Enhancements of CO and O3 from burnings in sugar cane fields

The manual harvest of sugar cane requires the burning of its foliage. This burning has strongly increased in Brazil after the National Alcohol Program was started which substituted automobile gasoline engines for alcohol engines. Presently, the source strength per unit area of this rural pollution is comparable to the well-known biomass burning source in Amazonia. The observed concentrations of CO and O₃ in the rural area of the state of São Paulo during the 1988 burning season were twice as large as those reported from an aircraft experiment of 1985 for biomass burnings of the tropical rain forest. Results are reported from airplane measurements and from three fixed ground stations. Mixing ratios of ozone and carbon monoxide in the height range below 6 km are normally less than 40 and 100 ppbv, (parts per billion by volume), respectively, in the absence of burnings. A strong O₃ and CO layer was observed during the burning period with peak concentrations of 80 ppbv of ozone and 580 ppbv of CO at about 2 km. The concentrations of CH₄ and CO₂ were also large, 1756 ppbv and 409 ppmv, respectively, at 1500 m. During the dry season period of the experiment, the ground based O₃ average diurnal variations obtained at the rural sites were practically identical to the typical urban variation observed at São José dos Campos, with daytime ozone values between 45 and 60 ppbv. A second three-day airplane excursion to the surgar cane fields in the wet season of 1989 has produces results to be contrasted with the dry (burning) season of 1988 and 1989. Carbon monoxide concentrations were below 100 ppbv at all heights and ozone concentrations were around 30–40 ppbv. The maximum daytime concentrations at the ground station Bauru was 25 ppbv of O₃, and at Jaboticabal it was 35 ppbv of O₃, only one half of what was observed in the dry season.Universidade Estadual de São Paulo.     

Characterization of dissolved organic materials in surface waters within the blast zone of Mount St Helens,Washington

After the May 18, 1980, eruption of Mount St Helens, the concentration of dissolved organic material in surface waters near the volcano increased significantly as a result of the destruction of the surrounding conifer forest. Low molecular weight organic compounds identified in the blast zone surface waters were derived from pyrolysis of plant and soil organic materials incorporated into pyroclastic flow, mud flow and debris avalanche deposits. A major fraction of the dissolved organic material consisted of high molecular weight, colored, organic acids that are similar in their general properties to aquatic fulvic acids found in more typical surface waters except for greater sulfur contents. The other major fraction of the dissolved organic material consisted of hydrophilic acids, which may include compounds capable of supporting heterotrophic microorganisms, and precursors in the formation of aquatic fulvic acids. The organic chemistry of blast zone surface waters will probably be greatly influenced by the May 18, 1980, eruption for many years.     

Assessment and compensation of inconsistent coupling conditions in point-receiver land seismic data

We introduce a method to detect and compensate for inconsistent coupling conditions that arise during onshore seismic data acquisitions. The reflected seismic signals, the surface waves, or the ambient-noise records can be used for the evaluation of the different coupling conditions of closely spaced geophones. We derive frequency-dependent correction operators using a parametric approach based upon a simple model of the interaction between geophone and soil. The redundancy of the measurements available permits verification of the assumptions made on the input signals in order to derive the method and to assess the validity of the model used. The method requires point-receiver data in which the signals recorded by the individual geophones are digitized. We have verified the accuracy of the method by applying it to multicomponent ambient-noise records acquired during a field experiment in which the coupling conditions were controlled and modified during different phases of the experiment. We also applied the method to field data, which were acquired without the coupling conditions being controlled, and found that only a few geophones showed an anomalous behaviour. It was also found that the length of the noise records routinely acquired during commercial surveys is too short to provide enough statistics for the application of our method.     

Geographic variations in shell growth rates of the mussel Diplodon chilensis from temperate lakes of Chile: Implications for biodiversity conservation

The Chilean lake district includes diverse lentic ecosystems along ca. 700 km of the country (36°–43°S), including the “Nahuelbutan lakes”, “Araucanian lakes” and “Chiloe lakes”. This area is recognized as an important “hot spot” of benthic freshwater biodiversity in Southern South America. In Chilean temperate lakes, increased nutrient loads of P and N caused eutrophication, particularly in the Nahuelbutan Lakes. The freshwater Hyriidae mussel Diplodon chilensis (Gray, 1828) which is one of the most abundant species in Chilean temperate lakes, is known to be very susceptible to eutrophication. This species presents a clear reduction in its geographic ranges and is considered to be a threatened species in many Chilean lakes. In this study, we used a correlative approach to determine how eutrophication-driven changes in the food supply and in geographical parameters of different Chilean lakes affected the shell growth rates of D. chilensis. The results obtained from sclerochronological analyses of the mussel shells suggest an association with a group of environmental variables, including geographical types (negative), such as latitude and altitude, and limnological types (positive), especially phosphorous and turbidity. However, the D. chilensis populations under extreme conditions of turbidity in eutrophic and hypertrophic lakes are extinct or nearly so. The high positive correlation of the mean D. chilensis growth rates with orthophosphate (R=0.76; P<0.05), in relation to dissolved inorganic nitrogen, suggests that P is the major limiting factor of the primary productivity in Chilean temperate lakes. We discuss some implications of our results in terms of the conservation of biodiversity in temperate lake ecosystems at different taxonomic levels.     

