Atmósfera (Journal)
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Turbulence integral length and footprint dimension with reference to experimental data measured over maize cultivation in Po Valley, Italy
Get PDFThe atmospheric turbulence in the planetary boundary layer (PBL) governs the mass and energy exchange over the soil-vegetation-atmosphere system. Micrometeorological stations based on the eddy-covariance technique have been recently developed for the assessment of latent and sensible heat fluxes through high frequency measurements of the fluctuating component of wind velocity, temperature and air water content in the PBL. Correct interpretation of such measurements requires assessment of the actual source area (footprint) contributing to the eddy fluxes (latent and sensible heat). Many different approaches have been developed to estimate the source area function but there is no general consensus on the accuracy and applicability of these methods. The objective of this work is to demonstrate the existence of a relationship between the representative source area for eddy covariance measurements, and the large eddies responsible for the transport of turbulent kinetic energy (TKE). Moreover, the energy balance closure was used to analyze the possible effects of the different lengths of the source area on the heat fluxes. A series of measurements were carried out in a micrometeorological eddy covariance station located in a maize field in Landriano in Po Valley (PV), Italy. The results show that the dimension of the large eddies is tightly bound to the footprint size, leading to a new approach to study the eddy covariance measure based on the assessment of the turbulence scale.La turbulencia atmosférica en la capa límite planetaria (PBL, por sus siglas en inglés) gobierna el intercambio de masa y energía en el sistema suelo-vegetación-atmósfera. Actualmente existen estaciones micrometeorológicas basadas en la técnica de covarianza turbulenta para la evaluación de los flujos de calor latente y sensible a través de la medición de las fluctuaciones de la componente vertical de la velocidad del viento, de la temperatura y del vapor de agua en la PBL. La interpretación correcta de estas mediciones requiere de la correcta evaluación del área de origen donde se generan los flujos turbulentos. Se han desarrollado muchos enfoques diferentes para calcular esta área de origen, pero no existe ningún consenso general sobre la precisión y la aplicabilidad de esos métodos. El objetivo de este trabajo es demostrar que existe una relación entre el área de origen típica que afecta al instrumental y los torbellinos que son responsables del transporte de la energía cinética turbulenta (TKE, por sus siglas en inglés). Se realizó una serie de mediciones con una estación micrometeorológica situada en un campo de maíz en Landriano, en el valle del Po, Italia. Los resultados demuestran que la dimensión de los torbellinos está en estrecha relación con la dimensión del área de origen, proponiendo un nuevo enfoque para el estudio de la covarianza turbulenta con base en en las dimensiones de los torbellinos
Interannual deviations of long-term data from observations and contrasting with reanalysis data from the oceanic station at Islas Marías, Nayarit, Mexico
Get PDFWe prepared a synthesis of historical weather conditions for Isla María Madre (1922-1989) to reflect conditions that impact the mainland of México. Observations were compared with regional reanalysis (RR) data in the same area. The results indicate that air temperature, atmospheric pressure, relative humidity, and precipitation in both sources of data display the annual signal. Observations and RR data show differences in climate analysis, mainly in the phase of air temperature and relative humidity. These differences can be explained by the smoothness and the methods used to estimate the RR data.Se realiza un análisis climatológico de los datos meteorológicos históricos de Isla María Madre (de 1922 a 1989) para evidenciar las condiciones que tienen impacto en el territorio continental de México, y se comparan con datos de reanálisis regional (RR) en la misma zona. Los resultados indican que la temperatura del aire, presión atmosférica, humedad relativa y precipitación, en ambos tipos de datos, responden a la señal anual. Los datos de RR e in situ muestran diferencias en cuanto a comportamiento climático, principalmente en las fases de temperatura del aire y humedad relativa. Estas diferencias pueden deberse a la forma en que se obtienen y suavizan los datos de RR
Assessing current and potential patterns of 16 forest species driven by climate change scenarios in México
Get PDFIn order to analyze the impacts of climate change on species endowed with forestry relevance, the present study practiced simulations in the potential distribution of 16 forest species inside the Mexican Republic’s temperate, tropical, and semiarid zones. For the examination of this effect we pictured the base scenario, as well as three models of climate change (GFDL-CM-2.0, MPI-ECHAM-5, HADGEM-1) that would take place under the socio-economic scenarios A2 and B2 by 2050. The methodology consists in: 1) a modeling of climatology corresponding to the period 1950-2000 (base scenario); 2) a consideration of the reasons for the change in precipitation and temperature within each one of the three climate change models; 3) a calculation of the soil humidity balance; 4) the creation of matrices of the forest species’ environmental requirements, and 5) a proposal for a potential spatial distribution of the species. The results show that, because of a rise in temperature and a decrease in precipitation along the entire national territory almost every month, each one of the forest species living in the temperate zones will be affected within the span of time considered. Among the species of the tropical zones, there appears a substantial decrease in the levels of those with the highest suitability, which