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

The problem of air pollution in Mexico City is studied through the analysis of a large dataset obtained by an instrumented aircraft during February 1991. These data constitute a unique set in Mexico and provide insight into the vertical structure of the boundary layer and the pollutant species which has not been previously discussed. The results obtained on the evolution and structure of the mixed layer indicate that its height rises from 100 meters during the morning (Sam) to over 2000 meters at 5 pm. Results consistently show that the maximum in ozone concentration is not observed at the surface, but at about 700 m on average above it near midday. This peak, with an average concentration over the observational period of 167 ppb, appears to be a transient feature, with concentrations becoming more uniform with height in the afternoon. The vertical profiles of nitrogen oxides and sulphur dioxide indicate that concentrations are highest during the morning and steadily decrease with height, suggesting that sources for these species are located near the surface, as was expected. There appears to be no correlation between the amount of nitrogen oxides observed during the take-offs and the ozone concentrations observed during landign (2-3 hours later). When the variables are normalized by the mixed layer height the results indicate that the ozone observed is fairly independent of the nitrogen oxide concentrations observed earlier. A reduced range of values of the ratio of ozone accumulated in the mixed layer and the layer height is consistently day found during the observational period. Aerosol particles near the surface show maximum concentration during the morning hours, but in contrast, during the course of the day, there is a marked increase in their concentrations at higher levels in the boundary layer suggesting that possibly gas to particle conversion is responsible for the observed increase.

The aridity conditions in the northwest Mexican region formed by the states located around the Gulf of California are studied. The Annual Arid Cover Index (AACI) is defined as the fraction of the studied are with Martonne aridity index values less or equal to 5. The AACI is used to describe variations in the extension and localization of the extremely arid zones during the 1950-1990 period. The results show a tendency of the extension of the arid zone to reduce: 30% in 41 years.  A statistically significant explained variance of 32% between the AACI and the sea surface temperature (SST) of the California Current zone was obtained. correlation between the southern oscillation and the pacific north america indexes show as smaller variance: 17 and 3 % respectively. The multiple regression model gives a total coefficient of determination of 42 %. The variations in the geographical localization of the extrmely arid zones show aht the Altar Desert and the meridional zone of the Baja California Peninsula have the more persistent arid conditions in the studied region.

The evolution of a ridge-trough system that occurred in the periphery of the Antarctic in late July 1986 is examined. A cyclonic disturbance within the polarward side of a blocking anticyclone, developed into an intense closed circulation to the east of the Drake Passage. The maturity and decay of the system took place over the Weddell Sea, a location for cyclolysis according to the climatology. The eddy kinetic energy budget of this wave was evaluated, using 12-h ECMWF operational analyses, in order to identify the physical processes that contributed to its development. Particularly, attention was given to the role of the downstream baroclinic development process in the growth and decay of energy centers associated with the cyclonic wave. The initial growth of an eddy kinetic energy center near 90ºW was mastered by the convergence ofageostrophic geopotential fluxes, originated from a previous energy center in dissipation stage. The center developed in a region of relatively low baroclinicity and then the incidence of the baroclinic conversion process was not significant. As the center intensified, it produced strong radiation of energy downstream to the east of Drake Passage, where a deep cyclone developed, with a new associated eddy kinetic energy center. It was found that the convergence of ageostrophic geopotential fluxes and, in lesser extent, the baroclinic conversion were the most important physical processes during the early stage of growing. Finally, this last energy center decayed, mainly, by flux divergence.

Using a network of 16 urban/suburban and rural pan evaporation (pe) stations in Mexico City and its environs, an attempt is made to assess the comparative evaporative characteristics of different areas in a large city located in an elevated inland valley in the tropics. Significant parallel increases in pan evaporation and heat island intensity have been observed in the central and western portions of Mexico City for the period 1967-88. It is suggested that pan evaporation increase is linked to the observed increase in the intensity of the heat island related to the accelerated urbanization of the capital City. m contrast over the eastern suburbs the establishment of a large (9500 Ha) adjacent revegetation project has apparently influenced pan evaporation to decline in spite of the increasing presence of the heat island. Association of pan evaporation to other climatic elements such as insolation, precipitation and wind velocity is also explored.

In this article a physical modelization of the atmospheric pollution was considered. The objective was to determine the concentrations of pollutants in a receptor station reproducing the way followed by the air mass and simulating the physical and chemical processes involved during this way. To do that we used a Lagrangian model. To estimate the quality of the model a comparision betweeen the theoretical concentration from the model and the observed concentrations is done. the model uses the air mass trajectories arriving at the receptor station calculated from the Limited Area Model (LAM). These trajectories let us know the air mass position each 6 hours. once the initial moedl had been run, several parameters were modified with the aim of reproducing letter the conditions of The Iberian Peninsula. The considered pollutans wer the SO2 and SO42-and the chosen station was Logroño (Spain).

