Atmósfera (Journal)
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Sensitivity of Loop Current metrics and eddy detachments to different model configurations: The impact of topography and Caribbean perturbations
Get PDFThe dynamics of the Loop Current (LC) and the release of its anticyclonic eddy (Loop Current eddy, LCE) are some of the most important features of the circulation in the Gulf of Mexico (GoM) and key aspects to gauge the validity of numerical simulations. Using a numerical model, we investigate the sensitivity of the LC and LCE detachments to three different mechanisms deemed to be relevant to their behavior: a) suppression of Caribbean vorticity perturbations entering the GoM; b) smoothness of the topography, and c) suppression of a deep canyon on the eastern Campeche Bank.The main results of these experiments in comparison to a reference run considered to be the more realistic one are:a. Suppression of Caribbean eddies reduces the number of LCE separations, but they are not the principal mechanism that triggers the separations. Locally generated instabilities over the northeastern Campeche Bank and the LC northward extension, appear to be the controlling factors.b. Smoothing the topography generates a wider and less intense LC and reduces the energy exchange terms related to flow instabilities. Nevertheless, the number of LCE separations is similar to the reference experiment. Extension of the LC controls the shedding that, in this case, tends to occur in the summer-fall season, when the LC is more extended, and the Yucatan transport abruptly weakens after its seasonal maximum.c. Removing the deep canyon in the eastern Campeche Bank, makes the LC extension more stable and reduces the number of LCE separations. The canyon appears to play an important role in spinning up cyclones generated over the LC eastern front that finally leads to an LCE release.The seasonal distribution of LCE separations in the experiments does not appear to be controlled by the strength of the barotropic and baroclinic instability source terms. Instead, a necessary but not sufficient condition for LCE separations is that the LC extends beyond 24º N. Our results indicate that caution should be exercised when interpreting LC statistics from a single numerical configuration
Study of vehicle emissions between Neuquén and Centenario, Argentina
Get PDFVehicle traffic and its effects on air quality were analyzed on the surroundings of provincial route No. 7 between the cities of Neuquén and Centenario. Concentration levels of carbon monoxide, nitrogen oxides and sulfur dioxide were estimated for a period of five years (2005-2009) through regular data of traffic flow, considering average speeds per sector, the characteristics of vehicles in circulation and meteorological data. Calculations were made by applying CALINE, a line source Gaussian dispersion model developed for predicting pollution levels near highways and arterial streets. In the cases analyzed within the area of study, critical concentrations of gases did not exceed the limits established by Argentinean regulations nor current international standards. The results describe the impacts on receptors located near the route in areas that comprise both industrial and agricultural activities. The route analyzed presents high vehicular traffic with more than 14 000 vehicles traveling daily during 2007. Within a five-yr period, daily traffic increased by 12%. The study revealed that the highest concentration of gases occurred during the winter season in morning hours, when vehicles decreased their velocity at a toll area. This situation may have been modified in behalf of air quality due to the removal of the toll station
Flood frequency analysis using synthetic samples
Get PDFThe design flow is the basis for planning and designing different hydraulic works. The precision in estimated flows is important when analyzing the feasibility of such structures because the value directly influences the evaluation of the failure effects. However, due to flow variability, the precision of the estimate is drastically reduced when small samples are used in a conventional flood frequency analysis (FFA). This paper proposes a new approach based on a combined simulation of the annual peak and mean flows. The method was evaluated by considering 10-, 20-, 30-, 40- and 50-yr subsamples obtained from 13 gauging stations located in the Susquehanna River basin. The results were compared with those obtained by FFA and the regional station-year method. This new approach can reduce the uncertainty in estimating the design flow when few data are available
Estimated carbon dioxide exchange for three native species in an ecological reserve of Mexico City