is linked to the restrictions that are set on their development as the dry period is heightened. As for the species of the arid and semi-arid regions, the models indicate that an increase will be marked on the area of those with no suitability, which is associated with the enhancement of hydric deficit. Of the climate change models here considered, the HADGEM-1 establishes the most restrictive conditions, the MPI-ECHAM-5 establishes an intermediate situation of affectation, and the model GFDL-CM-2.0 establishes the least affectation. Geographically, the country does not present constant changes in the potential distribution of the species; these latter vary according to the climate change model that has been used, the species that has been analyzed, and the ecological zone that has been delimited.Se analizaron los impactos del cambio climático en el sector forestal mediante simulaciones en la distribución potencial de 16 especies forestales en la República Mexicana, para zonas templadas, tropicales y semiáridas. Se estudiaron para el escenario base así como para tres modelos de cambio climático (GFDL-CM-2.0, MPI-ECHAM-5, HADGEM-1) bajo los escenarios de emisiones socioeconómicos A2 y B2 al horizonte de tiempo 2050. La metodología consistió en: 1) modelación de la climatología en el periodo 1950-2000 (escenario base), 2) aplicación de razones de cambio de los tres modelos de cambio climático, 3) cálculo del balance de humedad en el suelo, 4) creación de matrices de requerimientos ambientales de las especies forestales y 5) simulación de la distribución potencial espacial de las especies. Los resultados obtenidos muestran que todas las especies forestales de las zonas templadas se verán afectadas para el horizonte de tiempo considerado, como consecuencia del incremento en la temperatura en todo el territorio nacional y la disminución de la precipitación en casi todos los meses del año. En las especies de zona tropical, con excepción de Cedrela odorata, se presenta una disminución considerable en los niveles de mayor aptitud, lo que se asocia a restricciones para su desarrollo al incrementarse el periodo seco, asimismo, las áreas templadas, que tendrán un aumento en la temperatura, serán de aptitud limitada para estas especies. Para las especies de la región semiárida y árida, los modelos reportan que se espera un incremento de la superficie sin aptitud, lo que se asocia al incremento del déficit hídrico y en las zonas que actualmente se consideran marginales las restricciones serán más severas. De los modelos de cambio climático considerados, el HADGEM-1 establece las condiciones más restrictivas, el MPI-ECHAM-5 establece una situación intermedia de afectación negativa y el modelo GFDL-CM-2.0 establece incrementos de la superficie con cierto grado de aptitud. Geográficamente, el país no presenta cambios constantes en la distribución potencial de las especies, estas varían de acuerdo al modelo de cambio climático utilizado, la especie analizada y la zona ecológica delimitada
Comparison between LDA technique and fuzzy membership roster method for pre-monsoon weather forecasting
Get PDFIn the present study, an attempt is made to propose a new operational technique for weather forecasting at Kolkata (22.53º N, 88.33º E), India, during the pre-monsoon season (March, April and May). The technique is based on fuzzy membership roster method. It can handle inherent non-linearity in a physical phenomenon. To establish the new method, a comparative study is performed between the existing multivariate technique, the linear discriminant analysis and the newly suggested technique based on fuzzy membership roster method. It is interesting to note that for the prediction of weather of next 12 hours based on Radio/Rawin Sonde observation at 1200 UTC of a day, the fuzzy membership roster method is better than the multivariate technique. Both the methods are however almost equally suitable to predict the weather of the next 12 hours based on Radio/ Rawin Sonde observation at 0000 UTC. So, the fuzzy logic based technique, adopted here, is as efficient as the linear statistical rules, but computationally simpler. The degrees of compatibility and the discriminant functions are defined using a training data set for the period 1985-1996 and validated for the period 1997-1999
Evaluation of long-term NDVI time series derived from Landsat data through blending with MODIS data
Get PDFThe aim of this study is to capitalize on the spatial detail of Landsat and the temporal regularity of MODIS acquisitions using a fusion approach (Spatial and Temporal Adaptive Reflectance Fusion Model, STARFM). Specifically, the 30 m Landsat-7 ETM+ (Enhanced Thematic Mapper plus) surface reflectance was predicted for a period of eight years (2002-2009) as the product of observed ETM+ and MODIS surface reflectance (MOD09Q1) on the predicted and observed ETM+ dates. A pixel based analysis for observed ETM+ dates covering winter and summer crop seasons showed that the prediction method was more accurate for NIR (mean r2 = 0.87, p ≤ 0.01) compared to red band (mean r2 = 0.65; p ≤ 0.01). The NDVI was computed from observed Landsat and predicted surface reflectance. The difference between NDVI from predicted and observed ETM+ data (prediction residual) was compared with the temporal residuals of NDVI from observed Landsat and MODIS data at two different dates. The prediction residuals for NDVI (spatial mean value of 0.0085) were found to be significantly lower than the temporal residuals (spatial mean value of 0.056 for MODIS and 0.051 for observed ETM+) implying that the prediction method was better than temporal pixel substitution. Investigating the trend in synthetic ETM+ NDVI values over a growing season revealed that phenological patterns were well captured. A direct comparison between the NDVI values obtained from MODIS and synthetic ETM+ images has shown a good consistency of the temporal dynamics but a systematic error that can be read as bias (MODIS NDVI over estimation). The relationship between synthetic ETM+ NDVI with observed precipitation and evaporation data was also studied and it was observed that monthly total precipitation and monthly evaporation of the preceding month have higher correlation coefficients (r2 = 0.56 and r2 = 0.59) with mean monthly synthetic ETM+ NDVI
