Atmósfera (Journal)
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CLIMATE VARIATIONS IN A HIGH ALTITUDE ALPINE BASIN AND THEIR EFFECTS ON A GLACIAL ENVIRONMENT (ITALIAN WESTERN ALPS)
Get PDFThe main objective of this study is to evaluate the variations of climatic parameters (temperature, rain and snow) measured by two weather stations (Formazza and Sabbione) that have never been analyzed before, located in a high glacial catchment (the Sabbione basin in the Italian Western Alps). The study highlights the climatic evolution of the Alpine basin during the last 60 years (1950-2012): climate change has caused a pronounced glacial decline originated by ablation augmentation, due mainly to increasing air temperatures and to reduced alimentation caused by a fresh snow decrease. The cross-correlation test shows that temperatures affect the glacial retreat dynamics more than snowfall. Periglacial and permafrost landforms (e.g., patterned grounds, rock glaciers) have been identified within the Little Ice Age (LIA) glacial deposits, which indicate the ongoing transition from glacial/proglacial to periglacial environments. Furthermore, in order to better identify the periglacial domain in the basin, a map of mean annual air temperature (MAAT) was produced based on climatic analysis.
Exact solutions of the vorticity equation on the sphere as a manifold
Get PDFThe purpose of this paper is to represent the exact solutions of the barotropic vorticity equations (BVE) on the rotating unit sphere S2 as a manifold, which are zonal flows, Rossby-Haurwitz waves and generalized solutions named modons. Modern methods of the function theory are connected to the sphere defined as a compact differentiable manifold. When the differentiable manifold S2 is well understood, the abstract notion of local chart, change of chart, and atlases becomes evident. One of the aims of this paper is to better understand the solution of the barotropic vorticity equation on the manifold S2 and its usefulness to identify the properties of the solutions on the Riemannian manifold (S2, g). Therefore, a more general type of space will be available, which can also contain substantial geometric and analytic information about solutions for the barotropic vorticity equation
Sensitivity of PBL schemes of the WRF-ARW model in simulating the boundary layer flow parameters for their application to air pollution dispersion modeling over a tropical station
No full textMesoscale atmospheric circulations play an important role in the transport of air pollution and local air quality issues. The planetary boundary layer (PBL), the thermo-dynamical structure and the flow field play an important role in air pollution dispersion. Hence, the PBL parameters over Nagpur, India are simulated using the ARW v. 3.6.1 mesoscale model. High-resolution simulations are conducted with triple nested domains having a horizontal resolution of 27, 9 and 3 km, as well as 27 vertical levels by using the 1 . 1º NCEP Final Analysis meteorological fields for initial and boundary conditions. Eight fair-weather days in winter and summer (January and April 2009) with no significant synoptic activity were chosen for the study. Sensitivity experiments of the ARW model were conducted with two non-local (Yonsei University [YSU], and Asymmetric Convective Model v. 2 [ACM2]) and three local turbulence kinetic energy (TKE) closure (Mellor-Yamada Nakanishi and Niino Level 2.5 PBL [MYNN2], Mellor-Yamada-Janjic [MYJ], and quasi-normal scale elimination [QNSE]) turbulence diffusion parameterizations, to study the evolution of PBL parameters and the thermodynamical structure during the study period. After validation of the simulated parameters with the available in-situ data, it was revealed that the non-local PBL scheme YSU, followed by local scheme MYNN2, could able to capture the characteristic variations of surface meteorological variables and the thermodynamical structure of the atmosphere. The present results suggest that the PBL schemes, namely YSU and MYNN2, performed better in representing the boundary-layer parameters and are useful for air pollution dispersion studies
Climate downscaling over South America for present- day climate (1970-1989) using the MM5 Model. Mean, Interannual Variability and Internal Variability
