On the Determination of the Neutral Drag Coefficient in the Convective Boundary Layer   总被引：1，自引：1，他引：0  

A.A. Grachev  C.W. Fairall  S.E. Larsen 《Boundary-Layer Meteorology》1998,86(2):257-278

Based on the idea that free convection can be considered as a particular case of forced convection, where the gusts driven by the large-scale eddies are scaled with the Deardorff convective velocity scale, a new formulation for the neutral drag coefficient, C_Dn, in the convective boundary layer (CBL) is derived. It is shown that (i) a concept of C_Dn can still be used under strongly unstable conditions including a pure free-convection regime even when no logarithmic portion in the velocity profile exists; (ii) gustiness corrections must be applied for rational calculations of C_Dn; and (iii) the stratification function used in the derivation of C_Dn should satisfy the theoretical free-convection limit. The new formulation is compared with the traditional relationship for C_Dn, and data collected over the sea (during the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) and the San Clemente Ocean Probing Experiment (SCOPE)) and over land (during the BOREX-95 experiment) are used to illustrate the difference between the new and traditional formulations. Compared to the new approach, the traditional formulation strongly overestimates C_Dn and z_o in the CBL for mean wind speed less than about 2 m s^-1. The new approach also clarifies several contradictory results from earlier works. Some aspects related to an alternate definition of the neutral drag coefficient and the wind speed and the stress averaging procedure are considered.  相似文献   

Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz     

Erik Thorson Brown  Robert F. Stallard  Matthew C. Larsen  Didier L. Bourls  Grant M. Raisbeck  Franoise Yiou 《Earth and Planetary Science Letters》1998,160(3-4):723-728

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.  相似文献   

Ar/Ar geochronology of the West Greenland Tertiary volcanic province     

M. Storey  R. A. Duncan  A. K. Pedersen  L. M. Larsen  H. C. Larsen 《Earth and Planetary Science Letters》1998,160(3-4):569-586

Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A ⁴⁰Ar/³⁹Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that 80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60.5±0.4 Ma). Minimum estimates of magma production rates (1.3×10⁻⁴ km³ year⁻¹ km⁻¹) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to <0.7×10⁻⁴ km³ year⁻¹ km⁻¹ (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British–Irish province. This is interpreted as manifesting the impact and rapid (>1 m/year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at 62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at 55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.  相似文献   

The Persian gulf: holocene carbonate sedimentation and diagenesis in a shallow epicontinental sea: B.H. PURSER, ed. (1973): 471 pp. 250 figs. and folding maps. Berlin—Heidelberg—New York: Springer Verlag. DM 66,-, US$ 29.80     

Karl Butzer  Curtis Larsen 《Geoforum》1974,5(4):104

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Topographically moderated soil water seasons impact vegetation dynamics in semiarid mountain catchments: Illustrations from the Dry Creek Experimental Watershed,Idaho, USA     

Michael J. Poulos  Toni J. Smith  Shawn G. Benner  Jennifer L. Pierce  Alejandro N. Flores  Mark S. Seyfried  James P. McNamara 《水文研究》2021,35(12):e14421

Water stored in soils, in part, controls vegetation productivity and the duration of growing seasons in wildland ecosystems. Soil water is the dynamic product of precipitation, evapotranspiration and soil properties, all of which vary across complex terrain making it challenging to decipher the specific controls that soil water has on growing season dynamics. We assess how soil water use by plants varies across elevations and aspects in the Dry Creek Experimental Watershed in southwest Idaho, USA, a mountainous, semiarid catchment that spans low elevation rain to high elevation snow regimes. We compare trends in soil water and soil temperature with corresponding trends in insolation, precipitation and vegetation productivity, and we observe trends in the timing, rate and duration of soil water extraction by plants across ranges in elevation and aspect. The initiation of growth-supporting conditions, indicated by soil warming, occurs 58 days earlier at lower, compared with higher, elevations. However, growth-supporting conditions also end earlier at lower elevations due to the onset of soil water depletion 29 days earlier than at higher elevations. A corresponding shift in peak NDVI timing occurs 61 days earlier at lower elevations. Differences in timing also occur with aspect, with most threshold timings varying by 14–30 days for paired north- and south-facing sites at similar elevations. While net primary productivity nearly doubles at higher elevations, the duration of the warm-wet period of active water use does not vary systematically with elevation. Instead, the greater ecosystem productivity is related to increased soil water storage capacity, which supports faster soil water use and growth rates near the summer solstice and peak insolation. Larger soil water storage does not appear to extend the duration of the growing season, but rather supports higher growing season intensity when wet-warm soil conditions align with high insolation. These observations highlight the influence of soil water storage capacity in dictating ecological function in these semiarid steppe climatic regimes.  相似文献   

Industrial minerals and rocks, aggregates and natural stones in the Nordic countries     