Analysis of the effects of climate change on plant communities and mammals in México
Get PDFThe current study proposes two methodological approaches for analyzing the effects of climate change on biodiversity, one at the level of bioclimatic zone, and the other one at the species level. Three general circulation models were applied to nine bioclimatic zones and 61 species of mammals in México for the 2050 time horizon: ECHAM5/MPI, UKHADGEM1 and GFDL CM 2.0, each one with two emissions scenarios, A2 and B2. In the case of bioclimatic zones a multinomial logit model was used based on data from surveys of vegetation, climate data and soil information in order to obtain probabilities of occurrence. In the case of mammals, ecological niche models were made for each of them as well as models of their distribution in the country within each bioclimatic zone. The results show that ECHAM and Hadley coincide with tendencies towards drier conditions mainly in northern México, in contrast with GDFL with less severe results. Differences are noticed according to the applied emission scenarios. Results at a specific level coincide roughly with their corresponding bioclimatic zones. By 2050 it is generally expected that almost half of all analyzed species will lose around 50% of their area of distribution as a result of the impact of climate change
Observed solar dimming in the Wider Caribbean
Get PDFWe present the results of a study of the dimming-brightening phenomena in the Wider Caribbean. The dataset consisted of time series of global radiation from 30 surface stations covering the period 1961-1990. The stations were distributed over the entire region: three in Florida, USA, five in the Caribbean, three in México 17 Venezuela and one in Honduras. Results showed in general a predominance of the dimming over this period, registered at 20 of the stations, while brightening was only noted at the remaining 10 sites. Associated trends were statistically significant, at 5% level, at 21 of the total 30 stations (70%). In particular 16 of the stations registering dimming and 5 of the ones showing brightening had statistically significant trends. Considering the physico-geographical distribution of the stations they were grouped in continental and insular-peninsular. The significant trends averaged –0.72 Wm–2 per year for continental stations and –0.82 Wm–2 per year for the insular-peninsular ones. Dimming was more frequent in continental areas, but more intense in the insular peninsular ones
Statistical prediction of monthly mean temperature anomalies in the United States during winter months
Get PDFAnomalies of mean monthly air temperature at 50 surface stations in the contiguous United States during the winter months of January, February and March from 1951 to 1980 are statistically screened as functions of earlier, centered or future time means of different length. Potential predictions include fields of 700 mb height, air and sea surface temperature, snow cover and ENSO indices. Future height anomalies are damped in accordance with the accuracy of daily numerical prognoses out to 10 days produced operationally at the National Meteorological Center. All statistical significance is evaluated by means of Monte Carlo simulations. The principal result is that judicious use of 1-10 day numerical height predictions offers the greatest promise for immediate improvement of monthly mean temperature forecasts
Decision trees to determine the possible drought periods in Ankara
Get PDFGlobal climate change causes a decrease of precipitation in Turkey, as in many other parts of the world. As a result, droughts have now occurred over a larger area and in a more drastic way than in the past. Determining the factors in the formation and early prediction of drought will allow required measures of prevention to be taken in time. The present study evaluates drought conditions on monthly and yearly bases, with the measurements of precipitation, wind, humidity and temperature taken in the Ankara region between 1926 and 2006 using the techniques of decision trees. The obtained results demonstrated that the province of Ankara has a generally normal and near-normal arid climate and that the precipitation amounts in all months and precipitation and wind in January, should be taken into consideration to determine such aridity
Average conditions of thermal stress in Mexican cities with more than one million inhabitants in the face of climatic change
Get PDFHuman bioclimatic scenarios are presented for Mexican cities with more than a million inhabitants. For this, both urban and global warming were considered, the former having been inferred from demographic data, and the latter from the output of general circulation models. Thus, it was possible to estimate increases in temperature and modifications in hygrometric conditions, which were then used to estimate the human bioclimate for the period of 1981-2000 and the decades of 2030 and 2050, as well as the domestic electrical consumption for air-conditioning in housing resulting there from.Se presentan escenarios de bioclima humano para ciudades mexicanas de más de un millón de habitantes, considerando el calentamiento urbano y el calentamiento global. El primero se infirió a partir de datos demográficos, y el segundo, de las salidas de los modelos de circulación general. Así, fue posible estimar incrementos en temperatura y modificaciones de las condiciones de humedad que se tradujeron en estimaciones del bioclima humano para el periodo 1981-2000 y las décadas de 2030 y 2050, y sus consecuentes consumos eléctricos domésticos por climatización de viviendas