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51.
The Urban Heat Island Effect at Fairbanks, Alaska 总被引:13,自引:0,他引:13
Summary Using climatic data from Fairbanks and rurally situated Eielson Air Force Base in Interior Alaska, the growth of the Fairbanks
heat island was studied for the time period 1949 – 1997. The climate records were examined to distinguish between a general
warming trend and the changes due to an increasing heat island effect. Over the 49-year period, the population of Fairbanks
grew by more than 500%, while the population of Eielson remained relatively constant. The mean annual heat island observed
at the Fairbanks International Airport grew by 0.4 °C, with the winter months experiencing a more significant increase of
1.0 °C. Primary focus was directed toward long-term heat island characterization based on season, wind speed, cloud cover,
and time of day. In all cases, the minima temperatures were affected more than maxima and periods of calm or low wind speeds,
clear winter sky conditions, and nighttime exhibited the largest heat island effects.
Received August 17, 1998 Revised March 26, 1999 相似文献
52.
Jean-Claude Vannay Zachary D. Sharp Bernhard Grasemann 《Contributions to Mineralogy and Petrology》1999,137(1-2):90-101
Inverted metamorphic field gradients are preserved in two amphibolite facies metapelitic sequences forming the crystalline
core zone of the Himalayan orogen in the Sutlej valley (NW India). In the High Himalayan Crystalline Sequence (HHCS), metamorphic
conditions increase upwards from the staurolite zone at the base, through the kyanite-in and sillimanite-in isograds, finally
to reach partial melting conditions at the top. The structurally lower Lesser Himalayan Crystalline Sequence (LHCS) shows
a gradual superposition of garnet-in, staurolite-in and kyanite + sillimanite-in isograds. Although phase equilibria constraints
imply inverted temperature field gradients in both units, garnet-biotite (GARB) rim thermometry indicates final equilibration
at a nearly uniform temperature around T ≈ 600 °C across these sequences. The P-T path and garnet zoning data show that this apparent lack of thermal field gradient is mainly the consequence of a resetting
of the GARB equilibria during cooling. In order to constrain peak temperature conditions, 20 samples along the studied section
have been analysed for oxygen isotope thermometry. The isotopic fractionations recorded by quartz-garnet and quartz-aluminosilicate
mineral pairs indicate temperatures consistent with phase equilibria and P-T path constraints for metamorphic peak conditions. Together with barometry results, based on net transfer continuous reactions,
the oxygen isotope thermometry indicates peak conditions characterized by: (1) a temperature increase from T ≈ 570 to 750 °C at a nearly constant pressure around P ≈ 800 MPa, from the base to the top of the HHCS unit; (2) a temperature increase from T ≈ 610 to 700 °C and a pressure decrease from P ≈ 900 to 700 MPa, from the base to the top of the LHCS metapelites. Oxygen isotope thermometry thus provides the first quantitative
data demonstrating that the Himalayan inverted metamorphism can be associated with a complete inversion of the thermal field
gradient across the crystalline core zone of this orogen.
Received: 1 April 1999 / Accepted: 12 July 1999 相似文献
53.
Zachary K. Curtis Hua-sheng Liao Shu-Guang Li Prasanna Venkatesh Sampath David P. Lusch 《Ground water》2019,57(5):784-806
Managing nonpoint-source (NPS) pollution of groundwater systems is a significant challenge because of the heterogeneous nature of the subsurface, high costs of data collection, and the multitude of scales involved. In this study, we assessed a particularly complex NPS groundwater pollution problem in Michigan, namely, the salinization of shallow aquifer systems due to natural upwelling of deep brines. We applied a system-based approach to characterize, across multiple scales, the integrated groundwater quantity–quality dynamics associated with the brine upwelling process, assimilating a variety of modeling tools and data—including statewide water well datasets scarcely used for larger scientific analysis. Specifically, we combined (1) data-driven modeling of massive amounts of groundwater/geologic information across multiple spatial scales with (2) detailed analysis of groundwater salinity dynamics and process-based flow modeling at local scales. Statewide “hotspots” were delineated and county-level severity rankings were developed based on dissolved chloride (Cl−) concentration percentiles. Within local hotspots, the relative impact of upwelling was determined to be controlled by: (1) streams—which act as “natural pumps” that bring deeper (more mineralized) groundwater to the surface; (2) the occurrence of nearly impervious geologic material at the surface—which restricts fresh water dilution of deeper, saline groundwater; and (3) the space–time evolution of water well withdrawals—which induces slow migration of saline groundwater from its natural course. This multiscale, data-intensive approach significantly improved our understanding of the brine upwelling processes in Michigan, and has applicability elsewhere given the growing availability of statewide water well databases. 相似文献
54.
