Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas   总被引：1，自引：1，他引：0  

Christoph W. Kent  Sue Grimmond  Janet Barlow  David Gatey  Simone Kotthaus  Fredrik Lindberg  Christos H. Halios 《Boundary-Layer Meteorology》2017,164(2):183-213

Nine methods to determine local-scale aerodynamic roughness length \((z_{0})\) and zero-plane displacement \((z_{d})\) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial \(z_{d}\) and \(z_{0}\) estimates. Across the three sites, \(z_{d}\) varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating \(z_{d}\) is consistently greater than the local mean building height. Depending upon method and wind direction, \(z_{0}\) varies between 0.1 and 5 m with morphometric \(z_{0}\) consistently being 2–3 m larger than the anemometric \(z_{0}\). No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine \(z_{d}\) and \(z_{0}\).  相似文献   

Safe separation distance score: a new metric for evaluating wildland firefighter safety zones using lidar     

Michael J. Campbell  Philip E. Dennison  Bret W. Butler 《International journal of geographical information science》2017,31(7):1448-1466

Safety zones are areas where firefighters can retreat to in order to avoid bodily harm when threatened by burnover or entrapment from wildland fire. At present, safety zones are primarily designated by firefighting personnel as part of daily fire management activities. Though critical to safety zone assessment, the effectiveness of this approach is inherently limited by the individual firefighter’s or crew boss’s ability to accurately and consistently interpret vegetation conditions, topography, and spatial characteristics of potential safety zones (e.g. area and geometry of a forest clearing). In order to facilitate the safety zone identification and characterization process, this study introduces a new metric for safety zone evaluation: the Safe Separation Distance Score (SSDS). The SSDS is a numerical representation of the relative suitability of a given area as a safety zone according to its size, geometry, and surrounding vegetation height. This paper describes an algorithm for calculating pixel-based and polygon-based SSDS from lidar data. SSDS is calculated for every potential safety zone within a lidar dataset covering Tahoe National Forest, California, USA. A total of 2367 potential safety zones with an SSDS ≥1 were mapped, representing areas that are suitable for fires burning in low wind and low slope conditions. The highest SSDS calculated within the study area was 9.65, a score that represents suitability in the highest wind-steepest slope conditions. Potential safety zones were clustered in space, with areas in the northern and eastern portions of the National Forest containing an abundance of safety zones while areas to the south and west were completely devoid of them. SSDS can be calculated for potential safety zones in advance of firefighting, and can allow firefighters to carefully compare and select safety zones based on their location, terrain, and wind conditions. This technique shows promise as a standard method for objectively identifying and ranking safety zones on a spatial basis.  相似文献   

Mass data processing of time series Landsat imagery: pixels to data products for forest monitoring     

Txomin Hermosilla  Michael A. Wulder  Joanne C. White  Nicholas C. Coops  Geordie W. Hobart  Lorraine B. Campbell 《International Journal of Digital Earth》2016,9(11):1035-1054

Free and open access to the Landsat archive has enabled the implementation of national and global terrestrial monitoring projects. Herein, we summarize a project characterizing the change history of Canada’s forested ecosystems with a time series of data representing 1984–2012. Using the Composite2Change approach, we applied spectral trend analysis to annual best-available-pixel (BAP) surface reflectance image composites produced from Landsat TM and ETM+ imagery. A total of 73,544 images were used to produce 29 annual image composites, generating ～400 TB of interim data products and resulting in ～25 TB of annual gap-free reflectance composites and change products. On average, 10% of pixels in the annual BAP composites were missing data, with 86% of pixels having data gaps in two consecutive years or fewer. Change detection overall accuracy was 89%. Change attribution overall accuracy was 92%, with higher accuracy for stand-replacing wildfire and harvest. Changes were assigned to the correct year with an accuracy of 89%. Outcomes of this project provide baseline information and nationally consistent data source to quantify and characterize changes in forested ecosystems. The methods applied and lessons learned build confidence in the products generated and empower others to develop or refine similar satellite-based monitoring projects.  相似文献   

Effects of Tree Size,Shade Tolerance,and Spatial Pattern on the Mortality of Woody Plants in a Seminatural Forest in Central Kentucky     

Daehyun Kim  Julian J. N. Campbell 《The Professional geographer》2016,68(3):436-450

Previous biogeographical research has investigated the mortality of woody plants, emphasizing tree size, shade tolerance, and competition individually as critical factors. Few researchers, though, have empirically evaluated the simultaneous and relative importance of these three factors in a single study. Based on a thirty-five-year study within the University of Kentucky Arboretum, we report that none of the factors exerted an overriding influence on the tree survivorship alone. Rather, they were tightly intertwined in a complex way. Our study indicates that the three factors have contributed perhaps equally or at least simultaneously to the overall demographic processes in the woodland.  相似文献   