Both statistical methods and mathematical modelling are used to study the distribution and evolution of various climatic characteristics in the humidity field of Mexico. The statistical analysis provides local humidity estimates based on Kriging's method and Shepard's interpolation. A mathematical limited area model of humidity transport (taking account of topography) is formulated for a region of Mexico in the a-system of coordinates. The model is balanced and well-posed according to Hadamard, that is, both of its solutions are unique and stable to perturbations in the initial and boundary conditions, m the absence of the humidity sources and sinks the model has two conservation laws

This paper examines aspects of the atmospheric boundary layer (ABL) for several U. S. coastal and inland locations around the Gulf of Mexico. Simulations are performed using the Oregon State University (OSU) planetary boundary layer model under a Gulf of Mexico return-flow event. For the model analyses, the ABL heights are obtained using soil moisture values from the Eta model. The ABL heights obtained from these 24-hr forecasts are then compared with other standard formulations. It is shown poor forecasts of the ABL height in the model under very stable conditions can be prevented by using an interpolation formula. Results confirm that friction velocity in the boundary layer along the Gulf coast is small. A strong relationship between friction velocity and Monin-Obukhov length at coastal locations is likely due to surface fluxes with relatively unimportant heat flux. At coastal locations of Florida and Texas, mechanical turbulence causes large temperature structure parameter at the surface since wind speed is usually calm in the model forecasts.

This paper is concerned with the sensitivity of the forecasts obtained from the "Florida State University Atmospheric Boundary Layer (FSU1DPBL) Model" when solely considering a variation in the roughness length parameter. The model is mainly used to evaluate the sensitivity of the roughness length of momentum on the model forecasts. The roughness length calculations are perfomed using both wind speed components and wind direction. Based on these calculations, the commonly used values of roughness length of momentum indicated in the literature is compared to that for Tallahassee (TLH) calculated from observations. In addition, model forecasts obtained using the calculated roughness length are compared with those using the classical value of the roughness length. The focus on these comparisons is mainly on the variations, if any, in the forecasts for the atmospheric boundary layer (ABL) height, sensible heat flux, soil heat flux, latent heat flux, and 10-meter wind speed. Results show that the fluxes do not have much variation when using both classical roughness length and the calculated roughness length. However, the 10-meter wind speed appears to be overestimated using the classical roughness length value in comparison to the calculated value.

The area-averaged stratiform precipitation rate can be estimated by equating the downward flux of precipitation with the upward flux of vapour. This study evaluates the usefulness of this approach by comparing the estimated rainfall rate with that computed using a time-dependent non-hydrostatic cloud model. Comparison with the cloud model results reveals how sensitive the water flux balance rainfall rates are to the magnitude and depth of the low-level convergence. It is found that the numerical cloud model overestimated rainfall observations for a case study of central Alberta for which the initial and boundary conditions of the convergence field were adopted from Doppler radar observations. The water flux balance equation and the cloud simulations agreed in that the rainfall rate became stronger when either the magnitude of the surface convergence or the convergence depth was increased. However, the water flux balance equation consistently underestimated the model rainfall rates. Also, rainfall estimates from water flux balance equation were not sensitive to the divergence aloft, whereas the model rainfall was dependent on the distribution of upper-level divergence. The basic conclusion to be drawn is that the water flux balance equation is easy to use, but can provide only a crude estimate of rainfall with a bias to underestimate.

The vertical profiles of the boundary-layer aerosols obtained with a bistatic Argon ion lidar system at the Indian Institute of Tropical Meteorology (IITM), Pune, India, during two contrasting, successive south-west (summer) monsoon seasons of 1987 (weak monsoon year) and 1988 (active monsoon year) have been examined. The concurrent meteorological parameters such as temperature, relative humidity and rainfall over Pune have also been studied. It is noticed that the aerosol columnar content (integration of vertical profile throughout the height range) is greater during the active monsoon months and less during the weak monsoon months. Thus the monsoon season total rainfall during 1987 and 1988, apart from other meteorological parameters, shows close correspondence with the aerosol columnar content over the experimental station. A brief description of the lidar experimental setup and the database is given. The observed association between the aerosol columnar content and the monsoon activity is explained in terms of the environmental and meteorological conditions prevailing over Pune.