines relate to bedload measurements made with pressure‐difference (Helley‐Smith type) samplers that require numerous bedload samples of short duration at several positions across the channel. The results show that generally more sampling positions across the channel are required in gravel‐bed rivers than in sand‐bed rivers. For gravel‐bed rivers with unknown cross‐channel distribution of transport, at least 10 sampling positions are recommended, whereas for most sand‐bed rivers five positions suffice. In addition, at least 12 short‐duration samples are required at each position to obtain bedload estimates with uncertainties below 20%. If the same level of uncertainty is desired in the case of high spatial and temporal variation in transport rates, the number of short‐duration samples needed per sampling position increases to 40.  相似文献   

Orientation information in wayfinding instructions: evidences from human verbal and visual instructions     

Vanessa Joy A. Anacta  Angela Schwering  Rui Li  Stefan Muenzer 《GeoJournal》2017,82(3):567-583

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Assessment of agri-spillways as a soil erosion protection measure in Mediterranean sloping vineyards   总被引：2，自引：1，他引：1  

Jesús Rodrigo-Comino  Stefan Wirtz  Eric C. Brevik  José D. Ruiz-Sinoga  Johannes B. Ries 《山地科学学报》2017,14(6):1009-1022

Suitable vineyard soils enhance soil stability and biodiversity which in turn protects roots against erosion and nutrient losses. There is a lack of information related to inexpensive and suitable methods and tools to protect the soil in Mediterranean sloping vineyards(25° of slope inclination). In the vineyards of the Montes de Málaga(southern Spain), a sustainable land management practice that controls soil erosion is actually achieved by tilling rills in the down-slope direction to canalize water and sediments. Because of their design and use, we call them agri-spillways. In this research, we assessed two agri-spillways(between 10 m and 15 m length, and slopes between 25.8° and 35°) by performing runoff experiments under extreme conditions(a motor driven pump that discharged water flows up to 1.33 l s~(-1) for 12 to 15 minutes: ≈1000 l). The final results showed: i) a great capacity by these rills to canalize large amounts of water and sediments; and, ii) higher water flow speeds(between 0.16 m s-1 and 0.28 m s~(-1)) and sediment concentrationrates(up to 1538.6 g l~(-1)) than typically found in other Mediterranean areas and land uses(such as badlands, rangelands or extensive crops of olives and almonds). The speed of water flow and the sediment concentration were much higher in the shorter and steeper rill. We concluded that agri-spillways, given correct planning and maintenance, can be a potential solution as an inexpensive method to protect the soil in sloping Mediterranean vineyards.  相似文献   

Micro‐geomorphology determines community structure of biological soil crusts at small scales     

Xin‐Rong Li  Min‐Zhu He  Stefan Zerbe  Xiao‐Jun Li  Li‐Chao Liu 《地球表面变化过程与地形》2010,35(8):932-940

Biological soil crusts (BSCs) are ubiquitous communities of diminutive organisms such as cyanobacteria, green algae, lichens, mosses and others associated closely with particles of surface soil, forming a cohesive thin horizontal layer. The ecological roles of BSCs affecting soil nutrient cycling, stability and hydrological processes, influencing the germination and establishment of vascular plants, and serving as habitats for numerous arthropods and microorganism have been well documented. We tested the hypothesis that micro‐geomorphological features determine the spatial distribution of BSCs by reallocating related abiotic resources at small‐ and medium‐scales in the Tengger Desert. Our results showed that higher soil pH and higher total potassium content in topsoil positively correlated with the colonization of cyanobacteria and algae in the earliest successional stages of BSCs, while increasing dust deposition onto the topsoil enhanced the development of lichen and mosses in the later stages of BSCs. Increasing soil moisture raised the proportion of mosses and lichen in BSCs, this will possibly change the ecological functions of BSCs, such as nitrogen‐fixation by cyanobacteria, due to the conversion from a complex to relative simple type of BSC. Micro‐geomorphology has created various habitats at a small‐scale affecting colonization and development of cryptogams. This paper considers the contribution of micro‐geomorphology to biodiversity in the extreme arid desert systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