Characterizing the degree of amplitude‐variation‐with‐offset nonlinearity in seismic physical modelling reflection data
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The nonlinearity of the seismic amplitude‐variation‐with‐offset response is investigated with physical modelling data. Nonlinearity in amplitude‐variation‐with‐offset becomes important in the presence of large relative changes in acoustic and elastic medium properties. A procedure for pre‐processing physical modelling reflection data is enacted on the reflection from a water‐plexiglas boundary. The resulting picked and processed amplitudes are compared with the exact solutions of the plane‐wave Zoeppritz equations, as well as approximations that are first, second, and third order in , , and . In the low angle range of 0°–20°, the third‐order plane‐wave approximation is sufficient to capture the nonlinearity of the amplitude‐variation‐with‐offset response of a liquid‐solid boundary with , , and ρ contrasts of 1485–2745 m/s, 0–1380 m/s, and 1.00–1.19 gm/cc respectively, to an accuracy value of roughly 1%. This is in contrast to the linear Aki–Richards approximation, which is in error by as much as 25% in the same angle range. Even‐order nonlinear corrective terms are observed to be primarily involved in correcting the angle dependence of , whereas the odd‐order nonlinear terms are involved in determining the absolute amplitude‐variation‐with‐offset magnitudes. 相似文献
55.
56.
AbstractQuality is key to ensuring that the potential offered by weather radar networks is realized. To achieve optimum quality, a comprehensive radar data quality management system, designed to monitor the end-to-end radar data processing chain and evaluate product quality, is being developed at the UK Met Office. Three contrasting elements of this system are described: monitoring of key radar hardware performance indicators; generation of long-term integrations of radar products; and monitoring of radar reflectivity factor using synthesized observations from numerical weather prediction model fields. Examples of each component are presented and ways in which the different types of monitoring information have been used to both identify issues with the radar product data quality and help formulate solutions are given.
Editor Z.W. Kundzewicz; Guest editor R.J. MooreCitation Harrison, D., Georgiou, S., Gaussiat, N., and Curtis, A., 2013. Long-term diagnostics of precipitation estimates and the development of radar hardware monitoring within a radar product data quality management system. Hydrological Sciences Journal, 59 (7), 1327–1342. http://dx.doi.org/10.1080/02626667.2013.841316 相似文献
57.
Using the Climate Forecast System Reanalysis as weather input data for watershed models 总被引:4,自引:0,他引:4
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Daniel R. Fuka M. Todd Walter Charlotte MacAlister Arthur T. Degaetano Tammo S. Steenhuis Zachary M. Easton 《水文研究》2014,28(22):5613-5623
Obtaining representative meteorological data for watershed‐scale hydrological modelling can be difficult and time consuming. Land‐based weather stations do not always adequately represent the weather occurring over a watershed, because they can be far from the watershed of interest and can have gaps in their data series, or recent data are not available. This study presents a method for using the Climate Forecast System Reanalysis (CFSR) global meteorological dataset to obtain historical weather data and demonstrates the application to modelling five watersheds representing different hydroclimate regimes. CFSR data are available globally for each hour since 1979 at a 38‐km resolution. Results show that utilizing the CFSR precipitation and temperature data to force a watershed model provides stream discharge simulations that are as good as or better than models forced using traditional weather gauging stations, especially when stations are more than 10 km from the watershed. These results further demonstrate that adding CFSR data to the suite of watershed modelling tools provides new opportunities for meeting the challenges of modelling un‐gauged watersheds and advancing real‐time hydrological modelling. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
58.