Get PDFCapture and emission of carbon dioxide of three species (Buddleia cordata, Senecio praecox and Echeveria gibbiflora) in the Reserva Ecológica del Pedregal de San Ángel (Ecological Reserve of the Pedregal de San Ángel), were estimated. CO2 sampling was carried out in 2010 during the dry (February, March, April and November) and rainy seasons (July to October). On the dry season B. cordata and S. praecox captured 16.14 and 3.25 kg CO2, respectively, whereas E. gibbiflora emitted 45.76 kg CO2. In the rainy season the exchange of CO2 was different for the three species. In the dry season, the photosynthetic rate was 22 pmol CO2 m–2 s–1 for B. cordata, 27 pmolCO2 m–2 s–1 for S. praecox and 29 pmolCO2 m–2 s–1 for E. gibbiflora. In the rainy season they were 6, 5.25 and 3 pmol CO2 m–2 s–1, respectively. In addition, MODIS data were used to estimate the normalized difference vegetation index (NDVI), indicating that the intensity of greenery at the site increased during the rainy months. This paper explains the contribution of studied plants to the carbon cycle of an ecosystem located within an urban area, and the relationship of environmental variables such as temperature, density photosynthetic photon flux and relative humidity in the capture or emission of CO2. This work provides valuable information about the carbon cycle dynamics on urban ecosystems, which can be useful in future studies for climate change mitigation
Intercomparison of improved satellite rainfall estimation with CHIRPS gridded product and rain gauge data over Venezuela
Get PDFSatellite-derived rainfall products are useful for both drought and environmental monitoring, and they also allow for tackling the problem of sparse, unevenly distributed and erratic rain gauge observations provided their accuracy is well known. Venezuela is a country highly vulnerable to extreme weather events such as extensive droughts and flash floods; therefore, an understanding of the strengths and weaknesses of satellite-based rainfall products is useful for the planning of water resources. Using numerical metrics in order to evaluate performance, monthly rainfall estimates, from the Climate Hazards Group InfraRed Precipitation and Stations (CHIRPS v.2) product, are compared to gauge data from the 1981-2007 interval and categorical metrics for assessing rain-detection skills. The analysis was performed considering different rainfall categories, seasonality, and spatial context. The results show that the satellite product CHIRPS v.2 overestimates (underestimates) low (high) monthly rainfall values; although on the majority of numerical metrics of skill shows a good performance. This product, on the other hand, achieves better performance during the rainy season (April-September), significantly overestimating, however, the rainfall-events frequency. The product also shows best overall performance over flat and open regions (e.g., Los Llanos), where precipitation is influenced by the Intertropical Convergence Zone activity and local convective systems
Wind tunnel simulations to detect and quantify the turbulent effects of a propagating He-Ne laser beam in air
Get PDFIn this paper, we ascertain the effectiveness of our experimental setup in detecting and quantifying the turbulent effects experienced by a He-Ne laser beam as it passes through a wind tunnel. The beam propagated through a series of optical components as well as the in-house designed and manufactured wind tunnel under controlled laboratory conditions. The wind tunnel was built to fit within an existing setup, which has previously proven to be successful in detecting the turbulent effects from other turbulence models. For various wind speeds and temperature settings, the setup has been successful as it was able to detect and measure the atmospheric conditions within the turbulent environment and fully quantify the characteristics of the laser beam. With the use of highly accurate measuring devices, we were able to successfully measure the refractive index structure function (Cn2) and the coherence diameter (Fried’s parameter). Values for Cn2 ranged between 1.61 × 10–16 m–2/3 and 6.77 × 10–15 m–2/3, which can be classified under the moderate to strong turbulence regime. These results tie in well with various published works for similar atmospheric scenarios hence this setup was successfully able to fully detect and quantify the thermal turbulence and wind velocity effects on the laser beam using a point diffraction interferometer
Climate patterns of political division units obtained using automatic classification trees
Get PDFThis article proposes a methodology to discover patterns in observed climatologic data, particularly temperatures and rainfall, in subnational political division units using an automatic classification algorithm (a decision tree produced by the C4.5 algorithm). Thus, the patterns represent classification trees, assuming that: (1) every political division unit contains at least one climatological station, and (2) the recording periods of the stations are relatively similar in duration and in their initial and ending years. A series of classification models are produced by using different subsets from an experimental dataset. This dataset contains information from 3606 climatological stations in Mexico with recording periods whose durations, initial and ending years are diverse. The target (dependent) variable in all these models is the name of the political unit (i.e., the state). The predictors are 36 monthly features per each climatological station: 12 features corresponding to a minimum temperature, 12 to a maximum temperature, and 12 to cumulative rainfall. The altitude feature is also used as one of the predictors, in addition to the other 36; however, it is used only to quantify its additional contribution to the modelling. The results show that classification trees are effective models for describing and representing non-trivial patterns to characterize the political division units based on their monthly temperatures and rainfalls. One of the remarkable findings is that the cumulative rainfall of May is the feature with highest discrimination capability to the characterization task, which is consistent with the theoretical background on Mexican climatology. In addition, classification trees offer higher expressivity to non-experts in machine learning
