Lightning activity related to satellite and radar observations of a mesoscale convective system over Texas on 7–8 April 2002     

Nikolai Dotzek  Robert M. Rabin  Lawrence D. Carey  Donald R. MacGorman  Tracy L. McCormick  Nicholas W. Demetriades  Martin J. Murphy  Ronald L. Holle 《Atmospheric Research》2005,76(1-4):127

A multi-sensor study of the leading-line, trailing-stratiform (LLTS) mesoscale convective system (MCS) that developed over Texas in the afternoon of 7 April 2002 is presented. The analysis relies mainly on operationally available data sources such as GOES East satellite imagery, WSR-88D radar data and NLDN cloud-to-ground flash data. In addition, total lightning information in three dimensions from the LDAR II network in the Dallas–Ft. Worth region is used.GOES East satellite imagery revealed several ring-like cloud top structures with a diameter of about 100 km during MCS formation. The Throckmorton tornadic supercell, which had formed just ahead of the developing linear MCS, was characterized by a high CG+ percentage below a V-shaped cloud top overshoot north of the tornado swath. There were indications of the presence of a tilted electrical dipole in this storm. Also this supercell had low average CG− first stroke currents and flash multiplicities. Interestingly, especially the average CG+ flash multiplicity in the Throckmorton storm showed oscillations with an estimated period of about 15 min.Later on, in the mature LLTS MCS, the radar versus lightning activity comparison revealed two dominant discharge regions at the back of the convective leading edge and a gentle descent of the upper intracloud lightning region into the trailing stratiform region, apparently coupled to hydrometeor sedimentation. There was evidence for an inverted dipole in the stratiform region of the LLTS MCS, and CG+ flashes from the stratiform region had high first return stroke peak currents.  相似文献   

Geostatistical analysis of the effects of stage and roughness on reach-scale spatial patterns of velocity and turbulence intensity     

Carl J. Legleiter  Tracy L. Phelps  Ellen E. Wohl 《Geomorphology》2007,83(3-4):322-345

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Deglacial meltwater drainage and glaciodynamics: inferences from Laurentide eskers, Canada     

Dr. Tracy A. Brennand   《Geomorphology》2000,32(3-4)

This paper evaluates current knowledge of Laurentide eskers in Canada in the light of developments in glacier hydrology and glacial sedimentology. Questions regarding the morpho-sedimentary relations of eskers, the synchroneity and operation of R-channel systems, the role of supraglacial meltwater input and proglacial water bodies, the controls on esker pattern, and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed. A morphologic classification of eskers is proposed. Five types of eskers are identified and investigated. Type I eskers likely formed in extensive, synchronous, dendritic R-channel networks under regionally stagnant ice that terminated in standing water. Type II eskers likely formed in short, subaqueously terminating R-channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation. Type III eskers plausibly formed in short R-channels that drained either to interior lakes in, or tunnel channels under, regionally stagnant ice. Type IV eskers may have formed as time-transgressive segments in short, subaerially terminating R-channels (or reentrants) that developed close to the ice margin as the ice front underwent stagnation-zone retreat or downwasted and backwasted regionally (stagnant ice); however, formation in synchronous R-channels cannot be discounted on the basis of reported observations. Type V eskers may have formed in H-channels that terminated subaerially. The spatial distribution of these esker types is discussed. The factors that determined Laurentide R-channel pattern and operation were likely a complex combination of (i) supraglacial meltwater discharge, (ii) the number and location of sink holes, (iii) the ice surface slope, thickness and velocity, and (iv) the permeability, topography and rigidity of the bed. These factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle.  相似文献   

Contributing sources to baseflow in pre‐alpine headwaters using spatial snapshot sampling          下载免费PDF全文

Benjamin M. C. Fischer  Michael Rinderer  Philipp Schneider  Tracy Ewen  Jan Seibert 《水文研究》2015,29(26):5321-5336