A history of violence: magma incubation,timing and tephra distribution of the Los Chocoyos supereruption (Atitlán Caldera,Guatemala)     

Alejandro Cisneros de León  Julie C. Schindlbeck-Belo  Steffen Kutterolf  Martin Danišík  Axel K. Schmitt  Armin Freundt  Wendy Pérez  Janet C. Harvey  Kuo-Lung Wang  Hao-Yang Lee 《第四纪科学杂志》2021,36(2):169-179

The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization ²³⁸U–²³⁰Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 ⁺¹⁶/₋₁₄ ka) and I-Fall eruptions (56 ^+8.2/_−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km³ is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.  相似文献   

Modified passive capillary samplers for collecting samples of snowmelt infiltration for stable isotope analysis in remote,seasonally inaccessible watersheds 1: laboratory evaluation     

Marty D. Frisbee  Fred M. Phillips  Andrew R. Campbell  Jan M. H. Hendrickx 《水文研究》2010,24(7):825-833

Snowmelt is the most significant source of runoff generation and recharge in many of the mountainous watersheds worldwide and this is especially true in the southwestern United States. Yet, the isotopic and geochemical composition of the soil–meltwater endmember remains poorly constrained. Using the isotopic compositions of snow and snowmelt runoff samples taken from the landscape surface as proxies for soil–meltwater endmembers is problematic since they are typically not representative of the actual composition of soil meltwater. Furthermore, the applicability of current methodologies to collect the isotopic composition of meltwater is limited because of the remote and often seasonally inaccessible nature of the terrain where snowpacks develop. Therefore, a robust methodology requiring little maintenance or monitoring is desirable. A lab experiment was conducted to determine the suitability of using a modified passive capillary sampler (M‐PCAPS) design to collect snowmelt infiltration for isotopic analysis. Passive capillary samplers are constructed from fiberglass wicks that can be installed in the soil to sample vadose‐zone waters under a wide range of matric potentials and require little maintenance. Results from this lab experiment indicate that the wicking process associated with M‐PCAPS does not fractionate water but certain precautions are necessary to prevent exchange between the wick and the atmosphere. In this experiment, M‐PCAPS effectively tracked the changing isotopic composition of a soil reservoir undergoing evaporation. Therefore, M‐PCAPS provide a robust methodology to sample the isotopic composition of snowmelt infiltration in remote watersheds and similar applications. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

On the coattails of climate? Opportunities and threats of a warming Earth for biodiversity conservation     

Shannon Hagerman  Rebecca Witter  Catherine Corson  Daniel Suarez  Edward M. Maclin  Maggie Bourque  Lisa Campbell 《Global Environmental Change》2012,22(3):724-735

The relationship between climate change and biodiversity was a central issue at the 10th Conference of the Parties (COP 10) to the Convention on Biological Diversity (CBD). In this paper we draw from participant observation data collected at COP 10, and related policy documentation, to examine how concerns about climate change are shaping the conservation policy landscape – in terms of the knowledge and rationales used as inputs, networks of actors involved, objectives sought, and actions proposed. We find that debates at the intersection of climate and biodiversity were overwhelmingly framed in relation to, or through the lens of carbon. Through a discussion of four core Climate-Motivated Responses, we illustrate how “carbon-logic”, and the initiatives that it generates, simultaneously creates threats to the objectives sought by some actors, and opportunities for the objectives sought by others. We situate our observations in the context of some of the historical dilemmas that have faced conservation, and discuss this current moment in the dynamic trajectory of conservation governance: a moment when decisions about conserving biodiversity are becoming entangled with carbon-logic and the market. In this case, while some actors seek opportunities for biodiversity ends by riding the coattails of the climate agenda, the threats of doing so may undermine the biological and social objectives of the CBD convention itself.  相似文献   

Amazonian magnetostratigraphy: Dating the first pulse of the Great American Faunal Interchange     

Kenneth E. Campbell  Donald R. Prothero  Lidia Romero-Pittman  Fritz Hertel  Nadia Rivera 《Journal of South American Earth Sciences》2010,29(3):619-626

