Simplification and Validation of a Spectral-Tensor Model for Turbulence Including Atmospheric Stability   总被引：1，自引：1，他引：0  

Abhijit Chougule  Jakob Mann  Mark Kelly  Gunner C. Larsen 《Boundary-Layer Meteorology》2018,167(3):371-397

A spectral-tensor model of non-neutral, atmospheric-boundary-layer turbulence is evaluated using Eulerian statistics from single-point measurements of the wind speed and temperature at heights up to 100 m, assuming constant vertical gradients of mean wind speed and temperature. The model has been previously described in terms of the dissipation rate \(\epsilon \), the length scale of energy-containing eddies \(\mathcal {L}\), a turbulence anisotropy parameter \(\varGamma \), the Richardson number Ri, and the normalized rate of destruction of temperature variance \(\eta _\theta \equiv \epsilon _\theta /\epsilon \). Here, the latter two parameters are collapsed into a single atmospheric stability parameter z / L using Monin–Obukhov similarity theory, where z is the height above the Earth’s surface, and L is the Obukhov length corresponding to \(\{Ri,\eta _\theta \}\). Model outputs of the one-dimensional velocity spectra, as well as cospectra of the streamwise and/or vertical velocity components, and/or temperature, and cross-spectra for the spatial separation of all three velocity components and temperature, are compared with measurements. As a function of the four model parameters, spectra and cospectra are reproduced quite well, but horizontal temperature fluxes are slightly underestimated in stable conditions. In moderately unstable stratification, our model reproduces spectra only up to a scale \(\sim \) 1 km. The model also overestimates coherences for vertical separations, but is less severe in unstable than in stable cases.  相似文献   

Taming a “chaotic concept”: gentrification and segmented consumption in Brooklyn, 2002–2012     

Mike Owen Benediktsson  Brian Lamberta  Erika Larsen 《Urban geography》2016,37(4):590-610

Public debate and prior scholarship tend to emphasize the link between gentrification and high-end chain retail, underscoring the importance of taste cultures tied to social class in making sense of gentrification’s impact on neighborhood identity. In this study, we present evidence from 10 years of change in the businesses of Brooklyn, New York City, a period of extensive gentrification across a wide variety of neighborhood and census-tract level contexts. Adopting census tracts clustered in neighborhoods as the units of analysis, we model the effects of institutional and demographic change on two separate outcomes: chain retail density and homogeneity in the types of goods and services available. We argue that changes in consumer culture embedded in broader processes of gentrification are neither “chaotic” nor “unitary” but are “segmented” according to local spatial and demographic context, taking two discrete forms: institutionally facilitated corporatization; lifestyle-driven homogenization.  相似文献   

On the impact of wind on the development of wave field during storm Britta     

Xiaoli Guo Larsén  Jianting Du  Rodolfo Bolaños  Søren Larsen 《Ocean Dynamics》2017,67(11):1407-1427

The observation of extreme waves at FINO 1 during storm Britta on the 1st November 2006 has initiated a series of research studies regarding the mechanisms behind. The roles of stability and the presence of the open cell structures have been previously investigated but not conclusive. To improve our understanding of these processes, which are essential for a good forecast of similarly important events offshore, this study revisits the development of storm Britta using an atmospheric and wave coupled modeling system, wind and wave measurements from ten stations across the North Sea, cloud images and Synthetic Aperture Radar (SAR) data. It is found here that a standard state-of-the-art model is capable of capturing the important characteristics of a major storm like Britta, including the storm path, storm peak wind speed, the open cells, and peak significant wave height (H _s ) for open sea. It was also demonstrated that the impact of the open cells has negligible contribution to the development of extreme H _s observed at FINO 1. At the same time, stability alone is not sufficient in explaining the development of extreme H _s . The controlling conditions for the development of Britta extreme H _s observed at FINO 1 are the persistent strong winds and a long and undisturbed fetch over a long period.  相似文献   

Biotic drivers of river and floodplain geomorphology – New molecular methods for assessing present‐day and past biota          下载免费PDF全文

Annegret Larsen  Nadir Alvarez  Christoph Sperisen  Stuart N. Lane 《地球表面变化过程与地形》2018,43(1):333-338

Geomorphology has increasingly considered the role of biotic factors as controls upon geomorphic processes across a wide range of spatial and temporal scales. Where timescales are long (centennial and longer), it has been possible to quantify relationships between geomorphic processes and vegetation using, for example, the pollen record. However, where the biotic agents are fauna, longer term reconstruction of the impacts of biological activity upon geomorphic processes is more challenging. Here, we review the prospect of using environmental DNA as a molecular proxy to decipher the presence and nature of faunal influences on geomorphic processes in both present and ancient deposits. When used appropriately, this method has the potential to improve our understanding of biotic drivers of geomorphic processes, notably fauna, over long timescales and so to reconstruct how such drivers might explain the landscape as we see it today. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Slopewash,surface runoff and fine-litter transport in forest and landslide scars in humid-tropical steeplands,luquillo experimental forest,Puerto Rico     

Matthew C. Larsen  Angel J. Torres-Snchez  Iris M. Concepcin 《地球表面变化过程与地形》1999,24(6):481-502