Kurt Johansson Rune B. Larsen Markku J. Lehtinen Lars Persson Mika Raeisaenen Stig A. Schack Pedersen Paer Weihed Nils-Gunnar Wik 《《幕》》2008,31(1):133-139

The Nordic countries, including Greenland, have a long tradition in mining. The industrial minerals sector is expanding in most Nordic countries and extensive development has taken place during the last few years. The main commodities mined are carbonate rocks, quartz, feldspar, apatite, olivine and talc.
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies.  相似文献   

Microstructural evidence of low‐strain,time‐transgressive subglacial deformation     

N. K. Larsen  J. A. Piotrowski  J. Menzies 《第四纪科学杂志》2007,22(6):593-608

Microstructural analyses were used to investigate the formation of a macroscale‐massive till at Knud Strand in Denmark. More than 100 thin sections were examined and microstructures mapped and counted for quantitative comparison and interpretation. Microstructures indicative of both brittle (grain lineations, edge‐to‐edge crushed grains) and ductile (turbate structures) deformation are evenly distributed in vertical profiles through the till, suggesting that strain contributed to its formation. Discrete shears (grain lineations and plasmic fabric) probably accommodated most deformation, whereas rotational deformation was less prominent. The microshear geometry fits the predicted Coulomb–Mohr failure criterion, indicating that till behaves as a plastic material. Strain estimate of ca. 10¹ from micromorphological proxies is two–three orders of magnitude lower than expected if the till was subjected to pervasive deformation. A hybrid of lodgement and time‐transgressive deformation is envisaged as the till‐forming processes. Our data suggest that even abundant evidence of microscale deformation at continuing high levels of strain may only record the latest process of deposition and deformation and therefore not fully reflect the complexity of till genesis. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Glacial stratigraphy of East and Central Jutland     

Christian  Kronborg  Henry  Bender  Regnar  Bjerre  Rud  Friborg  Hans O.  Jacobsen  Lars  Kristiansen  Poul  Rasmussen  Poul R.  Sørensen Gunnar  Larsen 《Boreas: An International Journal of Quaternary Research》1990,19(3):273-287

Glaciostratigraphic investigations at one key locality (Haldum), 9 major and about 160 minor localities in East and Central Jutland, Denmark, together with laboratory work, have led to the establishment of a stratigraphy consisting of 10 till units, usually separated by meltwater deposits. The stratigraphy is in some degree supported by thermoluminescence datings. The complete sequence includes one till unit with associated meltwater deposits of Menapian age, three till units with intercalated meltwater deposits of Elsterian age, marine sediments deposited during the Holsteininan, and three till units with intercalated of Elsterian age, marine sediments deposited during the Holsteinian, and three till units with intercalated glaciofluvial sedimants of Saalian age. Eemian deposits are present above this level, and the whole sequence is capped by till and meltwater deposits related to three glacial advances during the Weichselian.  相似文献   

The Plio-Pleistocene glaciation of the Barents Sea–Svalbard region: a new model based on revised chronostratigraphy     

Jochen Knies  Jens Matthiessen  Christoph Vogt  Jan Sverre Laberg  Berit O. Hjelstuen  Morten Smelror  Eiliv Larsen  Karin Andreassen  Tor Eidvin  Tore O. Vorren 《Quaternary Science Reviews》2009,28(9-10):812-829

Based on a revised chronostratigraphy, and compilation of borehole data from the Barents Sea continental margin, a coherent glaciation model is proposed for the Barents Sea ice sheet over the past 3.5 million years (Ma). Three phases of ice growth are suggested: (1) The initial build-up phase, covering mountainous regions and reaching the coastline/shelf edge in the northern Barents Sea during short-term glacial intensification, is concomitant with the onset of the Northern Hemisphere Glaciation (3.6–2.4 Ma). (2) A transitional growth phase (2.4–1.0 Ma), during which the ice sheet expanded towards the southern Barents Sea and reached the northwestern Kara Sea. This is inferred from step-wise decrease of Siberian river-supplied smectite-rich sediments, likely caused by ice sheet blockade and possibly reduced sea ice formation in the Kara Sea as well as glacigenic wedge growth along the northwestern Barents Sea margin hampering entrainment and transport of sea ice sediments to the Arctic–Atlantic gateway. (3) Finally, large-scale glaciation in the Barents Sea occurred after 1 Ma with repeated advances to the shelf edge. The timing is inferred from ice grounding on the Yermak Plateau at about 0.95 Ma, and higher frequencies of gravity-driven mass movements along the western Barents Sea margin associated with expansive glacial growth.  相似文献   

Introduction to “tectonics and sedimentation of Southeast Asian continental margin and marginal seas”     

Zhen Sun  Chun-Feng Li  Guo-Liang Zhang  Hans Christian Larsen 《Marine Geophysical Researches》2015,36(2-3):99-100

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