Atmósfera (Journal)
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Preliminary results on the migration of the tropical rainfall zone in a simple climate model
Get PDFTwo numerical experiments were performed with a simple energy balance climate model. One is for a global ocean planet and the other one is for a wet land planet. It was found that the tropical rainbelt maximum migrates, for a land planet, about 30° in latitude, while for the ocean planet, it stays always near the equator. Because of this stationarity of the rainbelt in the ocean planet, a tropical desert is formed besides the extratropical desert, which forms both for land and ocean planet experiments
Changes in the rainfall regime along the extratropical west coast of South America (Chile): 30-43º S
Get PDFThe evolution of annual rainfall along the west coast of South America from 30 to 43º S (central Chile) is analyzed for the period 1900-2007. A prevailing negative trend in annual rainfall has been documented for this region in several previous studies. Here we focus on the significant changes and fluctuations occurring at the decadal time scale, exploring the links with regional atmospheric circulation anomalies associated with large-scale oscillatory modes of the ocean-atmospheric system. In particular, the relatively dry condition that prevailed from the 1950s to the early 1970s in the northern part of central Chile (30-35º S) is consistent with an intensified subtropical anticyclone in the southeast Pacific during a period characterized by a prevailing positive phase of the Southern Oscillation (SO) and the cold phase of the Pacific Decadal Oscillation (PDO). The shift of the PDO toward the warm phase by the mid-1970s was followed by an increased frequency of the negative phase of the SO and associated El Niño episodes. Concurrent weakening of the subtropical anticyclone favored an increased frequency of wet years in this region. Further south the negative trend in annual rainfall that prevailed since the 1950s in the region from 37 to 43º S intensified by the end of the 20th century. Changes in the meridional sea level pressure gradient at mid-latitudes and high-latitudes in the southeast Pacific, which are partially connected to the Antarctic Oscillation (AAO), play a significant role in modulating the interannual rainfall variability in all central Chile, especially during the austral winter semester (April-September). Thus, an intensified (reduced) meridional pressure gradient in that region favors a southward (northward) displacement of the latitudinal band of migratory extratropical low pressure systems and associated fronts. The significant positive trend that both the AAO index and its regional counterpart in the southeast Pacific exhibit since the 1950s may partially explain the observed downward trend in annual precipitation in the southern portion of central Chile, resulting from a reduction in both the frequency of wet days and the intensity of precipitation. Most of the global and regional climate models used to assess future climate scenarios associated with an enhanced planetary greenhouse effect, also call for a reduction of rainfall in this region which is consistent with the positive trend in the AAO predicted by those models
Vulnerability to climate change of marine and coastal fisheries in México
Get PDFThe vulnerability of fisheries to climate change in México is explored on the basis of an overview of the possible impacts of physical variables of ecosystems and habitats which sustain these fisheries, taking in consideration the socioeconomic and ecological problems which hinder their sustainability. Marine environments were analyzed in view of their importance in sustaining the populations of the main commercial species during some stage of their life cycle, and which are susceptible to be affected by climatic variables. We addressed coral reefs, sea grasses, coastal lagoons, wetlands, sea currents, frontal systems and upwelling, based on the climatic scenarios generated by three general circulation models –ECHAM5/MPI, HADGEM1 and GFDL CM 2.0– as well as the scenarios of emissions A1B, A2 and B2 for the years 2030 and 2050. Impact of climate change in ecosystems and its effects on fisheries were examined, specifically with 16 of the main fisheries which constitute more than 70% of the volume and commercial value of national fisheries. The impacts, around which we have to structure adaptation and mitigation strategies, are: increase in sea surface temperature, sea level rise, and the change of precipitation patterns which will affect the volume of river flow.Se estudia la vulnerabilidad al cambio climático de la pesca en México con base en la revisión de los impactos de las variables físicas a los ecosistemas y ambientes que sostienen a las principales pesquerías, considerando los problemas ecológicos y socioeconómicos que actualmente impiden su sustentabilidad. Se analizan ambientes marinos de los que dependen la mayor parte de las especies importantes para la pesca en México en alguna etapa de su ciclo de vida y que son susceptibles de ser afectados por variables climáticas. Los ambientes marinos que se discuten son arrecifes, pastos marinos, lagunas, humedales, corrientes marinas, frentes y surgencias. Con base en los escenarios climáticos generados por tres modelos de circulación general: ECHAM5/MPI, HADGEM1 y GFDL CM 2.0; y los escenarios de emisiones A1B, A2 y B2 para los años 2030 y 2050, se examinan los impactos del cambio climático en los ecosistemas y la afectación que tendría en la pesca, ejemplificando con 16 pesquerías que constituyen más del 70% del volumen y el valor comercial de la pesca nacional. Entre los impactos que afectarían la producción pesquera en México y frente a los cuales hay que dirigir la construcción de estrategias de adaptación y mitigación, destacan el incremento en la temperatura superficial del mar, el aumento en el nivel del mar y la disminución de los caudales de los ríos por cambios en los patrones de precipitación
