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Eastern Iberian Peninsula is characterized by the large occurrence of convective precipitation events, which entail important economic and social damage consequences. In order to prevent and minimize its effects, a good knowledge ...
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Eastern Iberian Peninsula is characterized by the large occurrence of convective precipitation events, which entail important economic and social damage consequences. In order to prevent and minimize its effects, a good knowledge and understanding of the meteorological processes involved are necessary to be achieved. In this regard, an algorithm for classifying convective and stratiform precipitation components has been applied to a decadal precipitation record. Dataset were provided by National Spanish Meteorological Agency (AEMET) for the period 1998-2008. Hourly precipitation records have been analyzed. The goals of this study have been: a) to classify total precipitation into its stratiform and convective components in Levante region (located in the Eastern Spanish Coast) and b) to analyze annual and seasonal trends of such components. For determining both convective and stratiform precipitation components, a suitable exponential function has been used. After a computation process, critical precipitation intensity (so-called Rc) is obtained for each year and season of the studied period. Every precipitation episode in Levante region is classified into prevailing convective or stratiform regime according to the threshold value defined by Rc. The results obtained have been compared to Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) to verify the validity of the algorithm. First results show an annual and seasonal significant positive trend in total precipitation and stratiform component for 1998-2008 decade. Further analysis reveals that convective precipitation exhibits no significant trend. Preliminary conclusions state that the total precipitation amount in Levante Region strongly depends on the stratiform component evolution.
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A new index assessing the cloud growing rate isdescribed in this paper. It has been designed to be integratedin rainfall estimation procedures. As the highestprecipitation rates occur in growing convective cores,integrating this i...
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A new index assessing the cloud growing rate isdescribed in this paper. It has been designed to be integratedin rainfall estimation procedures. As the highestprecipitation rates occur in growing convective cores,integrating this information should enhance theprecipitation estimations. The index computation relies onimage processing methods. It is composed of two steps: firsta watershed segmentation is applied and then an originalheritage process is performed. This second step, which isbased on a simple matrix computation, is adapted to thewatershed algorithm as it mitigates the over-segmentationartefact. This cloud growing rate index is compared with acooling index which is usually computed to help inidentifying raining cells and it is demonstrated to be moreefficient. Moreover a simple integration of this index ina widespread rainfall estimation method leads to animprovement of the diurnal cycle retrieval
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Drylands occupy about 41% of land surface and feed 38% of the world's population, where understanding drylands' water-cycle is in urgent need. In this study, response of water-cycle over the drylands to global warming from 1980 to...
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Drylands occupy about 41% of land surface and feed 38% of the world's population, where understanding drylands' water-cycle is in urgent need. In this study, response of water-cycle over the drylands to global warming from 1980 to 2015 and its mechanisms have been investigated in detail. The results show that, with the global surface air temperature (SAT) increasing at a rate of 0.03 K.year(-1) over the drylands, an increased evaporation is found; however, the net water vapour transport over the global drylands appears an overall decreased rate of -0.24 mm.year(-1). Due to global warming and atmospheric circulation anomalies, the evaporation increases by 1.1 mm.year(-1), while the precipitation and runoff decrease by -2.32 and -0.8 mm.year(-1), respectively. In addition, the precipitation conversion rate (PCR) tends to decrease during this period, while the precipitation recycling rate (PRR) shows slightly increasing trend, implying a more dependence of the precipitation on the local evaporation over the drylands. Overall, except the drylands of Africa, it indicates a weakened water-cycle over the global drylands from 1980 to 2015. Though some findings have been revealed, there still remains some uncertainties due to the observation limitation on the water-cycle components. Therefore, a comprehensive study including multi-sourced data and model simulation is expected in the future.
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A relation between template properties and template performance has been established: template particles with a surface layer of cinnamic acid molecules, either adsorbed or covalently bonded, promote crystallization of cinnamic ac...
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A relation between template properties and template performance has been established: template particles with a surface layer of cinnamic acid molecules, either adsorbed or covalently bonded, promote crystallization of cinnamic acid, while particles without such a layer do not. The BET surface area and dynamic light scattering (DLS) particle size were measured to gain control over the total surface area of added template particles (ZrO2, TiO2, TiO2-SiO2, and SiO2-CAH). Zeta-potential measurements indicated whether adsorption of cinnamate on particles occurred, while the loading of the surface layer with cinnamic acid molecules was determined by adsorption isotherm measurements and spectrophotometry. The template performance was evaluated using induction time measurements. Scanning electron microscopy (SEM) images revealed that effective templates not only improve nucleation rates, but may also affect the size and shape of crystals. Template induced crystallization (TIC), where template particles promote crystallization, can be used as an in-situ product removal (ISPR) tool in fermentation processes to alleviate inhibitory and/or toxic constraints which are due to high product titers. The established relation between template properties and template performance can be used to predict which materials are effective templates for a specific (fermentation) product.