59.
Dynamics of a fringe mangrove forest detected by Landsat images in the Mekong River Delta,Vietnam
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William Nardin Silvia Locatelli Valerie Pasquarella Maria Cristina Rulli Curtis E. Woodcock Sergio Fagherazzi 《地球表面变化过程与地形》2016,41(14):2024-2037
Mangrove forests dominate many tropical coastlines and are one of the most bio‐diverse and productive environments on Earth. However, little is known of the large‐scale dynamics of mangrove canopies and how they colonize intertidal areas. Here we focus on a fringe mangrove forest located in the Mekong River Delta, Vietnam; a fast prograding shoreline where mangroves are encroaching tidal flats. The spatial and temporal evolution of the mangrove canopy is studied using a time series of Landsat images spanning two decades as well as Shuttle Radar Topography Mission (SRTM) elevation data. Our results show that fast mangrove expansion is followed by an increase in Normalized Difference Vegetation Index (NDVI) in the newly established canopy. We observe three different dynamics of the mangrove fringe: in the southwest part of the fringe, near a deltaic distributary where the fringe boundary is linear, the canopy expands uniformly on the tidal flats with a high colonization rate and high NDVI values. In the northeast part of the fringe, near another distributary, the canopy expands at a much lower rate with low NDVI values. In the fringe center, far from the river mouths, the fringe boundary is highly irregular and mangroves expansion in characterized by sparse vegetated patches displaying low NDVI values. We ascribe these different dynamics to wave action and southwest longshore transport triggered by energetic northeasterly monsoons during winter. We further link the large‐scale dynamics of the fringe to small‐scale physical disturbances (waves, erosion and deposition) that might prevent the establishment of mangrove seedlings. Based on these results, we include mangrove encroachment in an already published conceptual model of progradation of the Mekong River Delta. We conclude that high NDVI values and a constantly linear vegetation–water interface are indicative of stable mangrove canopies undergoing fast expansion, probably triggered by sediment availability at the shore. Our results can be applied more generally to mangrove forests growing in minerogenic and high tidal range environments with high sediment inputs. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
60.
Heather Nicolson Andrew Curtis Brian Baptie Erica Galetti 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(1):74-86
Traditional methods of imaging the Earth's subsurface using seismic waves require an identifiable, impulsive source of seismic energy, for example an earthquake or explosive source. Naturally occurring, ambient seismic waves form an ever-present source of energy that is conventionally regarded as unusable since it is not impulsive. As such it is generally removed from seismic data and subsequent analysis. A new method known as seismic interferometry can be used to extract useful information about the Earth's subsurface from the ambient noise wavefield. Consequently, seismic interferometry is an important new tool for exploring areas which are otherwise seismically quiescent, such as the British Isles in which there are relatively few strong earthquakes. One of the possible applications of seismic interferometry is ambient noise tomography (ANT). ANT is a way of using interferometry to image subsurface seismic velocity variations using seismic (surface) waves extracted from the background ambient vibrations of the Earth. To date, ANT has been used successfully to image the Earth's crust and upper-mantle on regional and continental scales in many locations and has the power to resolve major geological features such as sedimentary basins and igneous and metamorphic cores. Here we provide a review of seismic interferometry and ANT, and show that the seismic interferometry method works well within the British Isles. We illustrate the usefulness of the method in seismically quiescent areas by presenting the first surface wave group velocity maps of the Scottish Highlands using only ambient seismic noise. These maps show low velocity anomalies in sedimentary basins such as the Moray Firth, and high velocity anomalies in igneous and metamorphic centres such as the Lewisian complex. They also suggest that the Moho shallows from south to north across Scotland which agrees with previous geophysical studies in the region. 相似文献