Above‐stream microclimate and stream surface energy exchanges in a wildfire‐disturbed riparian zone     

J. A. Leach  R. D. Moore 《水文研究》2010,24(17):2369-2381

Stream temperature and riparian microclimate were characterized for a 1·5 km wildfire‐disturbed reach of Fishtrap Creek, located north of Kamloops, British Columbia. A deterministic net radiation model was developed using hemispherical canopy images coupled with on‐site microclimate measurements. Modelled net radiation agreed reasonably with measured net radiation. Air temperature and humidity measured at two locations above the stream, separated by 900 m, were generally similar, whereas wind speed was poorly correlated between the two sites. Modelled net radiation varied considerably along the reach, and measurements at a single location did not provide a reliable estimate of the modelled reach average. During summer, net radiation dominated the surface heat exchanges, particularly because the sensible and latent heat fluxes were normally of opposite sign and thus tended to cancel each other. All surface heat fluxes shifted to negative values in autumn and were of similar magnitude through winter. In March, net radiation became positive, but heat gains were cancelled by sensible and latent heat fluxes, which remained negative. A modelling exercise using three canopy cover scenarios (current, simulated pre‐wildfire and simulated complete vegetation removal) showed that net radiation under the standing dead trees was double that modelled for the pre‐fire canopy cover. However, post‐disturbance standing dead trees reduce daytime net radiation reaching the stream surface by one‐third compared with complete vegetation removal. The results of this study have highlighted the need to account for reach‐scale spatial variability of energy exchange processes, especially net radiation, when modelling stream energy budgets. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Properties of electrostatic aggregates and their possible presence on Mars     

David Krinsley  Rodman Leach 《Precambrian Research》1981,14(2):167-178

Experiments indicate that at the high wind velocities characteristic of portions of the Martian surface, sand-sized particles will break down to silt and clay, which will then inevitably form sand-sized aggregates. Basalt and olivine aggregates held together by electrostatics were produced in an eolian abrasion device and their mass properties studied. It was difficult to examine aggregates after formation, as they separate and reform with very little handling, since electrostatic binding forces are quite weak.It is shown that aggregates range from 60 to more than 600 μm in diameter, that they generally are spheroidal in shape and become more elongate with increasing size, and that they tend to be layered with the inner portions more tightly bound than outer layers. After about one-and-one-half years, some aggregates lose their charge which is replaced with moisture; the aggregates retain their original sizes and shapes. None of the properties of electrostatic aggregates so far investigated are incompatible with the presence of these materials on Mars.  相似文献   

The relationships between tropical Atlantic sea level variability and major climate indices     

Jennifer A. M. Andrew  Harry Leach  Philip L. Woodworth 《Ocean Dynamics》2006,56(5-6):452-463

Relationships were examined between variability in tropical Atlantic sea level and major climate indices with the use of TOPEX/POSEIDON altimeter and island tide gauge data with the aim of learning more about the external influences on the variability of the tropical Atlantic ocean. Possible important connections were found between indices related to the El Niño–Southern Oscillation (ENSO) and the sea levels in all three tropical regions (north, equatorial, and south), although the existence of only one major ENSO event within the decade of available altimetry means that a more complete investigation of the ENSO-dependence of Atlantic sea level changes has to await for the compilation of longer data sets. An additional link was found with the Indian Ocean Dipole (IOD) in the equatorial region, this perhaps surprising observation is probably an artifact of the similarity between IOD and ENSO time series in the 1990s. No evidence was obtained for significant correlations between tropical Atlantic sea level and North Atlantic Oscillation or Antarctic Oscillation Index. The most intriguing relationship observed was between the Quasi-Biennial Oscillation and sea level in a band centered approximately on 10°S. A plausible explanation for the relationship is lacking, but possibilities for further research are suggested.  相似文献   

The origin and distribution of the loess in the Danube basin and associated regions of East-Central Europe — A review     

I.J. Smalley  J.A. Leach 《Sedimentary Geology》1978,21(1):1-26

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Correlation of hard X-ray and type III bursts in solar flares     

Vahé Petrosian  John Leach 《Solar physics》1983,87(1):165-175

The observed correlations between X-ray and type III radio emissions from solar bursts are described by means of a bivariate distribution function. Procedures for determining the form of this distribution are described using a sample of data analyzed by Kane (1981). With the help of this distribution a model is constructed to explain the correlation between the X-ray spectral index and the ratio of X-ray to radio intensities. Implications of the model are discussed.  相似文献   

Windblown sand on Venus: Preliminary results of laboratory simulations     

R. Greeley  J. Iversen  R. Leach  J. Marshall  B. White  S. Williams 《Icarus》1984,57(1):112-124

Small particles and winds of sufficient strength to move them have been detected from Venera and Pioneer-Venus data and suggest the existence of aeolian processes on Venus. The Venus wind tunnel (VWT) was fabricated in order to investigate the behavior of windblown particles in a simulated Venusian environment. Preliminary results show that sand-size material is readily entrained at the wind speeds detected on Venus and that saltating grains achieve velocities closely matching those of the wind. Measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from Martian and terrestial simulations. Results are in general agreement with theory, although certain discrepancies are apparent which may be attributed to experimental and/or theoretical-modeling procedures. Present findings enable a better understanding of Venusian surface processes and suggest that aeolian processes are important in the geological evolution of Venus.  相似文献   

Travel times for snowmelt-dominated headwater catchments: Influences of wetlands and forest harvesting,and linkages to stream water quality     

Jason A. Leach  James M. Buttle  Kara L. Webster  Paul W. Hazlett  Dean S. Jeffries 《水文研究》2020,34(10):2154-2175

The time it takes water to travel through a catchment, from when it enters as rain and snow to when it leaves as streamflow, may influence stream water quality and catchment sensitivity to environmental change. Most studies that estimate travel times do so for only a few, often rain-dominated, catchments in a region and use relatively short data records (<10 years). A better understanding of how catchment travel times vary across a landscape may help diagnose inter-catchment differences in water quality and response to environmental change. We used comprehensive and long-term observations from the Turkey Lakes Watershed Study in central Ontario to estimate water travel times for 12 snowmelt-dominated headwater catchments, three of which were impacted by forest harvesting. Chloride, a commonly used water tracer, was measured in streams, rain, snowfall and as dry atmospheric deposition over a 31 year period. These data were used with a lumped convolution integral approach to estimate mean water travel times. We explored relationships between travel times and catchment characteristics such as catchment area, slope angle, flowpath length, runoff ratio and wetland coverage, as well as the impact of harvesting. Travel time estimates were then used to compare differences in stream water quality between catchments. Our results show that mean travel times can be variable for small geographic areas and are related to catchment characteristics, in particular flowpath length and wetland cover. In addition, forest harvesting appeared to decrease mean travel times. Estimated mean travel times had complex relationships with water quality patterns. Results suggest that biogeochemical processes, particularly those present in wetlands, may have a greater influence on water quality than catchment travel times.  相似文献   

Excursion to the North Downs in Kent: Saturday,July 17th, 1920     

Arthur L. Leach  M.J. Bassett 《Proceedings of the Geologists' Association. Geologists' Association》1921,32(1):36-IN1

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Excursion to the West Wickham Bourne,Hayes and Keston Commons: Saturday,July 19th, 1919     

A.L. Leach 《Proceedings of the Geologists' Association. Geologists' Association》1919,30(3):150-152

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Report of the session, 1916–17     

A.L. Leach 《Proceedings of the Geologists' Association. Geologists' Association》1917,28(2):105-106

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