Radars, an alternative in hydrological modeling. Lumped model
Get PDFThe use of meteorological radars in hydrological modeling is a tool that is becoming more important each day throughout the world. In order to validate its use in hydrological modeling, a study was carried out in the sub-watershed of the Mixcoac river, in the western region of the valley of Mexico, over an area of 31.5 km2. Rainfall data were estimated by the meteorological radar on Catedral hill, 35 km away from the watershed and from the rain gaUges network operated by the Sistema de Aguas de la Ciudad de México (78 rain gauges). The study generated a lumped model of the rainfall-runoff type with input from radar and pluviograph data for calibration. The use of weather radars is shown to be an alternative in the generation of hydrological models. The model was used to prove the goodness of radar data in linear hydrological models of the input-output type
Winter water mass of the Veracruz Reef System
Get PDFFor the first time, the features of the coastal water mass in winter season, spreading over the Veracruz reef system (VRS) have been investigated using hydrographic profiles. The study was performed in two separated surveys of two days of duration in the southern and middle-northern regions of the area. These first measurements showed that there are two most remarkable features: the difference of 5 °C between winter temperature values compared with summer temperature values, and locally (VRS scale) there was a difference between the first and second survey done in the area during the sampling data. It was observed that there was a notable difference in temperature and salinity values of ~ 2 ºC and ~ 2 psu, respectively, between the coastal water mass of the southern (Antón Lizardo Reef System) and those of the middle (Jamapa River) and northern (Northern Veracruz Reef System) regions, due to the passage of a strong (winds blowing between 12.1 to 18 m/s) to fresh (atmospheric temperature minor of 18 ºC) norther. This variability in the water mass composition (with temperature lower than 22 ºC) probably has effects on the development of the coral communities of the sampled area
Seasonal and annual regional drought prediction by using data-mining approach
Get PDFThis study examines the seasonal regional drought analysis based on the standardized precipitation index (SPI) method and the decision tree technique which is a data-mining approach. The cumulative rainfall series for five reference periods (four seasonal and one annual series) were constituted by using monthly rainfalls from 17 stations in Cekerek Watershed, Turkey, which has an area of 1165 440 ha. Regional analysis was performed by forming the stations initially as homogeneous group(s) according to the discordancy criteria considering by l-moment ratios. There was no discordant station according to discordancy measure of site characteristics except for the first reference period. The heterogeneity measures showed that the selected groups were homogeneous. Based on the goodness of fit criteria |ZDIST| the candidate regional distributions having the minimum ZDIST for k-reference periods were the Generalized Pareto (GPA), Generalized Extreme Values (GEV), Generalized Logistic (GLO), Pearson Type III (PE3), GEV and 3-parameter Log Normal (LN3), respectively. The drought categories for each region were predicted by applying the decision tree rules obtained from the training phase of the k-reference periods. The results revealed that there was no significant difference between drought categories calculated from the conventional SPI algorithm and decision tree approaches. Moreover, the accuracy of prediction for k-reference periods was greater than 94%, except for k3 (81.2) and k5 (86.4%) reference periods
Implementation and applications of chaotic oscillatory based neural network for wind prediction problems
Get PDFWind shear, sudden change in the wind direction and speed, is a familiar hazard to aviation as well as a complex and hard-to-predict phenomenon. The causes of wind shear may be different in different locations. In some places it is caused by microbursts, viz. localized columns of sinking air brought by thunderstorms, while in other places wind shear may result from mesoscale weather phenomena. Thus, algorithms and techniques used to predict wind shear caused by microbursts, as in Wolfson et al. (1994), will not be applicable at an airport where wind shear and turbulence arise from larger-scale but local conditions. This paper presents the implementation and applications of chaotic oscillatory-based neural networks (CONN) for predicting sea breeze and wind shear arising from mesoscale weather phenomenon at the Hong Kong International Airport. Using historical local data provided by the Hong Kong Observatory, we show from simulations that CONN is able to forecast the short-term wind evolution and even wind shear events with a reasonable level of accuracy
