Water regime in soils and plants along an aridity gradient in central Baja California, Mexico     

Ernesto Franco-Vizcaíno 《Journal of Arid Environments》1994,27(4)

The Central Desert of Baja California has pronounced climatic gradients. Water storage in the upper metre of soil and leaf water potentials in Larrea tridentata, Simmondsia chinensis and Fouquieria columnaris were monitored during 28 months at six sites. Estimated annual evapotranspiration was 75-150 mm in sandy loams, and 45-60 mm in sandy soils. Cumulative recharge accounted for 80% of precipitation in loams, but only 50% in sands. During the study period, increased aridity was expressed as longer periods of drought, but there was no less recharge. Weak to moderate relationships were found between soil water content and predawn leaf water potential.  相似文献   

The gas-phase reaction of ClONO2 with hydrogen chloride     

Roger Atkinson  Sara M. Aschmann  Ernesto C. Tuazon  Mark A. Goodman  Arthur M. Winer 《Journal of Atmospheric Chemistry》1987,5(1):83-90

The gas-phase reaction of ClONO₂ with HCl was investigated using two large-volume environmental chambers with analysis by in situ long pathlength Fourier transform infrared absorption spectroscopy. In these chambers the reaction was observed to proceed, at least in part, by heterogenous routes, and an upper limit to the rate constant for the homogeneous gas-phase reaction of geneous routes, and an upper limit to the rate constant for the homogeneous gas-phase reaction of $$k\left( {{\text{ClONO}}_{\text{2}} + {\text{HCl}}} \right) < 1.5 \times 10^{ - 19} {\text{ cm}}^{\text{3}} {\text{ molecule}}^{{\text{ - 1}}} {\text{ s}}^{{\text{ - 1}}}$$ Was derived at 298±2K. Assuming that this room-temperature upper limit to the rate constant is applicable to stratospheric temperatures, this homogeneous gas-phase reaction can be estimated to be of negligible importance as a ClONO₂ loss process in the stratosphere.  相似文献   

Atmospheric electricity at Brébeuf college geophysical observatory in Montréal,Canada     

Ernesto E. Gherzi 《Pure and Applied Geophysics》1967,67(1):239-265

Summary The author gives the results obtained by means of nine years (1957–1965 inclusive) of recordings of the potential gradient and two years (1964–1965 inclusive) of the current density. Some general aspects of these registrations are discussed.  相似文献   

Cosmo-SkyMed X-band SAR data for classification of ice-free areas and glacier facies on Potter Peninsula,King George Island Antarctica     

André Medeiros de Andrade  Jorge Arigony-Neto  Ulisses Franz Bremer  Roberto Ferreira Machado Michel  Alice César Fassoni-Andrade  Carlos Ernesto Goncalves Reynaud Schaefer 《国际地球制图》2016,31(7):803-812

The climate change phenomena have been influencing terrestrial and glacial ecosystems around the planet. Maritime Antarctica is especially sensitive to these climate variations and over the last 50 years increasing global air temperatures have caused extensive glacial retreat. The objective of this study is to evaluate the potential use of the SAR technology in monitoring the surface dynamics of the Potter Peninsula, King George Island, maritime Antarctica. An image generated by the SAR satellite COSMO-SkyMed, obtained on 2 February 2011, was used to extract the backscattering values of targets on the surface for further processing and classification, using a supervised statistic classifier of maximum likelihood for the determination of the surface classes. The average backscattering of water bodies presented high similarity, which made its separation unattainable. On the other hand, the surface classes’ bare ice and wet snow over the glacier presented distinct average backscattering values, which allowed an efficient and precise classification using only this parameter. The classification process showed satisfactory results for periglacial environments, presenting high fidelity to the field data.  相似文献   

Quantifying the reefscape transformation of a coastal Caribbean coral reef during a phase shift and the associated coastal landscape change          下载免费PDF全文

Abigail Martínez‐ Rendis  Gilberto Acosta González  José Luis Hernández‐Stefanoni  Jesús Ernesto Arias González 《Marine Ecology》2016,37(3):697-710

Caribbean coral reefs are under strong natural and human pressures and many have undergone phase shifts as a result of local and global change. However few studies have quantified the extent of these phase shifts and the potential impacts that they have on coral reef communities. A temporal comparative analysis of several coral reefscape and landscape metrics was conducted for data from Mahahual, Quintana Roo, Mexico, between the years 2000 and 2006, when a phase shift occurred. Landscape metrics were calculated from coral reef and coastal cover maps obtained by multispectral satellite image classification using IKONOS satellite imagery. These metrics showed that the coastal landscape and reefscape of Mahahual lost 85 ha of vegetation cover and 43 ha of coral cover over 6 years, respectively. Coastal landscape transformation was induced by the construction of a cruise ship pier and multiple associated tourist developments along the coast, such as hotels and restaurants, meanwhile alteration of the reefscape may be associated with potential stressors such as coastal development, bleaching events and hurricanes.  相似文献   

A Pulsed Laser Photolysis-Resonance Fluorescence Kinetic Study of the Atmospheric Cl Atom-Initiated Oxidation of Propene and a Series of 3-Halopropenes at Room Temperature     

José Albaladejo  Alberto Notario  Carlos A. Cuevas  Bernabé Ballesteros  Ernesto Martínez 《Journal of Atmospheric Chemistry》2003,45(1):35-50

