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

A numerical model of dust storm occurrence during periods of strong prevailing flow over homogeneous terrain is presented. The model, which is time-dependent, includes a prediction of the Earth's surface temperature with the force-restore method. Turbulent mixing along the vertical is incorporated through a second order formulation of turbulent fluxes. The model is used to simulate the occurrence of dust storms over Kuwait in June 1973. The simulation is able to reproduce the observed diurnal variation of dust storms. The model is also used to analyze the dependence of dust storms on the prevailing wind speed as well as on dust particle size. The results of the analysis are described.

Using the filtered baroclinic model of the Center for Atmospheric Sciences of the National University of Mexico, an application to forecast hurricane tracks possibly affecting the Mexican Republic is presented. This application solves the baroclinic equations given by Buendía et al. (1984) over the WMO Region IV using a lattice of 69 X 77 points over a Lambert projection tangent on 30º. The results are favorable and useful for Mexican activities.

For practical applications both the parent distribution of rainfall intensities and the distribution of their annual maxima are of interest. The relation between these two distributions cannot be obtained from classical extreme value theory because of seasonal variation and serial correlation in the data. Mathematical results for the distribution of maxima mm-dependent sequences are given to illustrate the effect of local dependence on the extreme value distribution. The average number of exceedances in a cluster is an important parameter in the relation between the parent and extreme value distribution. For 5-min rainfall data from Belgrade quantities of the annual maxima are overestimated by about 10 mm h-1 if the effect of serial correlation is ignored. This bias can easily be removed by taking local clustering of large rainfall intensities in a rainy spell into account.

Results are presented of a ground based experiment for studying heights, thicknesses, optical properties of cirrus clouds and radiative fluxes. Theoretical studies concerning some diffraction effects, inverse problems of lidar sounding, and construction of optical models of cirrus clouds are described. Calculations of fluxes of solar and thermal radiation, albedo, and radiative balances are performed and compared with experimental data.

We use Fourier analysis and Spiegel's results (1957) to calculate the radiative decay of a small, smooth, localized, temperature perturbation in a homogeneous, isothermal atmosphere, assuming the grey case. We find approximate, analytic expressions for the decay in both the optically thin and optically thick limits. We also derive a method for checking the accuracy of the solution(s) using the conservation of energy of the perturbation.

FForecast errors exhibit the characteristics of approximations in simulating dynamical and physical processes in models. The models are very complex and hence it is not always possible to identify the approximations responsible for any particular error pattern in forecasts. A comparison between the models' forecast performances can be valuable in isolating the causes of error patterns. Here a comparison of forecast errors in the AFGL (Air Force Geophysics Laboratory) and COLA (Center for Ocean-Land-Atmosphere Interactions) models is made with the expectation of identifying the causes of forecast errors. The two models are based on identical approximations in simulating the dynamical processes and only minor differences in parameterizations of the physical processes. Nine ten-day forecasts are made to study the error characteristics in the two models. The errors in the 500 mb geopotential height are negative in tropics and positive in extratropics. The temperatures at 850 mb are colder than observed in tropics and warmer than observed in extratropics. At 150 mb the temperatures are warmer tan observed in tropics and colder than observed in extratropics. These qualitative error characteristics are not only common to these two models, but also to the NMC (National Meteorological Center), GFDL (Geophysical Fluid Dynamics Laboratory), and ECMWF (European Centre for Medium-Range Weather Forecast) forecast models. The difference in the error structure between the two models is the magnitude of the error in the tropics. The tropical error in the AFGL model is larger than that in the COLA model. Another difference is in the 850 mb relative humidity field. In the AFGL model, relative humidity errors are negative largely over the ocean and positive over land with minor exceptions. This error structure differs from that of the COLA model which consists of mostly positive errors everywhere with some small regions of negative errors. The major differences in the physical parameterizations between the two models are in the radiation interaction with deep convective clouds, the manner in which the sea surface temperature (SST) is prescribed and the vertical transport of heat and moisture by shallow convection. The magnitude of tropical errors in the geopotential height at 500 mb and temperature at 850 mb may be because the AFGL model does not include deep convective cloud-radiation interactions. The 850 mb relative humidity errors over oceans are probably due to the manner in which the SST is prescribed and the lack of proper vertical transport of moisture by the shallow convection parameterization.

