South Australian rainfall variability and climate extremes   总被引：1，自引：0，他引：1  

Alexander D. Evans  John M. Bennett  Caecilia M. Ewenz 《Climate Dynamics》2009,33(4):477-493

Rainfall extremes over South Australia are connected with broad-scale atmospheric rearrangements associated with strong meridional sea surface temperature (SST) gradients in the eastern Indian Ocean. Thirty-seven years of winter radiosonde data is used to calculate a time series of precipitable water (PW) and convective available potential energy (CAPE) in the atmosphere. Principle component analysis on the parameters of CAPE and PW identify key modes of variability that are spatially and seasonally consistent with tropospheric processes over Australia. The correlation of the leading principle component of winter PW to winter rainfall anomalies reveal the spatial structure of the northwest cloudband and fronts that cross the southern half of the continent during winter. Similarly the second and third principle components, respectively, reveal the structures of the less frequent northern and continental cloudbands with remarkable consistency. 850 hPa-level wind analysis shows that during dry seasons, anomalous offshore flow over the northwest of Australia inhibits advection of moisture into the northwest, while enhanced subsidence from stronger anticyclonic circulation over the southern half of the continent reduces CAPE. This coincides with a southward shift of the subtropical ridge resulting in frontal systems passing well to the south of the continent, thus producing less frequent interaction with moist air advected from the tropics. Wet winters are the reverse, where a weaker meridional pressure gradient to the south of the continent allows rain-bearing fronts to reach lower latitudes. The analysis of SSTs in the Indian Ocean indicate that anomalous warm (cool) waters in the southeast Indian Ocean coincide with a southward (northward) shift in the subtropical ridge during dry (wet) seasons.  相似文献   

Aerodynamic Scaling for Estimating the Mean Height of Dense Canopies   总被引：1，自引：1，他引：0  

Taro Nakai  Akihiro Sumida  Kazuho Matsumoto  Ken’ichi Daikoku  Shin’ichi Iida  Hotaek Park  Mie Miyahara  Yuji Kodama  Alexander V. Kononov  Trofim C. Maximov  Hironori Yabuki  Toshihiko Hara  Takeshi Ohta 《Boundary-Layer Meteorology》2008,128(3):423-443

We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h _a as the most effective means of resolving the representative canopy height for all forests. We determined h _a by simple linear regression between zero-plane displacement d and roughness length z ₀, without the need for stand inventory data. The applicability of h _a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h _a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z ₀ was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h _a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h _a was also verified using data from several previous studies.  相似文献   

Opportunities provided by geographic information systems and volunteered geographic information for a timely emergency response during flood events in Cologne,Germany     

Tzavella  Katerina  Fekete  Alexander  Fiedrich  Frank 《Natural Hazards》2017,91(1):29-57

The occurrence of disasters such as extreme flooding in urban environments has severe consequences, not only on the human population but also on critical infrastructures such as the road networks, which are of vital importance for everyday living and particularly for emergency response. In this article, our main goal is to present-conceptually and in praxis-a model that could be used from the emergency responders for timely and efficient emergency management and response in an urban complex environment. For the city of Cologne in Germany, we aim to indicate possible ways to decrease the emergency response time during an extreme flood scenario through the development of an accessibility indicator, which consists of different components. Therefore, we will investigate the opportunities that occur, in a flood risk scenario, from the use of geographic information in different forms such as Volunteered Geographic Information (VGI) and open-source data in an ArcGIS environment, to increase urban resilience through the decreasing emergency response time. We will focus on network analysis for the fire brigades (first acting emergency responders) during a flood scenario to calculate their emergency response ranges and emergency response routes through flooded road networks, for the assistance of the possibly affected hospitals, refugee homes and fire brigades, which can be flooded. At the end of the paper, we suggest that the vulnerable community of the refugees could be taken into consideration as a new source of VGI, as an additional component that would lead to the decrease in the emergency response time. The geo-located information that could be provided by the refugee community can be very useful in emergency situations, such as those examined in this article where timely information can be forwarded to the proper authorities for a more focused and timely emergency response, increasing the resilience of the urban population and their community.