Mountainous headwaters consist of different landscape units including forests, meadows and wetlands. In these headwaters it is unclear which landscape units contribute what percentage to baseflow. In this study, we analysed spatiotemporal differences in baseflow isotope and hydrochemistry to identify catchment‐scale runoff contribution. Three baseflow snapshot sampling campaigns were performed in the Swiss pre‐alpine headwater catchment of the Zwäckentobel (4.25 km²) and six of its adjacent subcatchments. The spatial and temporal variability of δ²H, Ca, DOC, AT, pH, SO₄, Mg and H₄SiO₄ of streamflow, groundwater and spring water samples was analysed and related to catchment area and wetland percentage using bivariate and multivariate methods. Our study found that in the six subcatchments, with variable arrangements of landscape units, the inter‐ and intra catchment variability of isotopic and hydrochemical compositions was small and generally not significant. Stream samples were distinctly different from shallow groundwater. An upper spring zone located near the water divide above 1,400 m and a larger wetland were identified by their distinct spatial isotopic and hydrochemical composition. The upstream wetland percentage was not correlated to the hydrochemical streamflow composition, suggesting that wetlands were less connected and act as passive features with a negligible contribution to baseflow runoff. The isotopic and hydrochemical composition of baseflow changed slightly from the upper spring zone towards the subcatchment outlets and corresponded to the signature of deep groundwater. Our results confirm the need and benefits of spatially distributed snapshot sampling to derive process understanding of heterogeneous headwaters during baseflow. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Field reconnaissance and overview of the impact of Hurricane Matthew on Haiti’s Tiburon Peninsula     

Tracy L. Kijewski-Correa  Andrew B. Kennedy  Alexandros A. Taflanidis  David O. Prevatt 《Natural Hazards》2018,93(2):627-659

The old potable water network in Byblos city is provided mainly from Ibrahim River nearby. Located in a seismic region, the aging network needs to tolerate seismic threats; thus, damage to the potable water network needs to be assessed. Therefore, first, enhancing infrastructure resilience is briefly discussed, noting briefly the need to bridge specifically between heritage risk management and engineering. Second, Byblos potable water network, seismicity, and geology are detailed. Third, the potable water network damage assessment methodology is presented. It encompasses hazard assessment, network inventory, damage functions, and model development. Data and maps are prepared using the Geographic Information System and then modeled in Ergo platform to obtain the damage to buried pipelines in the event of likely earthquake scenarios. Ergo is updated to consider recommended ground motion prediction equations (GMPEs) for the Middle East region, to consider amplification of the peak ground velocity in hazard maps due to different soil types, and to consider adequate fragility functions. Moreover, different Byblos geotechnical maps, landslide hazard, and liquefaction are investigated and embedded. Damage results to pipelines are dependent on the hazard maps obtained using different GMPEs and geotechnical maps. Asbestos cement pipelines will be most damaged, followed by polyethylene and then by ductile iron. Finally, recommendations are offered to consider an improved sustainable rehabilitation solution. The study provides a better understanding of Byblos potable water network and allows the establishment of a sustainable and resilience-to-earthquake preparedness strategy and recovery plan.  相似文献   

Correct treatment of rotation of sliding surfaces in a kinematic model of the triple friction pendulum bearing     

Tracy C. Becker  Stephen A. Mahin 《地震工程与结构动力学》2013,42(2):311-317

This paper addresses the treatment of the rotation of the internal components of the triple friction pendulum (TFP) isolation bearing in a numerical model previously presented by the authors. The numerical model is based on the kinematic behavior of the individual sliding surfaces and the constitutive relationships between them. The modification suggested in this paper improves the performance of the model so that the results exactly match that of the one‐dimensional piecewise linear behavior previously derived for the TFP bearing for restricted properties. The improved numerical model simulates bidirectional shear response and places no a priori restrictions on the bearing properties. The modification is put in the form of a technical communication so that the notation used and the basis of the correction could be presented with adequate clarity and so that an example of the benefit of the correction could be presented. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Approximating peak responses in seismically isolated buildings using generalized modal analysis     