Rainfall, slopewash (the erosion of soil particles), surface runoff and fine-litter transport steepland sites in the Luquillo Experimental Forest, Puerto Rico (18° 20’ N, 65° 45’ W) were measured from 1991 to 1995. Hillslopes underlain by (1) Cretaceous tuffaceous sandstone and silstone in subtropical rain (tanonuco) forest with vegetation recovering from Hurricane Hugo (1989), and (2) Tertiary quartz diorite in subtropical lower mantone wet (colorado and dwarf) forest with undisturbed forest canopy were compared to recent landslide scars. Monthly surface runoff on these very steep hillslopes (24° to 43°) was only 0·2 to 0·5 per cent of monthly rainfall. Slopewash was higher in sandy loam soils whose parent material is quartz diorite (averaging 46 g m⁻² a⁻¹) than in silty clay loam soils derived from tuffaceous sandstone and siltstone where the average was 9 g m⁻² a⁻¹. Annual slopewash of 100 to 349 g m⁻² on the surfaces of two recent, small landslide scars was measured initially but slopewash decreased to only 3 to 4 g m⁻² a⁻¹ by the end of the study. The mean annual mass of fine litter (mainly leaves and twigs) transported downslope at the forested sites ranged from 5 to 8 g m⁻² and was lower at the tabonuco forest site, where post-Hurricane Hugo recovery is still in progress. Mean annual fine-litter transport was 2·5 g m⁻² on the two landslide scars. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Measuring the benefits and costs of community education and outreach in marine protected areas     

Craig Leisher  Sangeeta Mangubhai  Sebastiaan Hess  Hesti Widodo  Tri Soekirman  Salomina Tjoe  Stevanus Wawiyai  S. Neil Larsen  Lukas Rumetna  A. Halim  M. Sanjayan 《Marine Policy》2012

Conservation organizations often invest considerable resources in education and outreach activities in and around marine protected areas (MPAs). The expectation is that such efforts will change local knowledge, attitudes and ultimately behavior. This is one of the first studies to assess the efficacy of using education and outreach activities to improve community knowledge and attitudes about an MPA. Random sample surveys in 2005 and 2010 (n=1213) before and after education and outreach activities are compared. Program budgets for the same period give the investment levels. With an investment level averaging US$24 per capita/year, the result was an average increase of 33% in “yes” responses across 15 indicators of knowledge and attitudes towards marine conservation. The increase in knowledge and positive attitudes was associated with a large decrease in “not sure” responses, suggesting that community members with fewer initial preconceptions are the most effective target for education and outreach activities. This study demonstrates that investments in MPA education and outreach can generate increases in local knowledge and positive attitudes, and changing knowledge and attitudes is expected to contribute to the long-term compliance with MPA regulations.  相似文献   

Water content and land use history controlling soil CO2 respiration and carbon stock in savanna soil and groundnut fields in semi-arid Senegal     

Bo Elberling  Rasmus Fensholt  L. Larsen  A-I. S. Petersen  Inge Sandholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):47-56

Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO₂ to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO₂ effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO₂ production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO₂ effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO₂ m^?2 s^?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO₂ production was simulated to be in the range of 31–38 mol C m^?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter.  相似文献   

The Influence of the “Mixed Pixel” Problem on the Detection of Analogous Forest Communities Between Presettlement and Present in Western New York∗     

Barry J. Kronenfeld  Yi-Chen Wang  Chris P. S. Larsen 《The Professional geographer》2013,65(2):182-196

We conducted a land change analysis to determine if the forest communities of presettlement and present contain areas that are analogous in composition, using surveys of the Holland Land Company (1797–1799) and U.S. Forest Service (1991–1993) from western New York. Gridded forest-type maps are produced from each survey using two models: a uniform model that assumes each data grid cell is occupied by a single forest type, and a mixture model in which grid cells are assumed to be occupied by multiple forest types in different proportions. The mixture model consistently detects a larger area of analogous communities in the two time periods at both global and local scales.  相似文献   

Community discourse and the emerging amenity landscapes of the rural American West     

Soren Larsen  Craig Hutton 《GeoJournal》2012,77(5):651-665

We explore the construction of community meaning on an emerging amenity landscape in the western United States through in-depth interviews and ethnographic fieldwork with residents of rural Fremont County, Colorado. The meanings ascribed to community center on different interpretations of home, social interaction, and personal identity. Although in some cases these differences correspond to the conventional division between new and long-term residents, the more significant finding was a discourse of “co-opetition” that captures a broader countywide understanding of community as simultaneous cooperation and competition among local stakeholders. Ultimately, this conceptualization of rural community is a way of negotiating the form and function of the amenity landscape. The production of meaningful social interaction points to opportunities for engaging residents in land management as they interact with one another and the landscape.  相似文献   

Governing resilience building in Thailand's tourism-dependent coastal communities: Conceptualising stakeholder agency in social-ecological systems     

Rasmus Klocker Larsen  Emma CalgaroFrank Thomalla 《Global Environmental Change》2011,21(2):481-491

In current scientific efforts to harness complementarity between resilience and vulnerability theory, one response is an ‘epistemological shift’ towards an evolutionary, learning based conception of the ‘systems-actor’ relation in social-ecological systems. In this paper, we contribute to this movement regarding the conception of stakeholder agency within social-ecological systems. We examine primary evidence from the governance of post-disaster recovery and disaster risk reduction efforts in Thailand's coastal tourism-dependent communities following the 2004 Indian Ocean Tsunami. Through an emerging storyline from stakeholders, we construct a new framework for conceptualising stakeholder agency in social-ecological systems, which positions the notion of resilience within a conception of governance as a negotiated normative process. We conclude that if resilience theory is proposed as the preferred approach by which disaster risk reduction is framed and implemented, it needs to acknowledge much more explicitly the role of stakeholder agency and the processes through which legitimate visions of resilience are generated.  相似文献