A Lagrangian particle dispersion model (LPDM) driven by velocity fields from large-eddy simulations (LESs) is used to determine the mean and variability of plume dispersion in a highly convective planetary boundary layer (PBL). The total velocity of a “particle” is divided into resolved and unresolved or random (subfilter scale, SFS) velocities with the resolved component obtained from the LES and the SFS velocity from a Lagrangian stochastic model. This LPDM-LES model is used to obtain an ensemble of dispersion realizations for calculating the mean, root-mean-square (r.m.s.) deviation, and fluctuating fields of dispersion quantities. An ensemble of 30 realizations is generated for each of three source heights: surface, near-surface, and elevated. We compare the LPDM calculations with convection tank experiments and field observations to assess the realism of the results. The overall conclusion is that the LPDM-LES model produces a realistic range of dispersion realizations and statistical variability (i.e., r.m.s. deviations) that match observations in this highly convective PBL, while also matching the ensemble-mean properties. This is true for the plume height or trajectory, vertical dispersion, and the surface values of the crosswind-integrated concentration (CWIC), and their dependence on downstream distance. One exception is the crosswind dispersion for an elevated source, which is underestimated by the model. Other analyses that highlight important LPDM results include: (1) the plume meander and CWIC fluctuation intensity at the surface, (2) the applicability of a similarity theory for plume height from a surface source to only the very strong updraft plumes—not the mean height, and (3) the appropriate variation with distance of the mean surface CWIC and the lower bound of the CWIC realizations for a surface source. 相似文献
A system-theoretic approach is proposed to investigate the feasibility of reconstructing a sound velocity profile (SVP) from acoustical hydrophone measurements. A state-space representation of the normal-mode propagation model is used. It is shown that this representation can be utilized to investigate the so-called observability of the SVP from noisy measurement data. A model-based processor is developed to extract the required information, and it is shown that even in cases where limited SVP information is available, the SVP can be estimated using this approach. Based on this framework, investigations are made of model-based solutions to the sound velocity profile and related parameter estimation problems. In particular, a processor is designed that allows in situ recursive estimation of the sound velocity profile from simulated data 相似文献
Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002. 相似文献
AN AUSTRALIAN DICTIONARY OF ENVIRONMENT AND PLANNING by A. Gilpin. 16 × 24 cm, xvi and 271 pages. Oxford University Press: Melbourne 1990 (ISBN 0 19 554806 X) $A60.00 (hard).
CONTINENT IN CRISIS: A Natural History of Australia by D. Smith, 13 × 20 cm, xii and 201 pages. Penguin: Melbourne 1990 (ISBN 0 14 011169 7) $A14.99 (soft).
THE END OF NATURE by B. McKibben. 14 × 22 cm, xi and 212 pages. Viking: London 1990 (ISBN 0 670 82877 7) $A29.99 (hard); distributed by Penguin Books.
THE FATE OF THE FOREST: Developers, Destroyers and Defenders of the Amazon by S. Hecht and A. Cockburn. 13 × 20 cm, xiii and 349 pages. Penguin: London (ISBN 0 14 013382 8) $A16.99 (soft).
ENVIRONMENT, AID AND REGIONALISM IN THE SOUTH PACIFIC (Pacific Research Monograph No. 22) by J. Carew‐Reid. 17 × 25 cm, xii and 185 pages. National Centre for Development Studies, Australian National University: Canberra 1989 (ISBN 0 7315 0673 1) $A25.00 (soft).
NEW SEEDS AND POOR PEOPLE by M. Lipton with R. Longhurst. 14 × 21 cm, xiv and 473 pages, Unwin Hyman: London 1989 (ISBN 0 04 45326 4) $A39.95 (soft).
CLIMATE CHANGE AND WORLD AGRICULTURE by M. Parry. 15 × 23 cm, xv and 157 pages. Earthscan: London 1990 (ISBN 1 85383 065 8) £9.95 (soft).
INTRODUCTION TO WORLD VEGETATION (Second Edition) by A. S. Collinson. 14 × 21 cm, x and 325 pages. Unwin Hyman: London 1988 (ISBN 0 04 581 030 3) $A95.00 (hard); (ISBN 0 04 581 031 1) $A39.95 (soft).
OCEANS OF LIFE OFF SOUTHERN AFRICA edited by A. I. L. Payne and R. J. M. Crawford. 22 × 29 cm, xii and 380 pages. Vlaeberg: Cape Town 1989 (ISBN 0 947461 01 9) $US30.00 plus $US5.00 postage (hard).
