Atmospheric dispersion in the arctic: Winter-time boundary-layer measurements     

Alex Guenther  Brian Lamb 《Boundary-Layer Meteorology》1989,49(4):339-366

The winter-time arctic atmospheric boundary layer was investigated with micrometeorological and SF₆ tracer measurements collected in Prudhoe Bay, Alaska. The flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. The relatively warm maritime air mass originating over the nearby, partially frozen Beaufort Sea is cooled at the tundra surface resulting in strong (4 to 30 °C · (100 m)^-1) temperature inversions with light winds and a persistent weak (1 to 2 °C · (100 m)^-1) surface inversion with wind speeds up to 17 m s^-1. The absence of any diurnal atmospheric stability pattern during the study was due to the very limited solar insolation. Vertical profiles were measured with a multi-level mast from 1 to 17 m and with a Doppler acoustic sounder from 60 to 450 m. With high wind speeds, stable layers below 17 m and above 300 m were typically separated by a layer of neutral stability. Turbulence statistics and spectra calculated at a height of 33 m are similar to measurements reported for non-arctic, open terrain sites and indicate that the production of turbulence is primarily due to wind shear. The distribution of wind direction recorded at 1 Hz was frequently non-Gaussian for 1-hr periods but was always Gaussian for 5-min periods. We also observed non-Gaussian hourly averaged crosswind concentration profiles and assume that they can be modeled by calculating sequential short-term concentrations, using the 5-min standard deviation of horizontal wind direction fluctuations () to estimate a horizontal dispersion coefficient ( _y ), and constructing hourly concentrations by averaging the short-term results. Non-Gaussian hourly crosswind distributions are not unique to the arctic and can be observed at most field sites. A weak correlation between horizontal ( _v ) and vertical ( _w ) turbulence observed for both 1-hr and 5-min periods indicates that a single stability classification method is not sufficient to determine both vertical and horizontal dispersion at this site. An estimate of the vertical dispersion coefficient, _z , could be based on or a stability classification parameter which includes vertical thermal and wind shear effects (e.g., Monin-Obukhov length, L).  相似文献   

Comment On: 'Early Silurian Palaeolatitude of the Springdale Group Redbeds of Central Newfoundland: A Palaeomagnetic Determination With A Remanence Anisotropy Test For Inclination Error' By J. P. Hodych and K. L. Buchan     

John Stamatakos  Rob Van Der  Voo  Ben Van Der  Pluijm  Stephen Potts  Trond Torsvik 《Geophysical Journal International》1994,119(3):1009-1013

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The effect of a finitely conducting layer in the mantle on magnetic instability in the core     

C. J. Lamb 《Geophysical Journal International》1995,121(3):763-774

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Comment On Two Recent Teleseismic Waveform Inversion Articles By Taymaz Et Al.     

Rob Westaway 《Geophysical Journal International》1993,112(3):538-542

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Slope-induced changes in channel character along a gravel-bed stream: The Allt Dubhaig,Scotland     

Rob Ferguson  Phil Ashworth 《地球表面变化过程与地形》1991,16(1):65-82

Changes in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to 0.00015 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near-braided, (2) meandering with active point-bar chutes, (3) meandering with active outer-bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical concepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope-induced changes in hydraulic properties.  相似文献   

Helmut Erich Landsberg, 1906–1985     

Hubert H. Lamb 《Climatic change》1986,9(3):265-266

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Effects of weathering on site response     

Rob Davis 《地震工程与结构动力学》1995,24(2):301-309

Nearly all studies of site response under seismic excitation employ idealized site models in which uniform layers of homogeneous soils are separated by perfect interfaces. The impedance mismatch at each interface gives rise to wave reflections which strongly affect the calculated free surface response. In reality, these perfect interfaces may often not exist. Instead, a zone in which materials from both above and below are mingled may form a blurred interface between layers. This article examines the effects of such weathered zones. The zone is modelled by a linearly varying shear modulus so that no abrupt impedance change occurs. Significant differences in response of weathered and unweathered profiles are found.  相似文献   

Geochemical studies in the drainage basin of the Rio Vouga,Portugal. IV. Impact of land use on the hydrogeochemistry of natural waters in the Vouzela region   总被引：1，自引：0，他引：1  

Rob N. J. Comans  Cornelis H. Van Der Weijden  Simon P. Vriend 《Environmental Geology》1987,9(2):119-128

A hydrogeochemical study of the impact of land use on the composition of natural waters in the Vouzela region in northern Portugal was carried out during the summer of 1983. Water samples were collected from spring and major streams in the area and analyzed for major constituents and some trace elements. Analysis of variance and subsequent pairwise contrast tests demonstrated that waters from agricultural areas are significantly enriched in constiluents such as Na, K, Ca, Mg, Sr, Cl, SO₄, and NO₃. High concentrations of these ions in agricultural areas are the result of both the application of fertilizers and enhanced evaporation by the intensive irrigation of agricultural lands. Constitutents such as H₄SiO₄, HCO₃, F, and probably Li, which are typically related to mineral weathering, were not affected by land use. In waters from forested areas the concentration of most constituents was about 20% higher than in waters from uncultivated areas with mainly a grass cover. This reflects the difference in the evapotranspiration of these two vegetation types. The chemistry of the Rio Zela clearly reflects differences in land use in the Rio Zela valley.  相似文献   

An experiment on reservoir representation schemes to improve hydrologic prediction: coupling the national water model with the HEC-ResSim     

Jungho Kim  Laura Read  Lynn E. Johnson  David Gochis  Rob Cifelli  Heechan Han 《水文科学杂志》2020,65(10):1652-1666

ABSTRACT

This study experiments with reservoir representation schemes to improve the ability to model active water management in the National Water Model (NWM). For this purpose, we developed an integrated water management model, NWM-ResSim, by coupling the NWM with HEC-ResSim, and two reservoir representation schemes are tested: simulation of reservoir operations and retrieval of scheduled operations. The experiments focus on a pilot reservoir domain in the Russian River basin – Lake Mendocino, California – and its contributing watershed. The evaluation results suggest that the NWM-ResSim improves the simulation performance of reservoir outflow from this managed reservoir over the NWM default level pool routing scheme. The degree of this improvement depends on the suitability of the operation guidance; the reservoir operations simulation scheme could have acceptable errors for the purposes of water resources management, but not for flood operations. Results of the retrieval scheme of scheduled operations demonstrated better performance for sub-daily flood operations.  相似文献   

Luminous and dark matter in the Milky Way     

Rob P. Olling  Michael R. Merrifield 《Monthly notices of the Royal Astronomical Society》2001,326(1):164-180

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