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

This paper proposes the use of a cubic polynomial to evaluate the saturation vapor pressure (es) in order to transform the psychrometric equation into a cubic equation in Tw (wet bulb temperature). This is done because it is not possible to write Tw as a direct function of dry bulb temperature (T), relative humidity (RH) and pressure (p). Statistical comparisons show that this polynomial is accurasier than other semi-epirical methods used to calculate es. Results of the third degree equation for Tw were compared whit resultant values of an iterative method and they were satisfactory.

It is believed by investigators that the cause of Quartenary glacial cycles is the variation of astronomical parameters the climatic impacts of which are amplified by changes of atmospheric CO2 concentration.

The feasibility of predicting spring rainfall over Rio Grande do Sul (Brazil) from the prior observations of SO index is examined. It is found that moderate success can be obtained. The optimum data period for deriving the prediction equations is about 11 years.

Manuscript received May 21, 1993; accepted August 26, 1993.

Since 1991, volatile organic compounds (VOC) have been determined in Mexico City metropolitan area (MCMA) using different analyzing methods. samples collected in catridges and canisters are analyzed by gc-ms and hplc. continuos monitoring by a long path differential absorption analyzer (DOAS) has also been performed. The Mexican Petroleum Institute (IMP) along with the USEPA and the collaboration of the Mexican environmental authorities have performed, following the EPA TO-14 method, four sampling campaigns of ambient air in canisters among 1992 and 1993. The campaigns were designed to be performed during March, month in which the worst ozone episodes have taken place. Additional sampling was performed in November in order to compare diferences between seasons.In March 1993, samples in three different kinds of cartridges were used which selectively absorb carbonyl compounds, light hydrocarbons (C2-C4) and heavier hydrocarbons (C5-015).

Direct solar radiation measurements were used to determine the aerosol optical depth (AOD) increase associated with the presence of aerosol and large particles (ash) originating from the 28 March to 4 April 1982 El Chichón eruptions (17.5ºN, 93.3ºW; Mexico) on Mexico City's polluted atmospheric aerosol layer. The results are compared with those obtained at Vancouver, British Columbia, revealing that a first AOD increase occurred in both locations during May, June, and July 1982. However, the Mexico City AOD decay is more extended, not reaching normal climatological values until February 1983. Meanwhile, Vancouver's AOD reached minimum values in September 1982, which subsequently increased over a period from October 1982 to September 1983. This secondary maximum was recorded in Mexico City from March to August 1983. Results suggest that the first AOD increases in May, June and July 1982, both at Vancouver and Mexico City, are due chiefly to short life-time volcanic ash particles being located near the surface. However, the second AOD increases, associated with anomalously colored twilights, corresponds to stratospheric volcanic aerosols.

Cloud water was simultaneously collected in Teziutlan town, located in a mountainous region in the Sierra Madre Oriental, State of Puebla, Mexico, to compare three co-located cloud water collectors. Two of the collectors were passive; the first one was an omnidirectional collector known as ASRC (Atmospheric Science Research Center String Collector). The second was a metallic mesh collector with 0.041-cm diameter stainless steel wires woven on a polyethylene frame. The third one was an active collector in which air is aspirated through a duct at a rate of 3.5 m s-1. Cloud droplets are collected on vertically strung wires on a teflon frame. Liquid water content and collector capacity were evaluated by the corresponding equations. The results indicated that there were not differences in chemical composition concentrations between the passive collectors, however, statistical differences were found between the active and passive collectors. Finally, the collection capacity was higher in the active collector than in passive collectors, due to the inherent differences in design between the active and passive collectors.

Atmospheric lead concentrations associated to particles smaller than 10 µm were measured in Mexico City, to establish changes of levels of this pollutant in three sites (industrial, commercial and residential) for 1990-1991. Moreover, an attempt was made to establish a possible link between this airborne pollutant and blood lead levels reported in children and women living near the sampling sites. A marked gradient in atmospheric lead from North to South is observed with higher and more variable mean lead values in the northern site where industry is located. Lead concentrations and their corresponding variability gradually decrease (from about 1.2 to 0.5 µg m-3) toward the southern suburbs. Moreover, these values are significantly higher during the dry season than in the wet season when a marked washout effect is observed. However, the quarterly averages recorded during the sampling time do not exceed the international standard (1.5 µg m-3). Lead concentrations and corresponding PM10 values showed a significant correlation. This result shows that lead is associated to the fine fraction of airborne particles, with high proportion of them deposited in the respiratory tract. A substantial abatement in levels of atmospheric lead is observed in 1991 with respect to the previous year. This may be explained by the introduction of improved quality gasoline in the capital city. In spite of this measure more than 30 of the evaluated population in 1991 presented blood-lead levels > 10 µg dL-1.

This paper describes temporal cloudiness variability from Nimbus-7 satellite observations and a GCM simulation. The GCM clouds are parameterized using the cumulative normal distribution function to relate fractional cloud amount with large-scale relative humidity. The global distributions of cloudiness characteristics from both data sources are presented, including their temporal means and standard deviations. For the Nimbus-7 observations, the periods are for DJF and JJA, 1979-1985 while the simulated data are for perpetual January and July. Variances contributed by fluctuations with periods between 2.5 to 6 days, and >10 days are extracted. Both observed and simulated cloud variability fields show strong zonal dependence. High-frequency fluctuations are more predominant in the middle latitudes while low-frequency fluctuations predominate in the tropics and the polar regions. In general, unfiltered cloud variabilities are highest in regions associated with cyclolysis. The GCM performs creditably in not only simulating the seasonal means but also the variabilities in the temporal bands examined. Some reasons for the extracted cloud variability patterns at different locations and for different cloud heights are given.

The adjoint method is applied to derive simple integral formulas for the sensitivity study of the Adem Ocean Thermodynamic Model to small variations both in the heat forcing and in the initial and boundary conditions In each formula, the adjoint model solution is a useful source of information about the contribution of such variations to average sea surface temperature anomaly in a certain region. Thanks to special conditions set at inflow and outflow liquid boundaries- the main and adjoint thermodynamic models are well-posed in the sense of Hadamard (1923) not only for closed, but also for open oceanic basins. Balanced and absolutely stable implicit finite-difference schemes of the 2nd order approximation both in space and m time are constructed for the main and adjoint ocean thermodynamic models. The schemes are based on the splitting method and easily solved by the factorization. Both unsplit and split difference operators ofthese schemes satisfy the discreto Lagrange identity at every time step. In the nondissipative and unforced case when there is no flux across the liquid boundaries, the schemes have two conservation laws each.