No full textThis work focuses on evaluating the ability of the MM5 regional model to represent the basic features of present climate over South America. The spatial distribution of seasonal means and its interannual variability as well as annual cycles for precipitation and near-surface temperature have been evaluated. The internal variability has also been investigated. The analysis has two objectives, one of them is to quantify the dynamic downscaling ability to represent the current climate and the other identify the critical aspects of the regional climate model in South America in order to interpret future projections for the end of XXI century in the SRES A2 scenario with a degree reliability.In general, the MM5 model is able to adequately reproduce the main general features, the seasonal cycle and the year-to-year variability of surface variables over South America. The spatial distribution of temperature is well represented, but it can be found some systematic errors such as an overestimation in central and northern Argentina and an underestimation in the mountainous regions throughout the year. The general structure of precipitation is also well captured by the regional model, although it overestimates the precipitation in the Andean region (specifically in the central and southern Chile) in all seasons and underestimates the rainfall in tropical latitudes. The annual cycle of precipitation is adequately represented in the subregions analyzed, but its representation is better at La Plata Basin (LPB), Cuyo (CU) and Sureste Pampas (SEP). The annual cycle of mean temperature is well represented, too. The model systematically overestimates the interannual variability of temperature and underestimates the interannual variability of precipitation. From the analyses of interannual, internal variability and biases, it can be conclude that regardless the season, the MM5 regional model precipitation is reliable at subtropical latitudes, Uruguay, southern Brazil and centre east of Argentina but it is unreliable over areas of elevated topography. For temperature the regional model is reliable on subtropical latitudes, Uruguay and south of Brazil only during winter, but it less reliable is or even it is in the limit of reliability over centre and south of Chile along the year.Therefore, it is concluded that the MM5 model is a useful tool in the generation of regional climate change scenarios of high resolution over southern South America and is an interesting starting point to perform others evaluations on climate change studies that are discussed in a companion paper
Modeling methane emissions and methane inventories for cattle production systems in Mexico
Get PDFAnaerobic fermentation of structural carbohydrates in the rumen of bovines produces waste products such as volatile fatty acids, fermentation heat, carbon dioxide and methane gas. Methane is a greenhouse gas having several times the global warming potential of CO2. The purpose of the present paper is to provide a realistic estimate of the national inventory of methane produced by the enteric fermentation of cattle, based on a simulation model and to provide estimates of CH4 produced by cattle fed typical diets from the tropical and temperate climates of Mexico. Predicted total emission of methane produced by the 23.3 million heads of cattle in Mexico is approximately 2.02 Tg/yr. It was concluded that the modeling approach was suitable in producing a better estimate of the national methane inventory for cattle. It is flexible enough to incorporate more cattle groups or classification schemes, productivity levels and a variety feed ingredients for cattle. The model could also be used to evaluate different mitigation strategies and serve as a tool to design mitigation policies.La fermentación anaeróbica de los carbohidratos estructurales en el rumen de los bovinos genera productos de desecho como ácidos grasos volátiles, calor de fermentación, bióxido de carbono y gas metano. Este último es un gas de invernadero que tiene un potencial varias veces mayor que el CO2 para inducir calentamiento global. El objeto del presente trabajo es aportar una estimación del inventario nacional de metano producido por la fermentación entérica del ganado bovino en México, realizado a partir del uso de un modelo matemático de simulación. Se hizo una clara diferenciación entre el CH4 producido por bovinos que consumen una dieta típica de las regiones tropicales y aquellos que se alimentan con ingredientes de las regiones templadas de México. Se estimó que la emisión total de metano producido por las 23.3 millones de cabezas de bovinos de México asciendea aproximadamente 2.02 Tg/año. Se concluyó que el modelo desarrollado fue apropiado para producir una mejor estimación del inventario nacional de metano producido por el ganado bovino, ya que es lo suficientemente flexible para incorporar nuevos grupos de ganado o esquemas de clasificación, niveles de productividad y una gran variedad de alimentos para el ganado. El modelo también puede utilizarse para evaluar diferentes escenarios de mitigación y servir como herramienta para diseñar políticas de mitigación
Limitations and improvements of the energy balance closure with reference to experimental data measured over a maize field
