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Horizontal Scales (horizontal + scale)
Selected AbstractsForcing singular vectors and other sensitive model structuresTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 592 2003J. Barkmeijer Abstract Model tendency perturbations can, like analysis perturbations, be an effective way to influence forecasts. In this paper, optimal model tendency perturbations, or forcing singular vectors, are computed with diabatic linear and adjoint T42L40 versions of the European Centre for Medium-Range Weather Forecasts' forecast model. During the forecast time, the spatial pattern of the tendency perturbation does not vary and the response at optimization time (48 hours) is measured in terms of total energy. Their properties are compared with those of initial singular vectors, and differences, such as larger horizontal scale and location, are discussed. Sensitivity calculations are also performed, whereby a cost function measuring the 2-day forecast error is minimized by only allowing tendency perturbations. For a given number of minimization steps, this approach yields larger cost-function reductions than the sensitivity calculation using only analysis perturbations. Nonlinear forecasts using only one type of perturbation confirm an improved performance in the case of tendency perturbations. For a summer experiment a substantial reduction of the systematic error is shown in the case of forcing sensitivity. Copyright © 2003 Royal Meteorological Society. [source] Remote visualisation of Labrador convection in large oceanic datasetsATMOSPHERIC SCIENCE LETTERS, Issue 4 2005L. J. West Abstract The oceans relinquish O(1PW) of heat into the atmosphere at high latitudes, the lion's share of which originates in localised ,hotspots' of violent convective mixing, but despite their small horizontal scale,O(10,100km),these features may penetrate deeply into the thermocline and are vital in maintaining the Atlantic Meridional Overturning Circulation (MOC). Accurate modelling of the MOC, therefore, requires a large-scale numerical model with very fine resolution. The global high-resolution ocean model, Ocean Circulation Climate Advanced Model (OCCAM) has been developed and run at the Southampton Oceanography Centre (SOC) for many years. It was configured to resolve the energetic scales of oceanic motions, and its output is stored at the Manchester Supercomputer Centre. Although this community resource represents a treasure trove of potential new insights into the nature of the world ocean, it remains relatively unexploited for a number of reasons, not the least of which is its sheer size. A system being developed at SOC under the auspices of the Grid for Ocean Diagnostics, Interactive Visualisation and Analysis (GODIVA) project makes the remote visualisation of very large volumes of data on modest hardware (e.g. a laptop with no special graphics capability) a present reality. The GODIVA system is enabling the unresolved question of oceanic convection and its relationship to large-scale flows to be investigated; a question that lies at the heart of many current climate change issues. In this article, one aspect of the GODIVA is presented, and used to locate and visualise regions of convective mixing in the OCCAM Labrador Sea. Copyright © 2006 Royal Meteorological Society [source] The use of GIS-based digital morphometric techniques in the study of cockpit karstEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2007P. Lyew-Ayee Abstract Cockpit karst landscapes are among the most distinctive landscapes in the world, and have been the focus of long-standing scientific interest. Early researchers used largely descriptive techniques to categorize the terrain, and subsequent work has not attempted to critically re-evaluate descriptions of landscapes using more sophisticated methods. The distinctive surface topography of cockpit karst areas can be characterized in order to compare them with other karst as well as non-karst areas, and to determine geological and/or climatic conditions that are responsible for the observed terrain. Process models of the rate of karst denudation or evolution can only be accurate if the contemporary morphology of the landscape is quantitatively and unambiguously defined. A detailed analysis of cockpit karst terrain is carried out using the latest GIS-based digital morphometric techniques in order to assess the nature of such terrain and provide further information for subsequent modelling, as well as other non-geomorphological applications, such as environmental management and conservation issues. The paper presents the methodology used for the digital analysis of terrain and landforms in the distinctive Cockpit Country area of Jamaica and its environs. The results indicate that cockpit karst may be categorized based on its vertical, horizontal and shape characteristics, as well as by looking at the semivariogram, slope characteristics, and landscape relief scale, which combine measures of vertical and horizontal scales. Copyright © 2006 John Wiley & Sons, Ltd. [source] Scaling turbulent atmospheric stratification.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008I: Turbulence, waves Abstract In this first of a three-part series, we argue that the dynamics of turbulence in a stratified atmosphere should depend on the buoyancy over a wide range of vertical scales and on energy flux over a wide range of horizontal scales; it should be scaling, but anisotropic, not isotropic. We compare the leading statistical theories of atmospheric stratification which are conveniently distinguished by the elliptical dimension Ds which quantifies their degree of spatial stratification. This includes the mainstream isotropic 2-D (large scales), isotropic 3-D (small scales) theory but also the more recent linear gravity wave theories (Ds = 7/3) and the classical fractionally integrated flux (FIF) 23/9-D unified scaling model. In the latter, the horizontal wind has a k,5/3 spectrum as a function of horizontal wavenumber determined by the energy flux and a k,11/5 energy spectrum as a function of vertical wavenumber determined by the buoyancy force variance flux. In this model, the physically important notion of scale is determined by the turbulent dynamics, it is not given a priori (i.e. the by usual Euclidean distance). The 23/9-D FIF model is the most physically and empirically satisfying, being based on turbulent (spectral) fluxes. The FIF model as originally proposed by Schertzer and Lovejoy is actually a vast family of scaling models broadly compatible with turbulent phenomenology and with the classical turbulent laws of Kolmogorov, Corrsin and Obukov. However, until now it has mostly been developed on the basis of structures localized in space,time. In this paper, we show how to construct extreme FIF models with wave-like structures