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Englacial and subglacial water flow at Skálafellsjökull,Iceland derived from ground penetrating radar,in situ Glacsweb probe and borehole water level measurements          下载免费PDF全文

Jane K. Hart  Kathryn C. Rose  Alexander Clayton  Kirk Martinez 《地球表面变化过程与地形》2015,40(15):2071-2083

We reconstruct englacial and subglacial drainage at Skálafellsjökull, Iceland, using ground penetrating radar (GPR) common offset surveys, borehole studies and Glacsweb probe data. We find that englacial water is not stored within the glacier (water content ~0–0.3%). Instead, the glacier is mostly impermeable and meltwater is able to pass quickly through the main body of the glacier via crevasses and moulins. Once at the glacier bed, water is stored within a thin (1 m) layer of debris‐rich basal ice (2% water content) and the till. The hydraulic potential mapped across the survey area indicates that when water pressures are high (most of the year), water flows parallel to the margin, and emerges 3 km down glacier at an outlet tongue. GPR data indicates that these flow pathways may have formed a series of braided channels. We show that this glacier has a very low water‐storage capacity, but an efficient englacial drainage network for transferring water to the glacier bed and, therefore, it has the potential to respond rapidly to changes in melt‐water inputs. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Sexual reproduction of Hippospongia communis (Lamarck, 1814) (Dictyoceratida,Demospongiae): comparison of two populations living under contrasting environmental conditions     

Souad Zarrouk  Alexander V. Ereskovsky  Karim Ben Mustapha  Amor El Abed  Thierry Pérez 《Marine Ecology》2013,34(4):432-442

The study of the reproductive processes of benthic invertebrates is essential to the understanding of their population dynamics and is also important in formulating conservation plans, especially for exploited species. The sexual reproduction of Hippospongia communis, the ‘honeycomb’ bath sponge, was studied at two locations in the Mediterranean Sea: the Kerkennah Islands (Tunisia, South Mediterranean), where the mean annual seawater temperature is 19 °C, and Marseille (France, Northwestern Mediterranean Sea), where the mean annual water temperature is 16 °C. The aim of this comparative study was to determine whether different environmental conditions could affect reproduction patterns. At both locations, H. communis was found to contain sexual reproductive elements year‐round. Oogenesis and embryogenesis occurred throughout the year, whereas spermatogenesis occurred during shorter periods between October and November, in both populations. While gametogenesis seemed to be synchronized, indicating that fertilization could occur at the same time at both locations, spawning was observed in late summer in Marseille, whereas it started in late spring for the Kerkennah population. Larval development of H. communis seems to take longer for sponges living at cooler locations such as Marseille. Reproductive effort calculated for both sexes showed significantly higher values for specimens from Kerkennah Islands. By comparing sexual reproductive patterns of populations living in two contrasted environments, we suggest that a change of thermal regime can affect H. communis phenology.  相似文献   

A multi-data set comparison of the vertical structure of temperature variability and change over the Arctic during the past 100?years     

Stefan Br?nnimann  Andrea N. Grant  Gilbert P. Compo  Tracy Ewen  Thomas Griesser  Andreas M. Fischer  Martin Schraner  Alexander Stickler 《Climate Dynamics》2012,39(7-8):1577-1598

We compare the daily, interannual, and decadal variability and trends in the thermal structure of the Arctic troposphere using eight observation-based, vertically resolved data sets, four of which have data prior to 1948. Comparisons on the daily scale between historical reanalysis data and historical upper-air observations were performed for Svalbard for the cold winters 1911/1912 and 1988/1989, the warm winters 1944/1945 and 2005/2006, and the International Geophysical Year 1957/1958. Excellent agreement is found at mid-tropospheric levels. Near the ground and at the tropopause level, however, systematic differences are identified. On the interannual time scale, the correlations between all data sets are high, but there are systematic biases in terms of absolute values as well as discrepancies in the magnitude of the variability. The causes of these differences are discussed. While none of the data sets individually may be suitable for trend analysis, consistent features can be identified from analyzing all data sets together. To illustrate this, we examine trends and 20-year averages for those regions and seasons that exhibit large sea-ice changes and have enough data for comparison. In the summertime Pacific Arctic and the autumn eastern Canadian Arctic, the lower tropospheric temperature anomalies for the recent two decades are higher than in any previous 20-year period. In contrast, mid-tropospheric temperatures of the European Arctic in the wintertime of the 1920s and 1930s may have reached values as high as those of the late 20th and early 21st centuries.  相似文献   