No full textThe use of energy fluxes data to validate land surface models requires that energy balance closure conservationis satisfied, but usually this condition is not verified when the available energy is bigger than the sumof turbulent vertical fluxes. In this work, a comprehensive evaluation of energy balance closure problems isperformed on a 2012 data set from Livraga obtained by a micrometeorological eddy covariance station locatedin a maize field in the Po Valley. Energy balance closure is calculated by statistical regression of turbulentenergy fluxes and soil heat flux against available energy. Generally, the results indicate a lack of closure witha mean imbalance in the order of 20%. Storage terms are the main reason for the unclosed energy balance butalso the turbulent mixing conditions play a fundamental role in reliable turbulent flux estimations. Recentlyintroduced in literature, the energy balance problem has been studied as a scale problem. A representativesource area for each flux of the energy balance has been analyzed and the closure has been performed infunction of turbulent flux footprint areas. Surface heterogeneity and seasonality effects have been studied to understand the influence of canopy growth on the energy balance closure. High frequency data have beenused to calculate co-spectral and ogive functions, which suggest that an averaging period of 30 min may misstemporal scales that contribute to the turbulent fluxes. Finally, latent and sensible heat random error estimationsare computed to give information about the measurement system and turbulence transport deficienciesEl uso de datos del flujo de energía para validar modelos de superficie requiere que se satisfaga el cierre del balance de energía; sin embargo, esta condición no suele verificarse cuando la energía disponible es mayor que la suma de los flujos turbulentos verticales. Este trabajo presenta una evaluación de los problemasrelacionados con el cierre del balance de energía. Los datos evaluados corresponden a una base de datos de 2012 de Livraga, Italia, obtenidos en una estación micrometeorológica de covarianza eddylocalizada en un campo de maíz del valle del Po. El cierre del balance de energía se calcula mediante la regresión estadística de flujos turbulentos de energía y flujos de calor en el suelo. Por lo general, los resultados indican ausencia de cierre con un desequilibrio medio del orden de 20%. Las condiciones del almacenaje son la razón fundamental de la ausencia de cierre del balance, pero las condiciones de mezcla de flujos turbulentos también desempeñan un papel importante en las estimaciones confiables de estos flujos.Recientemente se ha introducido en la literatura el estudio del balance de energía, como un problema de escala. Aquí se ha analizado un área de origen representativa para cada flujo de energía que interviene enel balance, y el cierre se ha realizado en función de las áreas con huellas de flujos turbulentos. Tambiénse han estudiado los efectos de la heterogeneidad de la superficie y la estacionalidad para comprender la influencia del crecimiento de la cubierta vegetal en el cierre del balance de energía. Se han utilizado datos de alta frecuencia para calcular funciones coespectrales y de ojiva, los cuales sugieren que un periodo mediode 30 min puede perder las escalas temporales que contribuyen a la existencia de flujos turbulentos. Por último, se calculan las estimaciones de errores aleatorios de calor sensible para proporcionar informaciónsobre deficiencias en el sistema de medición y el transporte tur bulento
Seasonal prediction of tropical cyclone activity over the North Indian Ocean using the neural network model
Get PDFA neural network (NN) model is developed to predict the seasonal number of tropical cyclones (TCs) formed over the north Indian Ocean during the post-monsoon season (October, November, December). The frequency of TCs and the large scale climate variables derived from the NCEP/NCAR reanalysis dataset of resolution 2.5º • 2.5o have been analyzed for the period 1971-2013. Data for the years 1971-2002 have been used for the development of the model, which is tested with independent sample data for the years 2003-2013. Applying correlation analysis, five large-scale climate variables, namely geopotential height at 500 hPa, relative humidity at 500 hPa, sea level pressure, and zonal wind at 700 hPa and 200 hPa for the antecedent month September are selected as predictors. Based on some performance parameter statistics, the performance of the NN model is evaluated and the results are compared with the multiple linear regression (MLR) model. From the results it is inferred that the predicted tropical cyclone count by both models is very close to the actual counts for both periods. However, the NN model is found to be superior to the MLR model. This tropical cyclone prediction technique may be useful for operational prediction purposes
Secondary currents: Measurement and analysis