Absolute rate coefficient measurements have been carried out for the reactions of Cl atoms with propene and a series of 3-halopropenes, at room temperature (298 ± 2) K using a newly constructed laser photolysis-resonance fluorescence (PLP-RF) system. The rate coefficients obtained (in units of cm³ molecule^–1 s^–1) are: propene (1.40± 0.24) ×10^–10, 3-fluoropropene (4.92 ± 0.42) ×10^–11, 3-chloropropene (7.47 ± 1.50) × 10^–11, 3-bromopropene (1.23± 0.14) ×10^–10 and 3-iodopropene (1.29± 0.15) ×10^–10. In order to test this new system, the reactions of Cl atoms with acetone and isoprene have also been studied and compared with data previously reported. The rate coefficients determined at room temperature for these last two reactions are (2.93 ± 0.20) ×10^–12 cm³ molecule^–1 s^{– 1} and (3.64± 0.20)×10^–10 cm³ molecule^–1 s^–1, respectively. The measured values were independent of pressure over the range 20–200 Torr. The influence of the different halogen atoms substituents on the reactivity of these alkenes with Cl atoms as well as the atmospheric implications of these measurements are studied and discussed for the first time in this work and compared with the reactivity with NO₃ and OH radicals.  相似文献   

Torsional response of symmetric buildings to incoherent and phase‐delayed earthquake ground motion     

Ernesto Heredia‐Zavoni  Adrin Leyva 《地震工程与结构动力学》2003,32(7):1021-1038

This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three‐dimensional, multi‐storey, multi‐span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase‐delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Oil spill fishery impact assessment modeling: The fisheries recruitment problem     

Mark Reed  Malcolm L. Spaulding  Ernesto Lorda  Henry Walker  Saul B. Saila 《Estuarine, Coastal and Shelf Science》1984,19(6):591-610

A model to assess the impact of oil spill on fisheries, consisting of an oil spill fates model, a continental shelf hydrodynamics model, an ichthyoplankton transport and fates model, and a fish population model, has been applied to the Georges Bank-Gulf of Maine region to estimate the impact of oil spills on several important commercial fisheries. The model addresses direct impacts of oil on a fishery through hydrocarbon-induced egg and larval mortality. This early life stage mortality is estimated by dynamically mapping the spatial intersection of the surface and subsurface oil concentrations resulting from the spill with the developing eggs and larvae. Ichthyoplankton entering an area with hydrocarbon concentrations in excess of a specified threshold are assumed lost. Model output is given in terms of differential catch, comparing the non-impacted and the hydrocarbon impacted fisheries. Difficulties in establishing stock-recruit relationships, and the inability to predict first year survival even one year ahead make the quantification of absolute catch losses impossible. Output of the model system discussed here is therefore limited to relative rather than absolute catch losses.The paper is organized to demonstrate first the importance of the recruitment question to impact estimation, second that a modeling methodology is necessary to evaluate impacts given the magnitude of unexplained observed recruitment variability, and third a stochastic solution to the problem which places impact estimates in the context of a probability distribution. Lastly, the model system is applied to the problem of attaining better early life history mortality estimates, to ultimately improve impact estimation capabilities.  相似文献   

Trophic structure and flows of energy in the Huizache–Caimanero lagoon complex on the Pacific coast of Mexico     

Manuel J. Zetina-Rejn  Francisco Arreguín-Snchez  Ernesto A. Chvez 《Estuarine, Coastal and Shelf Science》2003,57(5-6):803-815

The Huizache–Caimanero coastal lagoon complex on the Pacific coast of Mexico supports an important shrimp fishery and is one of the most productive systems in catch per unit area of this resource. Four other less important fish groups are also exploited. In this study, we integrated the available information of the system into a mass-balance trophic model to describe the ecosystem structure and flows of energy using the E approach. The model includes 26 functional groups consisting of 15 fish groups, seven invertebrate groups, macrophytes, phytoplankton, and a detritus group. The resulting model was consistent as indicated by the output parameters. According to the overall pedigree index (0.75), which measures the quality of the input data on a scale from 0 to 1, it is a high quality model. Results indicate that zooplankton, microcrustaceans, and polychaetes are the principal link between trophic level (TL) one (primary producers and detritus) and consumers of higher TLs. Most production from macrophytes flows to detritus, and phytoplankton production is incorporated into the food web by zooplankton. Half of the flow from TL one to the next level come from detritus, which is an important energy source not only for several groups in the ecosystem but also for fisheries, as shown by mixed trophic impacts. The Huizache–Caimanero complex has the typical structure of tropical coastal lagoons and estuaries. The TL of consumers ranges from 2.0 to 3.6 because most groups are composed of juveniles, which use the lagoons as a nursery or protection area. Most energy flows were found in the lower part of the trophic web.  相似文献   

Retracking of Jason-1 Data   总被引：1，自引：0，他引：1  

Philip S. Callahan  Ernesto Rodriguez 《Marine Geodesy》2004,27(3):391-407

We present the results of retracking 18 cycles (15 from the Jason-TOPEX collinear period) of Jason-1 data. We used the retracking method of Rodriguez which simultaneously solves for all relevant waveform parameters using a 26 Gaussian model of the altimeter point target response. We find significant differences from the Jason-1 Project retracking in the key parameters of range and significant wave height (SWH) in the second version of the Project SGDRs. The differences from the Jason-1 data have a strong dependence on off-nadir angle and some dependence on SWH. The dependence of range on SWH is what is called sea state bias. The retracking technique also estimates surface skewness. For Jason-1 with its very clean waveforms we make the first direct estimates of the skewness effect on altimeter data. We believe that the differences found here and thus in overall sea surface height are the result of the standard project processing using a single Gaussian approximation to the Point Target Response (PTR) and not solving simultaneously for off nadir angle. We believe that the relatively large sea state bias errors estimated empirically for Jason-1 during the cal/val phase result from sensitivity of quantities, particularly SWH, in project GDRs to off nadir angle. The TOPEX-Jason-1 bias can be determined only when a full retracking of Jason-1 is done for the collinear period.  相似文献