Mapping and initial dilution estimation of an ocean outfall plume using an autonomous underwater vehicle

A monitoring mission to study the shape and estimate initial dilution of the S. Jacinto outfall plume using an autonomous underwater vehicle (AUV) was performed on July 30, 2002. In order to reduce the uncertainty about plume location and to concentrate the vehicle mission only in the hydrodynamic mixing zone, outputs of a near-field prediction model, based on effective real-time in situ measurements of current speed and direction and density stratification, were opportunistically used to specify in real time the mission transects. The surface characteristics of the outfall plume were found to be influenced strongly by the relatively weak stratification and low current velocities. Dilution was estimated using a temperature–salinity (TS-) diagram with initial mixing lines between wastewater and ambient waters. Effluent dilutions were at least 30:1 in this study. In order to efficiently map the plume dispersion we applied the least-squares collocation method technique. Our results demonstrate that AUVs can provide high-quality measurements of physical properties of effluent plumes in a quite effective manner and valuable considerations about the initial mixing processes under real oceanic conditions can be further investigated.     

Modelling of ground motion in the vicinity of massive structures

A two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturcture's mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q < 15).The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the ‘free-field’ ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings.     

Numerical study of non-linear storm-surges

Summary The problem of storm-surges is investigated in a rectangular basin, setting up a numerical hydrodynamical model using the shallow-water equations. The forcing exerted by the atmosphere is given in the idealized form of a constant wind blowing over a section of the basin. The case in which the window of wind is moving is considered and for a basin that has the same dimensions of the Adriatic Sea. The conditions that give the maximum surge at one edge of the basin are investigated.

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Riassunto Il problema relativo alle storm-surges viene studiato in un bacino rettangolare, costru endo un modello idrodinamico numerico ed usando le equazioni relative ad acqua poco profonda. Lo stress esercitato dall'atmosfera è dato nella forma idealizzata di un vento costante che soffia sopra una sezione del bacino. Si considera il caso in cui la finestra di vento è in moto e per un bacino che ha le medesime dimensioni del mare Adriatico. Si studiano le condizioni che provocano il massimo dell'innalzamento ad un estremo del bacino.

     

Nonlinear wave coupling in type IV solar radio bursts

In order to explain a fine structure of parallel ridges in stationary type IV continua, the emission due to the coupling of electrostatic upper hybrid waves and Bernstein waves at the sum frequency of the upper hybrid and harmonics of the gyro frequency has been calculated. If the energy density of these electrostatic waves is of the order of 10^-3 times the thermal energy density, then the observed zebra pattern can be emitted by a region with a diameter of 10³ km.     

Multi-offset phase analysis of surface wave data (MOPA)

Inaccuracy in the shear wave velocity profile inverted from surface wave data manifests from both modelling error and data uncertainty. An alternative method for dispersion curve evaluation by weighted linear regression of phase-offset data can be applied to both equispaced and non-equispaced data for objective identification of these often overlooked error sources.From field data, near-field effects are noted to at most half a wavelength and lateral discontinuities identified by marked changes in wavenumber with offset. Transition frequencies to dominant higher modes appear lower than when identified from standard plane-wave transform methods. Effects can be discriminated by their frequency, position or offset dependence.When a non-corrupt dispersion curve is extracted, the errors are up to 5% at low frequency. Through theoretical Gaussian error propagation analysis, the resulting shear wave velocity profile shows up to 18% uncertainty at depth.     

Multi-year drought frequency analysis at multiple sites by operational hydrology - A comparison of methods

This paper compares two generators of yearly water availabilities from sources located at multiple sites with regard to their ability to reproduce the characteristics of historical critical periods and to provide reliable results in terms of the return period of critical sequences of different length. The two models are a novel multi-site Markov mixture model explicitly accounting for drought occurrences and a multivariate ARMA. In the case of the multisite Markov mixture model parameter estimation is limited to a search in the parameter space guided by the value of parameter λ to show the sensitivity of the model to this parameter. Application to two of the longest time series of streamflows available in Sicily (Italy) shows that the models can provide quite different results in terms of estimated return periods of historic droughts, although they seem to perform more uniformly when it comes to simulate drought-related statistics such as drought length, severity and intensity. The role of parameter selection for the multisite Markov mixture model and of the marginal probability of generated flows in providing results consistent with the characteristics of the observed series is discussed. Both models are applied to the system of sources supplying the city of Palermo (Sicily) and its environs showing the applicability of the newly developed multisite Markov mixture model to medium-to-large scale water resources systems.