Get PDF Atmósfera 29(1), 23-34 (2016)Fluid dynamics has the purpose of understanding the movement of liquids and gases by functions that describe the distribution of velocities. Some natural phenomena that present these functions are hurricanes, generated by pressure differences; cyclones, developed by the horizontal temperature gradient; and eddies, associated with a hydrostatic pressure gradient. In the particular case of eddies, they generate the so-called secondary velocities, which are flows formed by the presence of unequal forces between a hydrostatic pressure gradient and centrifugal forces, or by shear stresses at the joining of two flows. In addition, this phenomenon is observed in tornados, where the centrifugal force is greater in the upper layer and decreases towards the bottom, whereas the pressure gradient moves from a high to a low pressure; while in rivers it is detected particularly in bends or joins. Understanding the development of secondary currents is important for the reason that flow behavior is a function of the magnitude of these currents; hence their characterization is fundamental. The objective of this study was to obtain the secondaryvelocities developed as an effect of the union of two water currents, based on data acquired from Doppler acoustic recorders. A second objective was to draw the secondary velocities and to show the rotation flow effect, a kind of results that are difficult to obtain in any other way. The flow mechanisms are related with erosion and sedimentation processes; therefore, understanding them might help to evaluate and predict morphological changes in rivers
The influence of large-scale circulations on the extremely inactive tropical cyclone activity in 2010 over the western North Pacific
No full textThis study attempts to understand why the frequency of tropical cyclones (TC) over the western North Pacific (WNP) was a record low during the 2010 season, by analyzing the effect of several large-scale factors. The genesis potential index (GPI) can represent, to some extent, the spatial distribution of formation in 2010. However, the GPI does not explain the extremely low TC frequency. No robust relationship between the TCnumber and El Niño Southern Oscillation (ENSO) was found. A comparison of the extreme inactive TC year 2010 and extreme active year 1994 was performed, based on the box difference index that can measure the quantitative difference of large-scale environmental factors. Dynamic factors were found to be important in differentiating TC formation over the WNP basin between 2010 and 1994. The remarkable difference of monsoon flows in the WNP basin between these two years may be the cause of the difference in TC formation. The unfavorable conditions for TC genesis in 2010 may have also been due to other large scale factors such as: (1) weak activity of the Madden-Julian Oscillation during the peak season; (2) warming of the sea surface temperature in the tropical Indian Ocean during the peak season, causing the development of an anticyclone over the WNP basin and associated with the westward motion of the monsoon trough, and(3) the phase change of the Pacific Decadal Oscillation (more negative) and the two strong La Niña eventsthat have evolved since 2006.Este estudio presenta un análisis de factores de gran escala para entender por qué la frecuencia de formación de ciclones tropicales (CT) en la cuenca del Pacífico noroccidental fue extremadamente baja durante la temporada 2010. Se calculó el índice de génesis potencial (GPI, por sus siglas en inglés) que, en cierto sentido, puede representar la distribución espacial de formación en 2010. Sin embargo, el GPI no puede explicar la frecuencia extremadamente baja observada en dicho año. No se encontró una relación robusta entre el número de CT y el fenómeno El Niño/Oscilación del Sur (ENOS). Se llevó a cabo una comparación entre el año más inactivo (2010) y el año más activo (1994) en dicha cuenca, basada en un índice de diferencia de caja , el cual permite medir cuantitativamente la diferencia entre factores ambientales de gran escala. Se encontró que los factores dinámicos son importantes para diferenciar la formación de CT en la cuenca del Pacífico noroccidental entre 2010 y 1994. La notable diferencia de la circulación monzónica en dicha cuenca entre esos dos años puede ser la causa de la diferencia en ciclogénesis. Las condiciones desfavorables para la ciclogénesis en 2010 pudieron deberse a la influencia de otros factores de gran escala, tales como: 1) la débil actividad asociada a la Oscilación de Madden-Julian durante el pico de la temporada ciclónica; 2) el aumento de la temperatura superficial del mar observado en el Océano Índico, lo cual originó el desarrollo de un anticiclón sobre la cuenca ciclogenética del Pacífico noroccidental y el movimiento hacia el oeste de la vaguada monzónica, y 3) el cambio de fase de la Oscilación Decadal del Pacífico (más negativa) y los dos episodios fuertes de La Niña que se han desarrollado desde 2006