Indoor PM10 and its heavy metal composition at a roadside residential environment, Phitsanulok, Thailand
Get PDFThe concentrations of PM10 were measured both indoors and outdoors at 10 roadside residential buildings in Phitsanulok, Thailand during the dry and wet seasons of 2014. Seven trace metals (Zn, Fe, Pb, Cd, Ni, Cu and Cr) were also analysed in PM10. The monthly average concentrations of indoor and outdoor PM10 were 41.5 to 105.3 μg m–3 and 95.2 to 145.1 μg m–3, respectively. PM10 concentrations were significantly higher during the dry season compared to the wet season. The indoor/outdoor (I/O) ratios were less than one indicating that the particulate matter originates from the outdoor environment. Overall, the average concentrations of heavy metals in PM10 ranged from 0.2 to 2.7 μg m–3 and 0.5 to 7.1 μg m–3 for the indoor and outdoor environments, respectively. A strong positive correlation in indoor PM10 was found between Zn and Cu, Zn and Ni, and Cu and Ni. Zn and Ni, Pb and Cu, Cu and Ni, Cd and Ni, and Zn and Cu showed strong positive correlations in the outdoor environment. The enrichment factors of Zn, Cu, Pb, Cr and Ni were less than one suggesting that the metals in indoor PM10 have originated from crustal materials. For the health risk assessment, Cr was found to have the highest excess cancer risk in an evaluation using an Integrated Risk Information System
Effects of soil heat storage and phase shift correction on energy balance closure of paddy fields
Get PDFThe eddy covariance technique was used to measure the energy fluxes of a paddy field under water-saving irrigation in the South China Plain for the stage of rice growth in 2013. This study analyzed the energy balance components and evaluated the energy balance closure. The study also discussed the response of surface energy balance to the change in soil heat storage between the heat flux plates buried at a specific depth and the surface, and the phase shift correction of energy balance components, by using three different statistical methods, namely ordinary least squares (OLS), energy balance ratio (EBR), and energy balance residual (D). The results showed that the OLS slope increased by an average of 8.8%, and the mean daily EBR increased by 5.0% after considering the change in soil heat storage. The range of half-hourly D over a four-month period decreased from –129 - 260 W m−2 to –102 - 194 W m−2, and the absolute value of D decreased by 9.9% on the average. Considering the phase correction, the increase in OLS regression coefficients with an average of 11.3% and the decrease in half-hourly D, ranging from –61 to 176 W m−2, both indicated that phase shift correction improved the surface energy balance closure at the half-hourly scale, specifically in the period from sunrise to noon, but had no use in the daily scale. Thus, the two correction methods are useful in improving the degree of energy balance closure shown in different temporal scales with proper evaluation index. Moreover, further research should be given with more attention for other correction aspects
High resolution satellite derived erodibility factors for WRF/Chem windblown dust simulations in Argentina
Get PDFA proper representation of dust sources is critical to accurately predict atmospheric particle concentration in regional windblown dust simulations. The Weather Research and Forecasting model with Chemistry (WRF/Chem) includes a topographic-based erodibility map originally conceived for global scale modeling, which fails to identify the geographical location of dust sources in many regions of Argentina. Therefore, this study aims at developing a method to obtain a high-resolution erodibility map suitable for regional or local scale modeling using WRF/Chem. We present two independent approaches based on global methods to estimate soil erodibility using satellite retrievals, i.e. topography from the Shuttle Radar Topography Mission (SRTM) and surface reflectance from the Moderate Resolution Imaging Spectroradiometer (MODIS). Simulation results of a severe Zonda wind episode in the arid central-west Argentina serve as bases for the analysis of these methods. Simulated dust concentration at surface level is compared with particulate matter measurements at one site in Mendoza city. In addition, we use satellite aerosol optical depth (AOD) retrievals to investigate model performance in reproducing spatial distribution of dust emissions. The erodibility map based on surface reflectance from MODIS improves the representation of small scale features, and increases the overall dust aerosol loading with respect to the standard map included by default. Simulated concentrations are in good agreement with measurements as well as satellite derived dust spatial distribution