The chronostratigraphy of the youngest Neogene deposits of the Amazon Basin, which comprise the Madre de Dios Formation in eastern Peru, remains unresolved. Although ⁴⁰Ar/³⁹Ar dates on two volcanic ashes from this formation in Peru provide critical baseline data points, stratigraphic correlations among scattered riverine outcrops in adjacent drainage basins remain problematic. To refine the chronostratigraphy of the Madre de Dios Formation, we report here the magnetostratigraphy of an outcrop on the Madre de Dios River in southeastern Peru. A total of 18 polarity zones was obtained in the ～65-m-thick Cerro Colorado section, which we correlate to magnetozones Chrons C4Ar to C2An (9.5–3.0 Ma) based on the prior ⁴⁰Ar/³⁹Ar dates. These results confirm the late Miocene age of a gomphothere recovered from the Ipururo Formation, which underlies the late Miocene Ucayali Unconformity at the base of the Cerro Colorado outcrop. The results also support earlier interpretations of a late Miocene age for other fossils of North American mammals recovered from basal conglomeratic deposits of the Madre de Dios Formation immediately above the Ucayali Unconformity. These mammals include other gomphotheres, peccaries, and tapirs, and their presence in South America in the late Miocene is recognized as part of the first pulse of the Great American Faunal Interchange.  相似文献   

On the effect of the martian crustal magnetic field on atmospheric erosion     

Xiaohua Fang  Michael W. Liemohn  Janet G. Luhmann 《Icarus》2010,206(1):130-138

Without the shielding of a strong intrinsic magnetic field, the martian atmosphere directly interacts with the impacting solar wind. The neutral constituents of the atmospheric corona can be ionized, and then picked up and accelerated by the magnetic field and convection electric field in the solar wind. A significant fraction of pickup ions escape Mars’ gravitational pull and are lost to space. This non-thermal escape process of heavy species is an important mechanism responsible for atmospheric erosion. While there is a perception that the martian magnetic anomalies are significant for the ionospheric density distribution and the bow shock standoff location, little is known about the quantitative influence of the martian crustal magnetic field on the global distribution of escaping pickup ions. In this paper, we apply a newly developed Monte Carlo ion transport model to resolve the crustal field effect on the pickup oxygen ion distribution around Mars. The background magnetic and electric fields, in which test particles are followed, are calculated using an independent three-dimensional multispecies MHD model. The effects of the crustal magnetic field on particle escape are quantified by varying the crustal field orientation in the model setup and comparing the corresponding test particle simulation results. The comparison is made by turning on or off the crustal field or changing the local time of the strongest field from the dayside to the dawnside. It is found that without the protection of the crustal magnetic field, the total amount of atmospheric escape through the tail region would be enhanced by more than a factor of two. It is shown that the crustal magnetic field not only regionally deflects the solar wind around the martian atmosphere, but also has an important global effect on atmospheric erosion and thus on long-term atmospheric evolution.  相似文献   

Radar absorption due to a corotating interaction region encounter with Mars detected by MARSIS     

David D. Morgan  Donald A. Gurnett  J. David Winningham  David A. Brain  Janet G. Luhmann  Jared R. Espley  Jeffrey J. Plaut 《Icarus》2010,206(1):95-103

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) is a subsurface and topside ionosphere radar sounder aboard the European Space Agency spacecraft Mars Express, in orbit at Mars since 25 December 2003, and in operation since 17 June 2005. The ionospheric sounding mode of MARSIS is capable of detecting the reflection of the sounding wave from the martian surface. This ability has been used in previous work to show that the surface reflection is absorbed and disappears during periods when high fluxes of energetic particles are incident on the ionosphere of Mars. These absorption events are believed to be the result of increased collisional damping of the sounding wave, caused by increased electron density below the spacecraft, in turn caused by impact ionization from the impinging particles. In this work we identify two absorption events that were isolated during periods when the surface reflection is consistently visible and when Mars is nearly at opposition. The visibility of the surface reflection is viewed in conjunction with particle and photon measurements taken at both Mars and Earth. Both absorption events are found to coincide with Earth passing through solar wind speed and ion flux signatures indicative of a corotating interaction region (CIR). The two events are separated by an interval of approximately 27 days, corresponding to one solar rotation. The first of the two events coincides with abruptly enhanced particle fluxes seen in situ at Mars. Simultaneous with the particle enhancement there are an abrupt decrease in the intensity of electron oscillations, typically seen by the Mars Express particle instrument ASPERA-3 between the magnetic pileup boundary and the martian bow shock, and a sharp drop in the solar wind pressure, seen in the proxy quantity based on MGS magnetometer observations. The decrease in oscillation intensity is therefore the probable effect of a relaxation of the martian bow shock. The second absorption event does not show a particle enhancement and complete ASPERA-3 data during that time are unavailable. Other absorption events are the apparent result of solar X-ray and XUV enhancements. We conclude that surface reflection absorption events are sometimes caused by enhanced ionospheric ionization from high energy particles accelerated by the shocks associated with a CIR. A full statistical analysis of CIRs in relation to observed absorption events in conjunction with a quantitative analysis of the deposition of ionization during space weather events is needed for a complete understanding of this phenomenon. If such analyses can be carried out, radar sensing of the martian ionosphere might be useful as a space weather probe.  相似文献