Land use dynamics in Brazilian La Plata Basin and anthropogenic climate change

The La Plata Basin (LPB) is one of the most important regions for agriculture and livestock production in South America, playing a central role in the world food production and food security. Within its borders is also located the whole Brazilian Pantanal region. Identifying the most important land use sectors in LPB as well as the changes observed in the past years is fundamental to recognize which areas of the basin might be more vulnerable to climate change in order to design adaptation strategies. A general characterization of land use and livestock production of Brazilian LPB was done by using the System of Automatic Retrieving (SIDRA) of Brazilian Institute of Geography and Statistics (IBGE) platform as the major source of data. It was observed expressive increases in land areas used for temporary crops, such as soybean, sugarcane, and maize, as well as increases in poultry and swine production. These important changes in agricultural land use and livestock production are currently associated to non-climatic drivers, but this dynamic might be strongly affected by the consequences of climate change and variability, with negative socio-economic impacts for the whole region.     

A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing

A potential zircon reference material (BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm³) from Sri Lanka was studied. Within‐grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g^?1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 10¹⁸ g^?1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA‐ICP‐MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW).     

Supercell simulations with simple ice parameterization

Summary A three-dimensional cloud model derived from the Klemp-Wilhelmson model has been used to perform simulations of a right-moving supercell with the purpose of testing the effects of terminal velocity of precipitation on the storm dynamics. The model has no ice variables and computes a fall velocity for condensed water. We simulate one of the effects of ice presence, without including phase transition, by reducing the fall velocity of the precipitation in the coldest cloud layers. The reduction of precipitation terminal velocity is shown to have a strong influence on supercell dynamics and to be responsible for nearly all the improvements in the simulation of supercells that are obtained with full ice microphysics. This includes the transition to tornadic phase, which is sharper than in the case of a pure rain supercell. The vertical component of vorticity is seen to increase at all levels, as observed in real storms, instead of just at the surface as is common in simulations with no ice phase.Our results indicate the primary importance of terminal fall speed among the effects due to the presence of ice.With 13 Figures     

Formulation of a Semi-Geostrophic Model of Frontal Interaction with Isolated Orography

Summary  A semi-geostrophic model of frontal passage over topography was developed to examine the effects of the interaction of a well developed front with an isolated mountain, and the subsequent orographically induced flow evolution. The analytic representation of the primary wave and its frontal structure gives us the ability to control the environmental and geometrical constraints and perform an exploration of parameter space. A number of problems appearing because of this approach are discussed. The results shown relate the characteristics of the orographic perturbation to varying amplitude of the primary wave and varying frontal intensity, but suggest that the representation of flow blocking by the mountain,which this model lacks, is crucial for the representation of frontal intensification in the lee of orography. Received March 2, 1999/Revised May 7, 1999     

Raman and infrared study of hydroxyl sites in natural uvite,fluor-uvite,magnesio-foitite,dravite and elbaite tourmalines

We present the Raman and infrared spectra of different tourmaline species in the spectral range associated with the hydroxyl stretching modes, investigated through polarized Raman spectroscopy. Different lineshapes are observed for the OH spectra in uvite, fluor-uvite, magnesio-foitite, dravite and elbaite samples, and can be related to the coordination of OH in the two different structural V[O(3)]- and W[O(1)]-occupied sites. Local arrangements around the two different OH sites were assigned, and different ion substitutions for these five tourmaline species were identified. Our work with polarized Raman spectroscopy revealed that OH-stretching modes are described by totally symmetric, irreducible representations.     

Environmental forcings and micro-seismic monitoring in a rock wall prone to fall during the 2018 Buran winter storm

Natural Hazards - This study reports a comparative analysis of the environmental conditions and micro-seismicity recorded on a rock wall resulting from an intense meteorological event. The...     

Quasi-stationary organized convection in the presence of an inversion near the surface: Experiments with a 2-D numerical model

Summary Quasi-steady states of organized convection are studied in a two-dimensional nonhydrostatic primitive-equation numerical model. Uni-and multi-cellular patterns are identified in the presence of a low-level inversion, and discussed in relation to those obtained, by various authors, in the more traditional monotonic-sounding case. The stable layer near the ground is shown to be responsible for a configuration of flow normally not observed in cases of monotonic sounding and reminiscent of an orographically generated wave. Exploring the conditions conducive to quasi-steady convection it is found that in the presence of a low-level inversion, a strong shear of the wind component perpendicular to the squall line is required near the surface, deeper than that required in the absence of the inversion.With 10 Figures     

Linear baroclinic instability in the presence of heat inflow from the lower boundary

A linear Eady model with a parameterization of heat influx from the lower boundary is studied analytically in order to obtain the characteristics of baroclinic normal modes modified by this non-adiabatic source. The results display a secondary maximum of growth rate at high wave numbers and a range of absolutely unstable waves, thus suggesting that the property observed among mid-latitude explosive cyclones of being near-stationary in the phase of maximum growth may be captured by this representation of the air-sea energy exchange.     

Validation of a limited area model in cases of mediterranean cyclogenesis: Surface fields and precipitation scores

Summary We have examined the performance of a limited-area mesoscale model of our design in cases of winter cyclones over the southern European-central Mediterranean area with particular ticular attention to standard precipitation statistical scores (bias, threat score, false alarms), obtaining results which compare favourably with other state-of-the-art LAM's documented in the literature. The model, which we briefly describe here, uses standard procedures and includes Geleyn's radiation package and Emanuel's moist convective adjustment scheme. We also discuss the model's performance from the viewpoint of individual surface fields, which display a variety of-mesoscale features correctly reproducing, in most cases, those of the observed fields. The latter have been re-analyzed for this purpose using conventional SYNOP data and ECMWF analyses as first guess.With 18 Figures