Extraordinary C enrichment of diether lipids at the Lost City Hydrothermal Field indicates a carbon-limited ecosystem     

Alexander S. Bradley  John M. Hayes 《Geochimica et cosmochimica acta》2009,73(1):102-2869

Active and inactive carbonate chimneys from the Lost City Hydrothermal Field contain up to 0.6% organic carbon with diverse lipid assemblages. The δ¹³C values of total organic carbon range from −21.5‰ vs. VPDB at an extinct carbonate chimney to −2.8‰ at a 70 °C, actively venting carbonate chimney. Samples collected at locations with total organic carbon with δ¹³C > −15‰ also contained high abundances of isoprenoidal and nonisoprenoidal diether lipids. Samples with TOC more depleted in ¹³C lacked or contained lower amounts of these diethers.Isoprenoidal diethers, including sn-2 hydroxyarchaeol, sn-3 hydroxyarchaeol, and putative dihydroxyarchaeol, are likely to derive from methanogenic archaea. These compounds have δ¹³C values ranging from −2.9 to +6.7‰ vs. VPDB. Nonisoprenoidal diethers and monoethers are presumably derived from bacteria, and have structures similar to those produced by sulfate-reducing bacteria in culture and at cold seeps. In samples that also contained abundant hydroxyarchaeols, these diethers have δ¹³C values between −11.8 and +3.6‰. In samples without abundant hydroxyarchaeols, the nonisoprenoidal diethers were typically more depleted in ¹³C, with δ¹³C as low as −28.7‰ in chimneys and −45‰ in fissures.The diethers at Lost City are probably derived from hydrogen-consuming methanogens and bacteria. High hydrogen concentrations favor methanogenesis over methanotrophy and allow the concurrent growth of methanogens and sulfate-reducing bacteria. The unusual enrichment of ¹³C in lipids can be attributed to nearly complete consumption of bioavailable carbon in vent fluids. Under carbon-limited conditions, the isotope effects that usually lead to ¹³C-depletion in organic material cannot be expressed. Consequently, metabolic products such as lipids and methane have δ¹³C values typical of abiotic carbon.  相似文献   

Highly siderophile element evidence for early solar system processes in components from ordinary chondrites   总被引：1，自引：0，他引：1  

M.F. Horan  C.M.O’D. Alexander 《Geochimica et cosmochimica acta》2009,73(22):6984-4036

Separated magnetic and nonmagnetic components from the ordinary chondrites Dhajala (H3.8) and Ochansk (H4) were analyzed for their Re-Os isotopic compositions, as well as for the abundances of the highly siderophile elements (HSE) Re, Os, Ir, Ru, Pt and Pd. The Re-Os isotopic systematics of these components are used to constrain the timing of HSE fractionations, and assess the level of open-system behavior of these elements in each of the different components. The high precision, isotope dilution mass spectrometric analyses of the HSE are used to constrain the origins of, and possible relations between some of the diverse components present in these chondrites. The relative and absolute abundances of the HSE differ considerably among the components. Metal fractions have Re/Os that are factors of ∼2 (Dhajala) to ∼3 (Ochansk) higher than those of their nonmagnetic fractions. The isotopic data for both meteorites are consistent with the largest Re-Os fractionations occurring between metal and nonmagnetic components early in solar system history, although minor to moderate late stage, open-system behavior, and limited variations in Re/Os preclude a precise determination of the age for that fractionation. Open-system behavior is generally absent to minor in the metal fractions, and highly variable in nonmagnetic fractions. Re/Os ratios of nonmagnetic fractions deviate as much as 40% from a primordial isochron. Although some deviations are large for isochron applications, nearly all are negligible with respect to consideration of fractionation processes controlling the HSE.Metal from both meteorites contains about 90% of the total budget of HSE. Metal in Ochansk has ∼2 to 10 times the abundances of the bulk meteorite, while metal from the matrix of Dhajala has ∼2 to 4 times the abundances of the bulk. Fine metal in both meteorites has higher abundances than coarse metal, as has been previously observed. Nonmagnetic components, consisting of chondrules and matrix from which metal was removed in the laboratory, have highly fractionated HSE, characterized by much lower Re/Os than the bulk meteorites, as well as large relative depletions in Pd. The abundances of Re, Os, Ir, Ru and Pt in the nonmagnetic fractions are 14-120 ng/g, much higher than would be expected if they had equilibrated with the metal phases present (150-16,000 ng/g). Collectively, the data are consistent with the HSE budget in ordinary chondrites being dominated by two HSE-bearing carrier phases with distinct compositions. These phases formed separately, and never subsequently equilibrated. Metal components incorporated a HSE carrier that formed at high through moderate temperatures and relatively high pressures, such that the relatively volatile Pd behaved coherently with the more refractory HSE. Nonmagnetic fractions from both chondrules and matrix have HSE compositions that likely require at least two processes that fractionated the HSE. Depletions in Pd are consistent with the presence of HSE carriers that formed as either highly refractory condensates, or residues of high degrees of metal melting. Depletions in Re may implicate a period of relatively high f_O2 during which a volatile form of Re was separated from the other HSE.  相似文献   

