Surface heating in relation to air temperature,wind and turbulence in an urban street canyon     

B. Offerle  I. Eliasson  C. S. B. Grimmond  B. Holmer 《Boundary-Layer Meteorology》2007,122(2):273-292

Wind and temperature measurements from within and above a deep urban canyon (height/width = 2.1) were used to examine the thermal structure of air within the canyon, exchange of heat with the overlying atmosphere, and the possible impacts of surface heating on within-canyon air flow. Measurements were made over a range of seasons and primarily analysed for sunny days. This allowed the study of temperature differences between opposing canyon walls and between wall and air of more than 15°C in summer. The wall temperature patterns follow those of incoming solar radiation loading with a secondary daytime effect from the longwave exchange between the walls. In winter, the canyon walls receive little direct solar radiation, and temperature differences are largely due to anthropogenic heating of the building interiors. Cool air from aloft and heated air from canyon walls is shown to circulate within the canyon under cross-canyon flow. Roofs and some portions of walls heat up rapidly on clear days and have a large influence on heat fluxes and the temperature field. The magnitude and direction of the measured turbulent heat flux also depend strongly on the direction of flow relative to surface heating. However, these spatial differences are smoothed by the shear layer at the canyon top. Buoyancy effects from the heated walls were not seen to have as large an impact on the measured flow field as has been shown in numerical experiments. At night canyon walls are shown to be the source of positive sensible heat fluxes. The measurements show that materials and their location, as well as geometry, play a role in regulating the heat exchange between the urban surface and atmosphere.  相似文献   

News and notes: Environmental change and human health in countries of Africa, the Caribbean and the Pacific     

Gordon McGranahan  Simon Lewin  Taryn Fransen  Caroline Hunt  Marianne Kjellén  Jules Pretty  Carolyn Stephens  Ivar Virgin 《Global Change & Human Health》2000,1(1):9-9

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Mid-Holocene hemlock decline and diatom communities in van Nostrand Lake, Ontario, Canada     

Jeannine-Marie St. Jacques  Marianne Douglas  J.H. McAndrews 《Journal of Paleolimnology》2000,23(4):385-397

Terrestrial ecosystem disturbances inferred from the fossil hemlock pollen decline (ca. 4,800 BP) and recovery (ca. 3,800 BP) affected van Nostrand Lake, including the diatom communities. Ecological models suggest the lake responded by eutrophying, reflecting higher nutrient influx resulting from increased erosion. A decline in lake productivity followed as the forest vegetation recovered and erosion slowed. Lastly, as the forest switched from early and middle successional species to mature species, lake productivity increased as erosion increased nutrient inflow, especially phosphorus. However, this eutrophication response was delayed or buffered, perhaps due to wetland development surrounding the lake. The lake never fully returned to its initial, pre-hemlock decline state, but oscillated between more eutrophic and more mesotrophic or oligotrophic stages, possibly reflecting other disturbances in the catchment and climatic change.  相似文献   

A statistical downscaling algorithm for thermal comfort applications     

David Rayner  Fredrik Lindberg  Sofia Thorsson  Björn Holmer 《Theoretical and Applied Climatology》2015,122(3-4):729-742

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A model for inferring dissolved organic carbon (DOC) in lakewater from visible-near-infrared spectroscopy (VNIRS) measures in lake sediment     

Alexandra Rouillard  Peter Rosén  Marianne S. V. Douglas  Reinhard Pienitz  John P. Smol 《Journal of Paleolimnology》2011,46(2):187-202

We developed an inference model to infer dissolved organic carbon (DOC) in lakewater from lake sediments using visible-near-infrared spectroscopy (VNIRS). The inference model used surface sediment samples collected from 160 Arctic Canada lakes, covering broad latitudinal (60–83°N), longitudinal (71–138°W) and environmental gradients, with a DOC range of 0.6–39.6 mg L⁻¹. The model was applied to Holocene lake sediment cores from Sweden and Canada and our inferences are compared to results from previous multiproxy paleolimnological investigations at these two sites. The inferred Swedish and Canadian DOC profiles are compared, respectively, to inferences from a Swedish-based VNIRS-total organic carbon (TOC) model and a Canadian-based diatom-inferred (Di-DOC) model from the same sediment records. The 5-component Partial Least Squares (PLS) model yields a cross-validated (CV) R_CV² R_{CV}^{2}  = 0.61 and a root mean squared error of prediction (RMSEP _CV ) = 4.4 mg L⁻¹ (11% of DOC gradient). The trends inferred for the two lakes were remarkably similar to the VNIRS-TOC and the Di-DOC inferred profiles and consistent with the other paleolimnological proxies, although absolute values differed. Differences in the calibration set gradients and lack of analogous VNIRS signatures in the modern datasets may explain this discrepancy. Our results corroborate previous geographically independent studies on the potential of using VNIRS to reconstruct past trends in lakewater DOC concentrations rapidly.  相似文献   