KARST GEOMORPHOLOGY AND HYDROLOGY by D. Ford and P. Williams. 15 × 23 cm, xv and 601 pages. Unwin Hyman: London 1989 (ISBN 0 04 551106 3) $A79.95 (soft).
ENVISIONING INFORMATION by E. R. TUFTE. 22 × 78 cm, 126 pages. Graphics Press: Cheshire, CT 1990 $US48.00 (hard). Available from Graphics Press, Box 430, Cheshire, Connecticut, 06410, USA.
A GUIDE TO REMOTE SENSING: Interpreting Images of the Earth by S. A. Drury. 22 × 27 cm, viii and 199 pages. Oxford University Press: Oxford 1991 (ISBN 0 19 854495 2) $A44.95 (soft).
THE CAINOZOIC IN AUSTRALIA: A Re‐appraisal of the Evidence (Special Publication No. 18) edited by M. A. J. William, P. De Deckker and A. P. Kershaw. 17 × 25 cm, x and 346 pages. Geological Society of Australia Inc: Sydney 1991 (ISBN 0 909869 76 6) $A60.00 (non‐members), $A40.00 (members) (soft).
MONSOONAL AUSTRALIA: Landscape, Ecology and Man in the Northern Lowlands edited by C. D. Haynes, M. G. Ridpath and M. A. J. Williams. 20 × 29 cm, xii and 231 pages. Balkema: Rotterdam 1991 (ISBN 90 6191 638 0) $A85.25 (hard).
SOILS: THEIR PROPERTIES AND MANAGEMENT: A Soil Conservation Handbook for New South Wales edited by P. E. V. Charman and B. W. Murphy. 21 × 27 cm, xix and 363 pages. Sydney University Press: Sydney 1991 (ISBN 0 424 00183 7) $A39.95 (soft).
VEGETATION (Atlas of Australian Resources, Third Series, Volume 6) by Australian Surveying and Land Information Group. 30 × 43 cm, 64 pages. Australian Surveying and Land Information Group: Canberra 1990 (ISBN 0 642 14993 3) $A39.95 (soft).
THE ATLAS OF NEPAL IN THE MODERN WORLD by M. Sill and J. Kirkby. 27 × 22 cm, 160 pages. Earthscan: London 1991 (ISBN 1 85383 032 1) £37.50 (hard).
DEVELOPMENT IN PRACTICE: Paved With Good Intentions by D. Porter, B. Allen and G. Thompson. 15 × 23 cm. Routledge: London 1990 (ISBN 0 415 16626 3) $A27.95 (soft); distributed by The Law Book Co.
CHINA'S SPATIAL ECONOMY: Recent Developments and Reforms edited by G. J. R. Linge and D. K. Forbes. 15 × 22 cm, xiii and 225 pages. Oxford University Press: Hong Kong 1991 (ISBN 0 19 585296 6) $A29.95 (hard). 相似文献
During the 2005 Layered Organization in the Coastal Ocean (LOCO) field program in Monterey Bay, California, we integrated intensive water column surveys by an autonomous underwater vehicle (AUV) with satellite and mooring data to examine the spatiotemporal scales and processes of phytoplankton thin-layer development. Surveying inner to outer shelf waters repeatedly between August 18 and September 6, the AUV acquired 6841 profiles. By the criteria: [(1) thickness ≤3 m at the full-width half-maximum, (2) peak chlorophyll at least twice the local background concentrations, and (3) a corresponding peak in optical backscattering], thin layers were detected in 3978 (58%) of the profiles. Average layer thickness was 1.4 m, and average intensity was 13.5 μg l?1 above (3.2x) background. Thin layers were observed at depths between 2.6 and 17.6 m, and their depths showed diurnal vertical migration of the layer phytoplankton populations. Horizontal scales of thin-layer patches ranged from <100 m to>10,000 m. A thin-layer index (TLI), computed from layer frequency, intensity and thinness, was highest in mid-shelf waters, coincident with a frontal zone between bay waters and an intrusion of low-salinity offshore waters. Satellite observations showed locally enhanced chlorophyll concentrations along the front, and in situ observations indicated that phytoplankton may have been affected by locally enhanced nutrient supply in the front and concentration of motile populations in a convergence zone. Minimum TLI was furthest offshore, in the area most affected by the intrusion of offshore, low-chlorophyll waters. Average thin-layer intensity doubled during August 25–29, in parallel with warming at the surface and cooling within and below the thermocline. During this apparent bloom of thin-layer populations, density oscillations in the diurnal frequency band increased by an order of magnitude at the shelfbreak and in near-bottom waters of the inner shelf, indicating the role of internal tidal pumping from Monterey Canyon onto the shelf. This nutrient transport process was mapped by the AUV. Peak TLI was observed on August 29 during a nighttime survey, when phytoplankton were concentrated in the nutricline. Empirical orthogonal function decomposition of the thin-layer particle size distribution data from this survey showed that throughout the inner to outer shelf survey domain, the layers were dominated by phytoplankton having a cross-section of ～50 μm. This is consistent with the size of abundant Akashiwo sanguinea cells observed microscopically in water samples. During a subsequent and stronger intrusion of low-salinity offshore waters, spatially-averaged vertical density stratification decreased by > 50%, and phytoplankton thin layers disappeared almost completely from the AUV survey domain. 相似文献