A low-order, quasi-geostrophic, two-level model is used to investigate the response to external heating. The heating has variations in both south-north and west-east directions. The frictional dissipation is incorporated by using both boundary layer and internal friction. The zonal flow is described by two dependent variables, one for the vertical mean flow and the other for the vertical shear flow. The remaining four dependent variables in the model are the amplitudes of the sine- and cosine-components of a travelling wave in the vertical mean flow and in the vertical shear flow. The low-order model is stable in the sense that trajectories starting outside a certain circle will cross the circle and approach the origin of the six-dimensional space. The model has also the property that the rate of change of a small volume is negative indicating that the small volume will shrink to zero. Any attractor, which may exist, is thus of zero volume. A detailed study of the multiple steady states of the model and their stability is postponed to a later publication. In this study we rely on a number of long-term numerical integrations, which show that the model approaches either a stable, steady state or a periodical time-dependent solution. It appears therefore'that the model does not contain chaotic solutions. Comparisons are made with the three parameter model recently published by Lorenz and with the models developed by Saltzman et al. This Lorenz model, which contain chaotic solutions for sufficiently large south-north external forcing, can be obtained as a special case of the six parameter model. The different behavior of the two models may be explained by the assumptions, which are necessary to obtain the simpler model from the other. It is shown that the Lorenz-model describes the thermal flow of the two-level model, and that the phase difference between the thermal and the mean model flow waves always is a quarter of the wavelength assuring that the south- north transport of sensible heat is at a maximum for given amplitudes. It is also pointed out that large values of the external heating are necessary to obtain chaos in the Lorenz-model. These results are also found in the Saltzman-model, which is a generalization of the Lorenz-model, although both have three dependent variables only. It appears therefore that to explain the inter-annual variations of the atmosphere in terms of chaotic behavior in the cold season and non-chaotic behavior in the warm season will require further investigations using models, which can simulate the cascade processes in the real atmosphere.

Using the solution of a specially formulated adjoint problem an integral formula is derived for the study of linear model response. The formula relates directly every chosen characteristic of the model sensitivity to variations of initial data and forcing. By analogy with the well-known Green function, the adjoint equation solution performs here the role of a weight function (or influence function). A set of such relatively simple formulas gives an effective method for estimating the model sensitivity to different types of input data without solving every time the complicated basic problem. The simplified three-dimensional global heat interaction model of atmosphere and ocean is considered as an example. The model has been linearized by using the climatic monthly mean wind in the atmosphere and the climatic seasonal currents in the World Ocean. The time-space structures of the influence functions calculated for the December mean surface temperature anomalies of the European part of USSR and the USA territory, are demonstrated. The regions of local maxima of the influence function show the energetically active zones in the World Ocean. Within the time intervals while these local maxima exists, only the heat flux anomalies located in such zones can be responsible for the final magnitude of the mean temperature anomaly considered.

Data analysis of relative humidity, barometric pressure, air temperature, radiation, wind speed and wind direction from a metereological station placed at Cayo Arcas, inside of campeche bay, south of the gulf of mexico are presented. observations were made from november 3, 1990 to march 17, 1991. the spectral analysis shows the existence of events with periodicities of 12 and 24 hours for each parameter analysed, which are asociated to a local breeze system. air temperature and radiation series shows additional oscilations at 6 and 8 hours, pressure and wind series present events with additional oscilations at approximatly 4 and 16.6 days, with maximum wind speed of 21 m/s and a predominant direction from the north.

The climatological dat from Tlaxcala state has been used to apply metodologies for soya growing in this state. index related to comfort values for better growing have been claculated, zones with an optimum development and phenological considerations have been chosen. an empirical production biomass model has been applied and the potential of harvesting has been calculated.