WINTER LAND BREEZE IN A HIGH LATITUDE COMPLEX COASTAL AREA     

Björn Holmer  Marie Haeger-Eugensson 《自然地理学》2013,34(2):152-172

The winter land breeze (WLB) was studied in an area with complex topography on the Swedish West Coast (58°N). Methods used were mapping directions of smoke plumes, temperature soundings by tethered balloon and helicopter, three years of monitoring temperature and wind at three levels on a suspension bridge and on a mast, and meteorological observations from three stations located at different distances from the coast. To initiate the development of the WLB, the necessary temperature difference between sea and land was 5°C, but the magnitude of the difference appeared to have little influence. The direction of the typical WLB was at an oblique angle to the coast. The WLB started with a sudden wind shift as a result of frictional decoupling from the prevailing synoptic wind caused by increased stability. The flow, with a depth of about 100 m, developed within the nocturnal inversion at the level of the plateau-shaped mountains and overrode the cold air in the valleys and followed the uplifted inversion over the city of Göteborg. The different layers in the inversion were tilted toward the sea with an inclination similar to the slope of the terrain. In a layer above the WLB but also within the inversion, there was an onshore wind that might be the return flow to the WLB. [Key words: winter land breeze (WLB), decoupling, overriding, urban heat island circulation (UHIC), high latitude, Sweden.]  相似文献   

Contrasting the effects of climatic, nutrient, and oxygen dynamics on subfossil chironomid assemblages: a paleolimnological experiment from eutrophic High Arctic ponds     

Emily M. Stewart  Neal Michelutti  Jules M. Blais  Mark L. Mallory  Marianne S. V. Douglas  John P. Smol 《Journal of Paleolimnology》2013,49(2):205-219

Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds.  相似文献   

An isotope study of the sources of nitrate in Malta’s groundwater     

Tim H.E. Heaton  Marianne E. Stuart  Manuel Sapiano  Miriam Micallef Sultana 《Journal of Hydrology》2012

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The thickness and structural characteristics of the crust across Tibetan plateau from active-sources seismic profiles     

Marianne Karplus 《地震学报(英文版)》2009,(1):21-31

The Tibetan plateau as one of the youngest orogen on the Earth was considered as the result of continent-continent collision between the Eurasian and Indian plates.The thickness and structure of the crust beneath Tibetan plateau is essential to understand deformation behavior of the plateau.Active-source seismic profiling is most available geo-physical method for imaging the structure of the continental crust.The results from more than 25 active-sources seismic profiles carried out in the past twenty years ...  相似文献   

Impact of pond aquaculture effluents on seagrass performance in NE Hainan,tropical China     

Lucia S. Herbeck  Miriam Sollich  Daniela Unger  Marianne Holmer  Tim C. Jennerjahn 《Marine pollution bulletin》2014

The impact of pond aquaculture effluents on the distribution and performance of seagrasses was examined in NE Hainan, tropical China. Samples were taken along transects in three back-reef areas with different extent of aquaculture production in their hinterland. High δ¹⁵N in seagrass leaves and epiphytes (6–9‰) similar to values in pond effluents documented aquaculture as dominant nitrogen source in the back-reefs with decreasing impact with distance from shore. Seagrass species abundance, shoot density and biomass were lower and concentrations of nutrients, chlorophyll and suspended matter were higher at nearshore sites with high and moderate pond abundance than at the control site. High epiphyte loads and low δ³⁴S in seagrass leaves suggest temporal shading and sulphide poisoning of the nearshore seagrasses. Observed gradients in environmental parameters and seagrass performance indicate that the distance from the pond outlets and size of the adjacent pond agglomeration are major determinants of seagrass degradation.  相似文献