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

We developed a procedure to forecast, with 2 or 3 hours, the daily maximum of surface ozone concentrations. It involves the adjustment of Autoregressive Integrated and Moving Average (ARIMA) models to daily ozone maximum concentrations at 10 monitoring atmospheric stations in Mexico City during one-year period. A one-day forecast is made and it is adjusted with the meteorological and solar radiation information acquired during the first 3 hours before the occurrence of the maximum value. The relative importance for forecasting of the history of the process and of the meteorological conditions is evaluated. Finally an estimate of the daily probability of exceeding a given ozone level is made.

A generalized frontogenesis function is defined in terms of the ice-liquid water potential temperature, which is a thermodynamic variable conservative under all water phase changes. The generalized frontogenesis function is the projection of a new vector, Q*, on the quasihorizontal ice-liquid water potential temperature gradient. Q* can be seen as the diabatic version of the quasigeostrophic Q-vector. In regions of large latent heat release due to phase change, the generalized frontogenesis function, F*, is a more complete and precise tool for delimiting upward air flow in frontal zones than the classical quasigeostrophic frontogenesis function. The proposed quasigeostrophic frontogenesis function is tested on a real meteorological situation characterized by the genesis and development of a warm front over northern Iberian Peninsula. The new quasigeostrophic frontogenesis function is compared with the classical Pettersen's function obtaining an improvement not only in the diagnosis of frontal development but also in the location of frontal zones.

AA* indices of values greater than 60 10-9 Tesla are considered in order to characterize geomagnetic storms since the available series of these indices comprise the years from 1868 to 1998 (the longest existing interval of geomagnetic activity). By applying the precursor technique we have performed an analysis of the storm periods and the solar activity, obtaining a good correlation between the number of storms (α) (characterized by the AA* indices) and the amplitudes of each solar cycle (ζ) and those of the next (µ). Using the multiple regression ^method applied to α = A + Bζ + Cµ, the constants are calculated and the values found are: A = -33 ± 18, B = 0.74 ± 0 13 and C = 0.56 ± 0.13. The present statistical method indicates that the current solar cycle (number 23) would have an upper limit of 202 ± 57 monthly mean sunspots. This value indicates that the solar activity would be high causing important effects on the Earth´s environments.

Applying the concept of effective temperature (ET), a scenario of human bioclimatic conditions for Mexico City is presented by using results from both GCM regional predictions for C02 doubling and temperature trend projection from an urban station. Current and future bioclimatic maps for Mexico City and its conurbation are presented. Current environmental conditions will likely change toward a warmer atmosphere due to both the urbanization process and global greenhouse effect. The impact on the population will be more important during the warm season (March-May) when the bioclimate of the city will likely shift away from current neutrality to the next comfort scale category (ET 24-27ºC) of warm conditions covering most of the capital city.

Optical and thermal properties of soils are important input data for the meteorological and photochemical modules of air quality models. As development of these models increase on spatial resolution good albedo data become more important. In this paper measurements of surface albedo of UV (295-385 nm) and visible (450-550 nm) radiation are reported for different urban and rural surfaces in the vicinity of Mexico City. It was found for the downtown zone an average albedo value of 0.05 which is in very good agreement with reported values for urban surfaces. Our albedo values measured in UV region for grey cement and green grass are of 0.10 and 0.009, respectively, and quite similar to those found at the literature of 0.11 and 0.008 for those type of surfaces.

Documental sources and categorization techniques were used to construct a series of the annual hail intensity in Mendoza area (Argentina). When the temporal series by means of Singular Spectrum Analysis (SSA) and the Maximum Entropy Method (MEM) was analyzed, we found interdecadal oscillations of periods of about 20 years and interannual oscillations of about 4 and 9 years. In addition when detrented-data were used a low frequency oscillation of about 72 years also appears.

A numerical algorithm for the normal mode instability study of a steady nondivergent flow on a rotating sphere is developed. The algorithm accuracy is tested with zonal solutions of the nonlinear barotropic vorticity equation (Legendre polynomials, zonal Rossby-Harwitz waves and monopole modons).

The impact of gravity wave drag (GWD) on the COLA (Center for Ocean-Land-Atmosphere Interactions) –GCM is studied by simulating two pairs of 30-day extended range forecasts. One is initialized on January 8, 1990, and the other on July 15, 1989. With each initial condition forecasts were made both with and without the GWD effects. The results show that GWD effects improve the forecast for both January and July particularly in the winter hemisphere. The GWD reduces the westerly bias in the zonal wind and the cold bias in the temperature. As a consequence of the changes in the momentum and temperature there are changes in the meridional mass transport such that monthly mean sea level pressures are improved particularly in the polar regions. Furthermore, as the westerly bias in the zonal momentum is reduced the momentum of the large scale flow is brought down to the Earth's surface where it is dissipated. This dissipation process increases the effective surface drag and enhances the mean meridional circulations. The results indicate that the mean meridional circulations are enhanced by 15 and the divergent kinetic energy is enhanced by 30% after day-15. Associated with the enhanced secondary circulations is increased zonally averaged precipitation in the summer hemisphere and decreased zonally averaged precipitation in the winter hemisphere in July. In January the precipitation increases in both hemispheres.

The dependence of the wind profile power-law exponent (p) on surface roughness and atmospheric stability is depicted assuming a height variation of p (Huang, 1979; Hanafusa et al., 1986) and using the formulation of Zilitinkevich (1989) for determining the velocity profiles in a neutrally and stably stratified planetary boundary layer. The theoretical estimates of the power-law exponent compare perfectly with the power-law exponent data from various sources and the theoretical analysis from Irwin (1979). It is recognized that more work is necessary before the validity of the suggested methodology can be fully established.

The advection terms in the atmospheric equations of motion will in the spectral domain result in an exchange of available potential and kinetic energies between the various wave numbers. Observational studies have demonstrated that while the available potential energy cascades from lower to higher wave numbers, the kinetic energy is cascaded from the middle wave numbers to both the high and the low wave numbers supposedly due to the fact that the energy conversion from available potential energy to kinetic energy is large in an interval of the wave number scale. The purpose of the present paper is to reproduce some major aspects of these energy cascade processes using first an extremely simple model based on a homogeneous fluid with a free surface. The driving factor in the model is the use of adding and subtracting fluid in such a way that the net addition vanishes. The model will furthermore be restricted to one space dimension in the west-east direction retaining the nonlinearities in the advection terms. The model equations, containing forcing and dissipation, are integrated numerically to a steady state. Evaluations of the energy generation, conversions and dissipations show that the model cascade processes behave correctly with respect to direction and magnitude as compared to the other energy conversions in the model and qualitatively correct compared to observational studies. The second model is based on the primitive equations for the two horizontal wind components and the thermodynamic equation including a specified heating which is independent of time. This model is also treated in the zonal direction only and in wave number space. The model gives good simulations of the transfer of both available potential and kinetic energy as functions of the wave number.