Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The problem of propagation of pollutants emitted into the atmosphere by various industrial sources is formulated using the two-dimensional transport equation. An adjoint transport model and dual principle are derived that permit to impose sufficient restrictions on the emission rates of each industrial pollution source in order to maintain average pollution concentration in an ecologically important zone below a maximally admissible value. Two strategies of control of the emission rates are suggested. The first one is based on the minimization of the L2-norm of the emission rates subjected to a linking equation determined by the dual principle. The second strategy is derived from an adequate limitation on the temporal behavior of the emission rates. Both the strategies are defined in terms of the adjoint transpot problem solution.

Nowcasting of daily rainfall using physical initialization provides a dynamical and thermodynamical structure consistent with respect to the imposed 'observed' rainfall. This procedure provides a very high skill for the modeled ram as compared to the observed rainfall totals. This same procedure is extended over periods of months to illustrate the very high skill for recovering the 'observed rain' from the model by using physical initialization within a month long data assimilation. This procedure also provides details of the temperature, wind, humidity and surface pressure field that are consistent with the month mean rainfall field. Such data sets are useful for the validation of global climate models. In this note, we present the impact of physical initialization on rainfall climatology. We compare the Florida State University (FSU) rainfall climatology with the European Centre for Medium Range Weather Forecast (ECMWF) and the National Center for Environmental Prediction (NCEP) reanalysis.

The zonal state of the atmosphere is reconsidered using interaction coefficients to simulate the interplay between the atmospheric waves and the zonally averaged state. In order to correct too large easterly wind in an earlier model the interaction coefficients are specified as functions of latitude. The revised procedure is applied to a shallow water model in which addition of fluid is an analogue to the heating of the atmosphere. With a symmetric forcing the geopotential and the zonally averaged horizontal velocity should also be symmetric fields, while the stream function and the vorticity should be anti-symmetric. In the earlier calculations the zonally averaged winds were of too strong in the region close to the equator although the direction was determined in a correct way. The present calculations give an improved result with respect to the tropical easterlies. In the integrations it has been assumed that the meridional transport of vorticity may be described by interaction coefficients. This assumption makes it possible to determine in an indirect way the meridional momentum transport.

The thinning of the stratosphere ozone layer in the Antarctic region is studied by considering ground-based observations at Belgrano Station (78.0ºS; 38.8ºW). Gumbel's first distribution of extreme values is used to evaluate the highest depletion of the Southern ozone hole for the spring months of 1998. According to the present study we predict that the expected largest yearly deviation of the ozone layer density during 1998 would be (109 ± 15)DU. This result agrees remarkably well with the measured value of 102 DU as obtained on October? of 1998 at Belgrano Station.

The warm an cold events in the Tropical North Atlantic (6-22°n,15-80°w) region are quantified using sea using sea surface temperature (sst) normalizad indices. a arm (cold) event was definied if the 5-mounth running mean index was above (below) the fourth (second) quintile for six or more months. The event occurrence was non-periodic and the durations showed great variability. Aarm and cold events tend to begin during the first semester of the year and end during the secondo semester.

On the basis of principal component analysis of long-term climatological records, regression models are formulated and forecast experiments are conducted for monthly temperature and precipitation of the Ozark Highlands area, a large area of low mountains and plateau in the south central midwestern United States. Predictors include global sea surface temperatures, hemispheric upper air fields and the local climate observations. The experiments for all months of the year are performed with the data from continuous 15-year segments of 1961-75 to 1980-94 for those years beyond the respective data segments. Relationships between regional-scale and large-scale climate variables are investigated by cross-correlation analysis to identify useful teleconnections for seasonal-range forecasting. The predictability of the Ozark Highlands climate is examined with the multiple linear regression scheme and the principal component regression scheme. It is shown that the forecast performance by the latter is superior to that of the former. The results of the extensive forecast experiments reveal the useful and stable predictability of the Ozark Highlands climate elements. The validity of the forecasting models is verified for up to 10 years after the data period of regression formulation.

Outdoor smog chambers experiments were performed on air to determine the answer of maximum ozone levels to changes in the initial hydrocarbons, HC, and nitrogen oxide NOx. These captive-air experiments under natural irradiation were carried out. Typically, eight chambers were filled with Mexico City air in the morning. In some of those chambers, the initial HC and/or NOx concentrations were varied by 25%to +50% by adding various combinations of a mixture of HC, clean air, or NOx (perturbed chambers). The Os and NOx concentration in each chamber was monitored throughout the day to determine O3 (max). The initial HC and NOx concentration effects were determined by comparing the maximum ozone concentrations measured in the perturbed and unperturbed chambers. Ozone isopleths were constructed from the empirical model obtained of measurements of the eight chambers and plotted in a graph whose axes were the initial HC and NOx values. For the average initial conditions that were measured in Mexico City, It was found that the most efficient strategy to reduce the maximum concentration of O3 is the one that reduces NOx.

A comparative study has been made in order to address some scientific issues like changes in precipitation and temperature patterns for the premonsoon season during the period 1973-92 over Gangetic West Bengal and its neighbourhood, a region in the eastern part of India. Though premonsoon precipitation contributes only about 12% of the annual rainfall, it is the maximum amount outside the monsoon season. It also occurs after a wide gap of eight months. While constructing the data series, a particular area has been identified where maximum reduction in precipitation occurs in the recent period 1983-92. Statistical analyses with the data series reveal that decrease in precipitation and increase in mean temperature in the month of March are statistically significant. April and May follow the same trend though they are not statistically significant. Integrated Differences Curve shows invariably a reverse associateship between the mean temperature and precipitation.

This work is aimed at studying the interannual variability of surface temperature cold spells and warm spells due to cold-and warm-air incursions. The effect of the ENSO event on the occurrence of extreme spells having three different indices was studied In order to track changes during the 1959/96 period, spell parameters, persistence and intensity, have been studied from daily temperatures. The number of extreme spells per year show low frequency variability plus a biennial variability, which is more important in its intensity than in its persistence, and in summer rather than in winter. The number of extreme warm spells increases until the end of the sixties and seventies, reflecting an increase of northeasterly flow. From then onwards, the trend starts to decline significantly over northern Argentina. The interannual variability of extreme winter cold spells increases from the 80's onwards, indicating the variation of anticyclone permanence over the country. Cases are more numerous in the latest years. Extreme spell occurrence in northern Argentina is closely linked to the El Nino phenomenon. Winter warm spells are more persistent in an El Niño (0) year and more intense and persistent in the year following El Niño. In summer, however, these is either no difference or the relationship is reversed, resulting in more intense situations in November and December in the case of La Nina. Cold spells reaching the northeastern most part of the country are more persistent when La Niña occurs, the conclusion being that the region would be affected by extreme cold spells when La Niña is active.

In this research, volatile organic compound emissions were characterized from gasoline and diesel vehicles. Sampling campaigns in the Metropolitan Area of Mexico City were designed and carried out in tunnels, crossroads, and truck and bus terminals. The samples were analyzed with gas chromatography getting more than 250 different compounds, being more or less 60 of them the 80% of all the emissions. The most abundant are the two carbon compounds, as a result of the combustion, and compounds related to fuels composition, like isopentane, xylenes, toluene among others. The profiles obtained in tunnels and crossroads were very similar with the exception of the 3 and 4 carbon compounds, which were found in bigger proportion in the profiles at crossroads. This may probably be due to the blend with the ambient air. The profiles corresponding to trucks and buses have a smaller content of two carbon compounds and a bigger content of xylenes, toluene and ethylbenzene. The variations in the proportion of the compounds allow to differentiate the profiles of vehicles using gasoline and diesel.