Geology and geochemistry of the Mammoth breccia pipe,Copper Creek mining district,southeastern Arizona: evidence for a magmatic–hydrothermal origin     

Eric D. Anderson  William W. AtkinsonJr.  Timothy Marsh  Alexander Iriondo 《Mineralium Deposita》2009,44(2):151-170

The Copper Creek mining district, southeastern Arizona, contains more than 500 mineralized breccia pipes, buried porphyry-style, copper-bearing stockworks, and distal lead–silver veins. The breccia pipes are hosted by the Copper Creek Granodiorite and the Glory Hole volcanic rocks. The unexposed Mammoth breccia pipe, solely recognized by drilling, has a vertical extent of 800 m and a maximum width of 180 m. The pipe consists of angular clasts of granodiorite cemented by quartz, chalcopyrite, bornite, anhydrite, and calcite. Biotite ⁴⁰Ar/³⁹Ar dates suggest a minimum age of 61.5 ± 0.7 Ma for the host Copper Creek Granodiorite and ⁴⁰Ar/³⁹Ar dates on hydrothermal sericite indicate an age of 61.0 ± 0.5 Ma for copper mineralization. Fluid inclusion studies suggest that a supercritical fluid with a salinity of approximately 10 wt.% NaCl equiv. condensed to a dilute aqueous vapor (1–2.8 wt.% NaCl equiv.) and a hypersaline brine (33.4–35.1 wt.% NaCl equiv.). Minimum trapping temperatures are 375°C and trapping depths are estimated at 2 km. Sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization of 469 ± 25°C. Calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from 10.2‰ to 13.4‰ and −60‰ to −39‰, respectively, suggesting that the mineralizing fluid was dominantly magmatic. Evidence from the stable isotope and fluid inclusion analyses suggests that the fluids responsible for Cu mineralization within the Mammoth breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe.  相似文献   

Structural diversity of diether lipids in carbonate chimneys at the Lost City Hydrothermal Field     

Alexander S. Bradley  Helen Fredricks  Kai-Uwe Hinrichs  Roger E. Summons 《Organic Geochemistry》2009,40(12):1169-1178

The Lost City Hydrothermal Field hosts a distinctive microbial ecosystem that is supported by the products of serpentinization reactions. The calcium carbonate chimneys here contain abundant isoprenoidal and non-isoprenoidal ether lipids, the structural diversity of which is similar to that found in carbonate crusts at cold seeps where anaerobic oxidation of methane (AOM) is the dominant biogeochemical process. The microbial community at Lost City includes abundant archaea, which largely belong to a single phylotype within the methanogenic Methanosarcinales. Isoprenoidal diethers derived from these archaea have polar head groups comprising phosphatidylglycerol or monoglycosyl moieties, although many isoprenoidal diethers detected in these carbonates lack head groups.The non-isoprenoidal diether lipids at Lost City are largely glycolipids. Glycosydic non-isoprenoidal diethers have not previously been reported from any environments or bacterial isolates. Glycolipids are common in archaea where they contain isoprenoidal hydrocarbon cores ether linked to glycerol. Glycolipids also occur in some bacteria and in these non-isoprenoidal fatty acid chains are ester linked to glycerol. However, the glycosylated non-isoprenoidal diether lipids at Lost City contain a previously undetected combination of archaeal and bacterial traits that might be an adaptive response to the vent environment. We hypothesize that utilization of glycosyl head groups instead of phosphatidyl head groups is a strategy for conservation of phosphate by organisms growing in fluids low in this essential nutrient.  相似文献