which are localized in space but unlocalized in space,time, as well as a continuous family of intermediate models which are akin to Lumley,Shur models in which some part of the localized turbulent energy ,leaks' into unlocalized waves. The key point is that the FIF requires two propagators (space,time Green's functions) which can be somewhat different. The first determines the space,time structure of the cascade of fluxes; this must be localized in space,time in order to satisfy the usual turbulence phenomenology. In contrast, the second propagator relates the turbulent fluxes to the observables; although the spatial part of the propagator is localized as before, in space,time it can be unlocalized. (It is still localized in space, now in wave packets.) We display numerical simulations which demonstrate the requisite (anisotropic, multifractal) statistical properties as well as wave-like phenomenologies. In parts II and III we will examine the empirical evidence for the spatial and temporal parts, respectively, of the model using state-of-the-art lidar data of aerosol backscatter ratios (which we use as a surrogate for passive scalar concentration). Copyright © 2008 Royal Meteorological Society [source] The effect of small-scale hills on orographic dragTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 627 2007S. B. Vosper Abstract The purpose of this study is to investigate the extent to which the presence of hills with relatively short horizontal scales can influence the drag, due to mountain waves and flow blocking, exerted on the flow by larger-scale mountains. Numerical simulations of stratified flow over mountains are presented for flow over orography described by the linear superposition of broad mountains, whose length scales are large enough to generate mountain waves, and narrow corrugations, whose wavelengths fall below the minimum horizontal wavelength for stationary gravity waves. Results are presented for both two- and three-dimensional mountain shapes, and for a range of corrugation heights. It is shown that the corrugations can significantly reduce the amplitude of the mountain waves generated by the broader mountain, or they can suppress the unsteadiness of the wake. When these mechanisms make an important contribution to the total drag, this implies a significant drop in the total drag, compared to the sum of the contributions from the two scales of orography. From the point of view of drag parametrization, the extent to which the effect of the small-scale hills can be represented via an effective roughness length is investigated. © Crown Copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd [source] Variability in the summertime coastal marine atmospheric boundary-layer off California, USATHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004Linda Ström Abstract An analysis of boundary-layer structure and surface-layer turbulence from measurements off the California coast is presented from data collected by research aircraft during two field experiments: the Coastal Waves 1996 (CW96) and the Monterey Area Ship Track (MAST) experiments. CW96 covers the near-coast region, in particular in the vicinity of major headlands, whereas MAST extends offshore. Along the US west coast, coastal modification of the along-coast flow occurs on two main horizontal scales. Firstly, a large-scale variability is due to the interplay between the shallow near-coast marine atmospheric boundary-layer (MABL) and the coastal terrain, typically higher than the MABL depth. The MABL depth decreases smoothly towards the coast while the wind speed increases to a coastal jet in response to the sloping MABL inversion. Secondly, the flow is affected by supercritical flow dynamics. As the wind speed increases and the MABL depth decreases towards the coast, the MABL flow becomes supercritical in a shallow-water sense. As supercritical shallow-water flow interacts with major headlands, expansion fans form, affecting both the wind speed and the MABL depth. The combination of CW96 and MAST data reveals significant differences between the flow along the coast and that far offshore. MABL winds are stronger near the coast whereas aloft the winds are weaker than offshore. The near-coast MABL is also better mixed. Turbulence increases towards the coast while the sensible-heat flux decreases and often changes sign, leading to stable stratification near the coast. A length-scale determining the across-coast influence of the expansion fans is defined from simple inviscid and irrotational shallow-water theory. Data from four days of the CW96 experiment show that this simple theory describes the low-level wind speed adequately. Surface-layer turbulence also scales with this simple length-scale, but the results are complicated by upwelling of cold water, giving rise to strong internal boundary-layers. From terms in the turbulent-energy budgets it appears that dissipation of turbulence exceeds local production. Copyright © 2004 Royal Meteorological Society [source] Distribution of benthic communities in the fjord-like Bathurst Channel ecosystem, south-western Tasmania, a globally anomalous estuarine protected areaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2010Neville S. Barrett Abstract 1.Benthic assemblages in the fjord-like Bathurst Channel estuarine system, south-western Tasmania, vary over horizontal scales of 1,5,km and vertical scales of 1,10,m. Multivariate analysis indicated a total of eight major assemblages that characterize different sections and depths of the channel. 2.Because tannins in the low-salinity surface water layer block light, foliose algae reach 5,m depth in the marine western region but do not penetrate below 1,m in the east. By contrast, sessile invertebrates are most abundant below 5,m depth in the west and below 2,m in the east. Deeper assemblages are unlikely to be continuous with assemblages in deeper waters off the Tasmanian coast as they are highly constrained by depth within particular sections of the estuary. 3.While the species composition of the Bathurst Channel biota is most similar to that found elsewhere in Tasmania, the structural character of the biota in terms of major taxonomic groups is more closely allied to that found in fjords of south-western Chile and south-western New Zealand. These three regions all possess wilderness settings, high rainfall that is channelled through estuaries as a low-salinity surface layer, deep-water emergence of fauna, rapid change in biotic communities over short horizontal and vertical distances, and high levels of local endemism. They also include some of the most threatened aquatic ecosystems on earth due to increasing human activity from a near pristine base, and the potentially catastrophic impacts of climate change. Copyright © 2009 John Wiley & Sons, Ltd. 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