Emission of methane and nitrous oxide from Vigna mungo and Vigna radiata legumes in India during the dry cropping seasons
Get PDFMethane (CH4) and nitrous oxide (N2O) emission estimates were made for Vigna mungo and Vigna radiata legumes. The affecting soil parameters like redox potential, soil temperature were studied to evaluate CH4 and N2O emissions. The CH4 was negative and N2O was positive for Vigna mungo, almost throughout the cropping period. The redox potential was more than +100 mV during the entire cropping period with a maximum N2O flux of 11.67 μg m–2 h–1. The raise in soil temperature and the redox potential during harvest further increased the N2O flux to 18.38 μg m–2 h–1. The seasonally integrated flux E(SIF) for CH4 and N2O for Vigna mungo was calculated to be –4.06 g.m–2 and 3.38 mg m–2 respectively. Similarly E(SIF) values estimated for Vigna radiata cropping season were 0.009 g m–2 and –7.6 mg m–2, whereas for the post harvesting period the fluxes were 0.02 g m–2 and 4.06 mg m–2 for CH4 and N2O respectively. The soil parameters like organic carbon and nutrients such as ammonia, nitrate and nitrite during the cropping season were evaluated. The emission of greenhouse gases (GHG) was also correlated to various physico-chemical parameters of soil
Climate and climate change in the region of Los Tuxtlas (Veracruz, Mexico): A statistical analysis
Get PDFThis article describes temperature and precipitation patterns of Los Tuxtlas region in southern Veracruz (México). The region is defined here as the volcanic landscape above 100 m elevation (except at the coast), and comprises 315 525 hectares, including a 155 122-hectare biosphere reserve. The area has an elevational gradient from sea level to 1720 m, with two different climates according to Köppen’s climate classification: humid tropical (type A) at low and middle elevations, and moist with mild winters (type C) at high elevations. Our study is based on data from 24 meteorological stations, with varying data records between 1925 and 2006. For each of eleven principal stations, inhomogeneities and unrealistic outliers were corrected with standard methods, and descriptive statistics were calculated. Among these stations, the 30-year average annual mean temperature varies from 24.1 to 27.2 ºC, and the average annual precipitation from 1272 to 4201 mm. Additional measurements indicate locations with over 7000 mm average annual precipitation at higher elevations. Based on this data, and spatial inter and extrapolation modeling with ANUSPLIN, we present three new maps for Los Tuxtlas: for temperature, precipitation, and Holdridge life zones. The time series of temperature and precipitation over 48 years was analyzed with linear regression, employing generalized least squares. There is a highly significant spatial gradient among meteorological stations in both temperature and precipitation, but only a very low and non-significant upward trend in temperature over the years (0.016 ºC per decade). The trend in precipitation is downward, but statistically even less significant (0.23% per decade). Linear regression between annual mean temperature and annual precipitation data predicts such opposite changes between the two variables
Verification of an algorithm (DWSR 2500C) for hail detection
Get PDFThe aim of this paper is to determine the real-time forecast and warning critera for hail events, using height of maximum reflectivity (Hmax), vertically integrated liquid water (VIL), hail occurrence probability (HailP) and reflectivity radar products (PPIZ). In addition, criteria were sought for use in estimating the size of hail stones. The study is based on data supplied by the Bucharest C-band weather radar along with observation data during the 2001-2008 period. The following radar products: HailP, Hmax, (PPIZ) and VIL, have been determined for each hail event reported by the weather station. A number of 320 cases have been analyzed when hail was determined for 20 weather stations in Muntenia area, Romania. One related result is that in situations when the 0 ºC isotherm is between 3000 and 4000 m, the frequency of hail events certified on the ground is 50%. Another conclusion is that if the maximum reflectivity appears at heights between 7000 and 8000 m, there is an approximately 20% chance of hail events. The HailP, Hmax, Reflectivity and VIL were computed both for the exact locations where hail was reported and for an area of 5 km around those locations. The performed analysis showed that both obtained data sets can be used with confidence. A comparison was performed regarding the year 2008 between the values of HailP from the Bucharest vertical sounding and those extracted from the Aladin model, using its requested parameters. The results show an overestimate of the hail occurrence probability (HailP) when the Aladin model was used