Tracy C. Becker  Stephen A. Mahin 《地震工程与结构动力学》2013,42(12):1807-1825

Although the ability to simulate accurately the detailed behavior of nonlinear isolation bearings and the effects of this nonlinearity on dynamic response of the isolated building is desirable, such detailed analyses are not feasible during initial design stages when bearing properties are being selected. However, it would be very beneficial to be able to estimate accurately key engineering demand parameters at the early stages of design to understand the dynamic response characteristics of the isolated structure and to balance and optimize the bearing and structural characteristics to achieve the performance goals set for the building. Unfortunately, classical modal response spectrum analysis methods do not provide accurate results for problems with large, nonclassical damping, as is characteristic of isolated buildings. To find a method capable of predicting peak building responses even with large nonclassical damping, generalized modal response spectrum analysis is implemented. The responses of several buildings having different heights and isolated by linear viscous as well as triple friction pendulum and single friction pendulum isolation systems are investigated. Generalized modal response spectrum analysis methods were found to give significantly better predictions for all systems compared with classical methods. The behavior of buildings isolated with single friction pendulum systems exhibiting sudden changes in stiffness could not be well predicted by either general or classical modal response spectrum analysis when effective damping was increased. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Fusion of Radar and Optical Data for Land Cover Mapping     

Nathaniel D. Herold  Barry N. Haack 《国际地球制图》2013,28(2):21-30

Abstract

This study examined the complementarity of radar and optical data for feature identification. Spaceborne radar and Landsat Thematic Mapper (TM ) multispectral data sets were assessed independently and in combination to classify a site near Wad Medani, Sudan. Radar processing procedures included speckle reduction, texture extraction and post‐processing smoothing. Relative accuracy of the resultant classifications was established by comparison to ground truth information derived from field visitation. Neither speckle filtering nor post‐classification smoothing were improvements over the poor results obtained with the unfiltered, original radar data. Texture measures were significant improvements over the original data (20 percent overall accuracy increase) and several, but not all, individual classes had excellent results. Landsat TM had good overall results (80 percent correct) but considerable spectral confusion between urban and bare soil. Combination of radar with Landsat TM greatly improved results, achieving near perfect classification of all individual classes. The systematic strategy of this study, determination of the best individual method before introducing the next procedure, was effective in managing a complex set of analysis possibilities.  相似文献   

Comparison and Integration of Radar and Optical Data for Land Use/Cover Mapping     

Nathaniel D. Herold  Barry N. Haack 《国际地球制图》2013,28(4):9-19

Abstract

This study examined the complementarity of spaceborne radar and optical data for surface feature identification. RADARSAT data sets were assessed independently and in combination with Landsat Thematic Mapper (TM) multispectral data. The primary methodology was spectral signature extraction and the application of a statistical decision rule to classify the surface features for a site near Kericho, Kenya. Relative accuracy of the resultant classifications was established by digital integration and comparison to reference information derived from field visitation. Speckle filtering was a great improvement over the poor results achieved with the unfiltered, original radar data but still not adequate for accurate land cover classification. The extraction and use of Variance texture measures was found to be very advantageous. The overall results were not significant improvements over speckle removal (6% increase) but several individual classes, forest and urban, had excellent results with texture. Combinations of radar with Landsat TM greatly improved results, achieving near perfect classification of all individual classes. The highest overall accuracy was achieved with a merger that included the best individual texture image and six reflectance bands of the TM data. The systematic strategy of this study, determination of the best individual method before introducing the next procedure, was effective in managing a very complex, almost infinite set of analysis possibilities.  相似文献   

A Review of “Why “Where” Matters: Understanding and Profiting from GPS,GIS, and Remote Sensing”     

Barry Haack 《The Professional geographer》2013,65(2):310-312

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