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71.
72.
Ferdinando De Tomasi M. Marcello Miglietta M. Rita Perrone 《Boundary-Layer Meteorology》2011,139(3):521-541
A lidar system is used to determine the diurnal evolution of the planetary boundary layer (PBL) height on a summer day characterized
by anticyclonic conditions. The site is located some 15 km distant from the sea, on a peninsula in south-east Italy. Contrary
to expectations, the PBL height, after an initial growth consequent to sunrise, ceases to increase about 2 h before noon and
then decreases and stabilizes in the afternoon. An interpretation of such anomalous behaviour is provided in terms of trajectories
of air parcels towards the lidar site, which are influenced by the sea breeze, leading to a transition from a continental
boundary layer to a coastal internal boundary layer. The results are analyzed using mesoscale numerical model simulations
and a simple model that allows for a more direct interpretation of experimental results. 相似文献
73.
Rawad Massoud Alan.L Shihadeh Mohamed Roumié Myriam Youness Jocelyne Gerard Nada Saliba Rita Zaarour Maher Abboud Wehbeh Farah Najat Aoun Saliba 《Atmospheric Research》2011,101(4):893-901
The results of the first large scale chemical characterization of PM10 and PM2.5 at three different sites in the urban city of Beirut, Lebanon, are presented. Between May 2009 and April 2010 a total of 304 PM10 and PM2.5 samples were collected by sampling every sixth day at three different sites in Beirut. Observed mass concentrations varied between 19.7 and 521.2 μg m? 3 for PM10 and between 8.4 and 72.2 μg m? 3 for PM2.5, respectively. Inorganic concentrations accounted for 29.7–35.6 μg m? 3 and 46.0–53.5 μg m? 3 of the total mass of PM10 and PM2.5, respectively. Intra-city temporal and spatial variations were assessed based on the study of three factors: correlation coefficients (R) for PM and chemical components, coefficient of divergence (CODs), and source apportionment using positive matrix factorization (PMF). Based on R and COD of PM concentrations, the three sites appear homogeneous. However, when individual elements were compared, heterogeneity among sites was found. This latter was attributed to the variability in the percent contribution of biogenic and local anthropogenic source factors such as traffic related sources and dust resuspension. Other factors included the proximity to the Mediterranean sea, the population density and the topographical structure of the city. Hence, despite its small size (20.8 km2), one PM monitoring site does not reflect an accurate PM level in Beirut. 相似文献
74.
Ammonium,nitrate and phytoplankton interactions in a freshwater tidal estuarine zone: potential effects of cultural eutrophication 总被引:2,自引:0,他引:2
Rita B. Domingues Ana B. Barbosa Ulrich Sommer Helena M. Galvão 《Aquatic Sciences - Research Across Boundaries》2011,73(3):331-343
Nitrate and ammonium are the most important nitrogen sources for phytoplankton growth. Differential utilization of inorganic
nitrogenous compounds by phytoplankton has been observed and may have significant impacts on primary productivity at local
scales. We used enrichment experiments with natural phytoplankton populations from the freshwater tidal zone of the Guadiana
estuary, a coastal ecosystem increasingly subjected to anthropogenic influences, to study the effects of nitrate and ammonium
on N-consumption and phytoplankton growth. In addition, we used combined additions of nitrate and ammonium to understand the
inhibitory effect of ammonium over nitrate uptake. Ammonium concentrations in the freshwater tidal reaches of the Guadiana
estuary throughout the sampling period were too low to exert an inhibitory effect on nitrate uptake or a toxic effect on phytoplankton
growth. Nitrate was clearly the main nitrogen source for phytoplankton at the study site. Overall, nitrate seemed to become
limiting at concentrations lower than 20 μM and N-limitation was particularly significant during summer. A trend of decreasing
nitrate uptake with increasing ammonium concentrations and uptake suggested an overall preference for ammonium. However, preference
for ammonium was group-specific, and it was observed mainly in green algae and cyanobacteria. In fact, cyanobacteria relied
only on ammonium as their N-source. On the contrary, diatoms preferred nitrate, and did not respond to ammonium additions.
The increasing eutrophication in the Guadiana estuary and particularly increased inputs of nitrogen as ammonium due to urban
waste effluents may result in a shift in phytoplankton community composition, towards a dominance of cyanobacteria and green
algae. 相似文献
75.
França S Vasconcelos RP Tanner S Máguas C Costa MJ Cabral HN 《Marine environmental research》2011,72(4):204-215
Stable carbon and nitrogen isotopes (δ13C, δ1?N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs. 相似文献
76.
77.
78.
ISO-SWS spectra of two Mira variables (R Cas and T Dra), taken at two different pulsational phases, are presented. We describe
the reduction of the data and the encountered problems. The dust features observed by ISO at different phases and with the
Low Resolution Spectrometer of IRAS are compared. We briefly discuss the results in terms of current models for the circumstellar
dust shells of AGB variables.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
79.
Josef Hron Walter Nowotny Rita Gautschy-Loidl Susanne Höfner 《Astrophysics and Space Science》2003,286(1-2):213-218
We present synthetic radii and visibilities in the IR, based on hydrostatic and dynamic model atmospheres of carbon stars.
The differences between these two sets of input models and to uniform disc models are discussed and compared to the expected
capabilities of the VLTI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.