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Attica, which is the region with the largest population in Greece, suffers from numerous high rainfall intensity events inducing flash floods and, consequently, significant damages in the urbanized areas. High rainfall intensities...
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Attica, which is the region with the largest population in Greece, suffers from numerous high rainfall intensity events inducing flash floods and, consequently, significant damages in the urbanized areas. High rainfall intensities are frequently connected with convection, a quiet often phenomenon during either the transitional seasons or the late summer thunderstorms. The objective of this paper is to implement and evaluate a stratiform-convective classification technique for the rainfall events occurred in Attica during the period 2005-2016. As this methodology requires only the precipitation records, the satisfactory evaluation of this classification approach allows further applications, such as, a climatological analysis regarding convective and stratiform trends in the study area and generally in Greece. Particularly, the rain gauge stations' records used correspond to 10 minute time series from 32 rainfall stations for the same period, and these data are analyzed and processed in order to fit a suitable exponential curve describing the stratiform component. A critical annual threshold of rainfall intensity in mm/6h is then calculated, separating the prevailing convective and stratiform regime above and below this value, respectively. The analysis is performed in three individual subareas of Attica region demarcated initially according to their morphological characteristics and subsequently by checking the cross correlation for each pair of stations. This critical intensity threshold is determined for each year separately, in order to illustrate the uncertainty and the difficulty in identifying a standard threshold, as it is related to the annual behavior of precipitation. Using this threshold, a total of about 180 six-hour case events is detected as purely convective cases, however this number ranges for each subarea. For these cases, a further analysis is performed with the aim of verifying their convective character. Verification includes time-accurate lightning data, surface synoptic observations from the Hellenic National Meteorological Service and six-hour surface analysis charts from UK MetOffice. Findings, which are presented via indicative verification indices, show in general encouraging performance, considering the highly variable nature of convective precipitation which poses considerable problems in its identification with quite simple techniques.
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? 2023 Elsevier LtdThis study investigated the influence of natural aging (NA) on the precipitation behavior of the main precipitate β″ and hardness evolution during the subsequent artificial aging (AA) process of the precipitat...
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? 2023 Elsevier LtdThis study investigated the influence of natural aging (NA) on the precipitation behavior of the main precipitate β″ and hardness evolution during the subsequent artificial aging (AA) process of the precipitation strengthened A357 aluminum alloy. The corresponding mechanisms were analyzed. The results demonstrate that natural aging has adverse influence on the precipitation process during artificial aging. The underlying mechanism is that small GP zones are formed during natural aging but cannot become nucleation sites for the β″ phase during artificial aging, which spontaneously consumes the supersaturated solute atoms in the Al matrix, increases the nucleation barrier of the β″ phase, and also consumes the vacancies produced after solid solution and quenching, thereby reducing the nucleation rate of the β″ phase during artificial aging, and leading to an un-expected increase in the size of the precipitated phase, thus reducing the peak aging hardness of the alloy. This effect becomes more pronounced with increasing natural aging time. Increasing the artificial aging temperature can improve the nucleation rate of the β″ phase during artificial aging, thereby to some extent reducing the unfavorable influence of natural aging on the artificial aging by reducing the sizes and increasing the amount of the β″ precipitates.
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Kaolinite was hydrothermally precipitated starting from amorphous aluminosilicates, with Si/Al ratio from 1.8 to 0.76, at temperatures of 150, 175, 200, 225, and 250 deg C, at time periods varying from 6 h to 60 days. The solution...
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Kaolinite was hydrothermally precipitated starting from amorphous aluminosilicates, with Si/Al ratio from 1.8 to 0.76, at temperatures of 150, 175, 200, 225, and 250 deg C, at time periods varying from 6 h to 60 days. The solutions were analysed for pH, Si, Al, and K, and their saturation state was calculated by using the computer program SOLMINEQ.88. The solids were studied by surface area, XRD and DTA-TG analyses. Kaolinite was the only crystalline phase found in the products of the runs and its formation and crystallinity depended on time, temperature, and Si/Al ratio of the starting material. The kaolinite yield increased as starting material was aged for longer times. Products synthesized at higher temperature contain more kaolinite which was more crystalline than in the experiments carried out at lower temperature. The gel with Si/Al = 0.99 produced the most disordered kaolinite and better crystallinity was obtained from products richest in Al or Si. The process of kaolinite formation was the result of two stages. During the first one aggregates of domains having a kaolinite-like structure were formed. The second stage corresponded to the formation of hexagonally outlined platy crystals. The formation rates indicated that the first stage was approximately one order of magnitude faster than the second stage, with average activation energies of 82 +- 5 kJ mol~(-1) and 71 +- 5 kJ mol~(-1), respectively. Si/Al ratio of the starting material exerted only a slight influence on the activation energies. The precipitation rates obtained for the second stage were consistent with literature data and may be considered precipitation rates of kaolinite in hydrothermal environments.
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