During the summers of 2005 and 2006, experiments designed to understand the properties of densely concentrated, thin layers of plankton and the processes governing their dynamics were conducted in Monterey Bay, California, USA. Our goal was to elucidate the role that species-specific properties of phytoplankton play in thin layer dynamics. Using adaptive sampling, we collected water samples from inside and outside bio-optical features of the water column. Characterization of the phytoplankton was compiled from live and preserved samples, and analyzed within a framework of physical, optical, chemical and acoustical data. In both years, Monterey Bay was home to an extraordinarily diverse assemblage of phytoplankton and other protists. Bioluminescent dinoflagellates, and Harmful Algal Bloom (HAB) taxa were common. In 2005, community assemblages were widespread, thus advection of water through the experimental mooring array did not result in floristic changes. In 2006 phytoplankton were very patchy in horizontal distribution, and advection of water through the array was at times accompanied by dramatic shifts in community composition. Individual taxa often exhibited disparate patterns of vertical distribution, with some found throughout the water column, whereas others were restricted to narrow depth intervals. Thin layers were observed in both years. In 2005, the dinoflagellate Akashiwo sanguinea formed intense thin layers near the pycnocline at night, and migrated to near surface waters at dawn. In 2006, layer composition was more complex, and related to the water mass present at the time of sampling. Optically detected thin layers of phytoplankton can be studied from the perspective of the impact their high biomass has on both ecological processes, and ocean optics. But thin layers can also be studied from the species-specific perspective of each organism, its role within the thin layer habitat, and the impact that life within a thin layer has on its life history and ecology. Several low-abundance taxa appeared to be restricted to narrow depth intervals in the water column, and constitute species-specific thin layers with the potential to have a large ecological impact even if their biomass is too low to dominate an optically defined thin layer. Concentration into thin layers may also facilitate obligatory relationships between taxa, such as the hypothesized interrelationships between cryptomonads, Myrionecta rubra, and Dinophysis spp., all of which were observed in this system. Complexity of vertical structure in Monterey Bay rivals that already demonstrated in topographically constrained, stratified systems, and presents challenges to our theoretical framework of phytoplankton ecology. 相似文献
Thin phytoplankton layers are common features in the coastal environment; however sampling these fine-scale optical features across broad horizontal scales remains a challenge. To investigate the horizontal spatial structure of thin phytoplankton layers, we performed an overnight survey in northern Monterey Bay, CA, USA using a SeaSciences Acrobat towed-vehicle. Physical and optical measurements were collected between the surface and near-bottom-depths along four parallel, across-shore transects. Three coherent chlorophyll features were observed: (1) a broad, sub-surface patch at the offshore end, (2) a near-surface patch at the nearshore end, and (3) a deep patch located between the nearshore and offshore patches. The offshore and nearshore patch were separated by a change in seafloor slope and a region of compressed, shoaling isopycnals. Both the offshore and nearshore features were located at the pycnocline, had similar optical properties, and were co-located with a low-salinity intrusion. The deep chlorophyll patch had associated physical and optical properties that were distinct from the patches at the pycnocline. The results from this study further underscore the heterogeneous horizontal spatial structure of thin layers and also add to the growing evidence suggesting that low-salinity intrusions may be strongly linked to the formation of thin phytoplankton layers over the northern shelf of Monterey Bay. 相似文献