On characterizing the temporal dominance patterns of model parameters and processes   总被引：1，自引：0，他引：1       下载免费PDF全文

Björn Guse  Matthias Pfannerstill  Michael Strauch  Dominik E. Reusser  Stefan Lüdtke  Martin Volk  Hoshin Gupta  Nicola Fohrer 《水文研究》2016,30(13):2255-2270

Diagnostic analyses of hydrological models intend to improve the understanding of how processes and their dynamics are represented in models. Temporal patterns of parameter dominance could be precisely characterized with a temporally resolved parameter sensitivity analysis. In this way, the discharge conditions are characterized, that lead to a parameter dominance in the model. To achieve this, the analysis of temporal dynamics in parameter sensitivity is enhanced by including additional information in a three‐tiered framework on different aggregation levels. Firstly, temporal dynamics of parameter sensitivity provide daily time series of their sensitivities to detect variations in the dominance of model parameters. Secondly, the daily sensitivities are related to the flow duration curve (FDC) to emphasize high sensitivities of model parameters in relation to specific discharge magnitudes. Thirdly, parameter sensitivities are monthly averaged separately for five segments of the FDC to detect typical patterns of parameter dominances for different discharge magnitudes. The three methodical steps are applied on two contrasting catchments (upland and lowland catchment) to demonstrate how the temporal patterns of parameter dynamics represent different hydrological regimes. The discharge dynamic in the lowland catchment is controlled by groundwater parameters for all discharge magnitudes. In contrast, different processes are relevant in the upland catchment, because the dominances of parameters from fast and slow runoff components in the upland catchment are changing over the year for the different discharge magnitudes. The joined interpretation of these three diagnostic steps provides deeper insights of how model parameters represent hydrological dynamics in models for different discharge magnitudes. Thus, this diagnostic framework leads to a better characterization of model parameters and their temporal dynamics and helps to understand the process behaviour in hydrological models. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Preface to the special issue “Strategic applications of real-time risk mitigation strategies and tools: case studies and lessons learned in REAKT”     

Carlo Cauzzi  Paolo Gasparini  Stefan Wiemer  Jochen Zschau 《Bulletin of Earthquake Engineering》2016,14(9):2437-2439

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Late Glacial ice advances in southeast Tibet     

Stefan Strasky  Angela A. Graf  Zhizhong Zhao  Peter W. Kubik  Heinrich Baur  Christian Schlüchter  Rainer Wieler 《Journal of Asian Earth Sciences》2009,34(3):458-465

The sensitivity of Tibetan glacial systems to North Atlantic climate forcing is a major issue in palaeoclimatology. In this study, we present surface exposure ages of erratic boulders from a valley system in the Hengduan Mountains, southeastern Tibet, showing evidence of an ice advance during Heinrich event 1. Cosmogenic nuclide analyses (¹⁰Be and ²¹Ne) revealed consistent exposure ages, indicating no major periods of burial or pre-exposure. Erosion-corrected (3 mm/ka) ¹⁰Be exposure ages range from 13.4 to 16.3 ka. This is in agreement with recalculated exposure ages from the same valley system by [Tschudi, S., Schäfer, J.M., Zhao, Z., Wu, X., Ivy-Ochs, S., Kubik, P.W., Schlüchter, C., 2003. Glacial advances in Tibet during the Younger Dryas? Evidence from cosmogenic ¹⁰Be, ²⁶Al, and ²¹Ne. Journal of Asian Earth Sciences 22, 301–306.]. Thus this indicates that local glaciers advanced in the investigated area as a response to Heinrich event 1 cooling and that periglacial surface adjustments during the Younger Dryas overprinted the glacial morphology, leading to deceptively young exposure ages of certain erratic boulders.  相似文献