Field measurements of the flux and speed of wind-blown sand   总被引：13，自引：0，他引：13  

RONALD GREELEY  DAN G. BLUMBERG  STEVEN H. WILLIAMS 《Sedimentology》1996,43(1):41-52

A field experiment was conducted to measure the flux and speed of wind-blown sand under known conditions in a natural setting. The experiment, run at Pismo Beach, California, involved a tract 100 m long (parallel with the wind) by 20 m wide. The site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary-layer, temperature probes to determine atmospheric stability and wind vanes to determine wind direction. From these measurements, wind friction speeds were derived for each experimental run. In order to measure sand saltation flux, a trench 3 m long by 10 m wide (transverse to the wind direction) by 0·5 m deep was placed at the downwind end of the tract and lined with 168 collector bins, forming an ‘egg-box’ pattern. The mass of particles collected in each bin was determined for four experimental runs. In order to assess various sand-trap systems used in previous experiments, 12 Leatherman traps, one Fryberger trap and one array of Ames traps were deployed to collect particles concurrently with the trench collection. Particle velocities were determined from analysis of high-speed (3000 and 5000 frames per second) motion pictures and from a particle velocimeter. Sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined. Fluxes for each run were calculated using various previously published expressions, and then compared with the flux derived from the trench collection. Results show that Bagnold's (1941) model and White's (1979) equation most closely agree with values derived from the trench. Comparison of the various collector systems shows that the Leatherman and Ames traps most closely agree with the flux derived from the trench, although these systems tended to under-collect particles. Particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories. Results show that particle velocities from the velocimeter are in the range 0·5–7·0 m s^?1, compared to a wind friction velocity of 0·32–0·43 m s^?1 and a wind velocity of 2·7–3·9 m s^?1 at the height of the particle measurements. Descending particles tended to exceed the speeds of ascending particles by ～ 0·5 m s^?1.  相似文献   

Stagnation points and bifurcation in 3-D mountain airflow   总被引：1，自引：0，他引：1  

RONALD B. SMITH  SIGBJØRN GRØNÅS 《地球，A辑:动力气象学与海洋学》1993,45(1):28-43

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GEOGRAPHERS AND THE TENNESSEE VALLEY AUTHORITY*     

RONALD REED BOYCE 《Geographical review》2004,94(1):23-42

ABSTRACT. The Tennessee Valley Authority (TVA) was the largest, most comprehensive, and most controversial regional development and planning project in U.S. history. Geographers were involved from its inception and made impressive contributions. Aside from the unit area method of data gathering and mapping, little is known about their contributions, some of which were truly ahead of their time. Although their work and recommendations were often discarded and unheeded because of political turbulence, the geographers rarely complained or entered into the political arena. Their work in the TVA has generally gone unheralded and even unappreciated within the geography profession. The primary purpose of this article is to document their contributions.  相似文献   

Facies model for sedimentation in the glaciolacustrine environment     

RONALD W. MAY 《Boreas: An International Journal of Quaternary Research》1977,6(2):175-180

Diamictons which have characteristics of both basal tills and lacustrine sedimenis have been called by various authors waterlaid tills, lacuatrotills, subaqueous tills, aqualills, underwater tills, and other terms with the word till replaced by moraine. It is proposed that a more restrictive definition of these terms be applied based on criteria indicative of the environment of deposition.
The term lacustrotill is proposed for the till-like sediments deposited in the lacustrine environment by flow mechanisms. Their clasts are often striated and may exhibit preferred orientation unrelated to glacier movement. Deformation structures suggestive of slumping or flowage during deposition are usually present.
The term waterlaid till is proposed for sediments deposited beneath a floating glacier, where the water depth does not allow appreciable size separation during settling: glacial drift dumped in standing water at the snout of a glacier grounded on a lake bottom: or till deposited during re advances (perhaps annually) into a lake basin and subsequently slightly reworked by lacustrine processes.
These sediments contain glacially abraded clasts which may even show a weak preferred orientation related to glacial movement; deformation and flow structures will not normally be present: and they may he massive, or exhibit crude stratification.  相似文献   

The rôle of thermohaline circulation in climate     

SYUKURO MANABE    RONALD J. STOUFFER 《地球，A辑:动力气象学与海洋学》1999,51(1):91-109

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River‐dominated,shelf‐edge deltas: delivery of sand across the shelf break in the absence of slope incision     

JOSHUA F DIXON  RONALD J STEEL  CORNEL OLARIU 《Sedimentology》2012,59(4):1133-1157

Shelf‐edge deltas record the potential magnitude of sediment delivery from shallow water shelf into deep water slope and basin floor and, if un‐incised, represent the main increment of shelf‐margin growth into the basin, for that period. The three‐dimensional complexity of shelf‐edge delta systems and along‐strike variability at the shelf edge in particular, remains understudied. The Permian–Triassic Kookfontein Formation of the Tanqua Karoo Basin, South Africa, offers extensive three‐dimensional exposure (>100 km²) and therefore a unique opportunity to evaluate shelf‐edge strata from an outcrop perspective. Analysis of stratal geometry and facies distribution from 52 measured and correlated stratigraphic sections show the following: (i) In outer‐shelf areas, parasequences are characterized by undeformed, river‐dominated, storm‐wave influenced delta mouth‐bar sandstones interbedded with packages showing evidence of syn‐depositional deformation. The amount and intensity of soft‐sediment deformation increases significantly towards the shelf edge where slump units and debris flows sourced from collapsed mouth‐bar packages transport material down slope. (ii) On the upper slope, mouth‐bar and delta‐front sandstones pinch out within 2 km of the shelf break and most slump and debris flow units pinch out within 4 km of the shelf break. (iii) Further down the slope, parasequences consist of finer‐grained turbidites, characterized by interbedded, thin tabular siltstones and sandstones. The results highlight that river‐dominated, shelf‐edge deltas transport large volumes of sand to the upper slope, even when major shelf‐edge incisions are absent. In this case, transport to the upper slope through slumping, debris flows and un‐channellized low density turbidites is distributed evenly along strike.  相似文献