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

The asymptotic behaviour of Adem's model is analyzed as a function of the external forcing and the dissipation coefficient. The existence of a bounded attracting set of the sea surface temperature anomalies in a neighborhood of zero is proved. It is shown that the perturbation solution decays exponentially to zero, under a certain condition. The decay rate depends on the external forcing and the turbulent coefficient.

The correctness of the adjoint approach used in Marchuk and Skiba (1992) is demonstrated. Remarks are made on the historical development of the adjoint methods and its application in the works by Cacuci (1981), Cacuci and Schlesinger (1993), Hall (1986), Hall and Cacuci (1983) and Hall et at. (1982).

A revised version of the Adem Thermodynamic Model is used to make mean monthly predictions of temperature and precipitation anomalies in the Northern Hemisphere. The initialization data are the sea surface and 700 mb temperatures in the previous month. Predictions for the period December 1981 to November 1983 were carried out and verified over the Mexican Republic. The results show some skill in the prediction of temperature and precipitation anomalies. The experiments show that the ocean temperatures play an important role in the predictions, and it may be suggested that above normal temperatures in the near Pacific Ocean regions and in the Gulf of Mexico may produce below normal precipitation anomalies in Mexico and possibly favour a drought situation. Sensitivity experiments on the change of surface albedo due to changes in vegetation, show important regional variations in temperature and precipitation and therefore, suggest the necessity of its incorporation in the model for monthly climate prediction in this region.A DRUOGHT

A heuristic theory of the zonally averaged structure of the atmosphere is formulated on the spherical Earth using parameterization of the influence of the eddies on the zonal structure. The principal influences of the eddies are the meridional transports of heat and momentum. These transports are expressed in terms of zonally averaged quantities by using the assumption that the transports of quasi-conservative quantities may be parameterized by a diffusion process with a constant value of the coefficient. The principle is used on the transports of potential vorticity and of potential temperature, where after it is shown that the momentum transport may be obtained indirectly. The theory is formulated for the quasi-geostrophic two-level model with heating and dissipation using an expansion of the dependent zonally averaged variables in Legendre polynomials. The quasi-geostrophic equations supplemented by a linear balance equation are sufficient to satisfy the parity relations valid on the sphere. Applications of the theory are carried out using zonally averaged heating based on calculations from observations or on simple specifications. In the first case it is shown that the theory, in a qualitatively correct way, can account for the meridional profiles of the zonal winds at the various levels, for the mean meridional circulation and for the meridional transports of momentum derived from the meridional transport of vorticity. Solutions for various values of the coefficient determining the transport of potential vorticity show that the energy conversion from eddy to zonal kinetic energy is particularly sensitive to the strength of the potential vorticity transport. If the transport is decreased, it turns out that the conversion becomes negative in such a way that the conversion goes from the zonal to the eddy kinetic energy. It is known that this situation corresponds to intense cases of blocking. A simple specification of the heating, simulating heating in the lower and cooling in the higher latitudes is insufficient to give a qualitatively correct picture of the mean meridional circulation.

The observed global, hemispheric, and meridional (zonal means) temperature fluctuations near surface covering the period 1851-1991 or 1861-1991, respectively, are reproduced by 'multiforced' regression models which take into account volcanic, solar, ENSO, and GHG (greenhouse gases) forcing. Moreover, the observed trends and trend-to-noise ratios are compared using different data sources. Different statistical tests including random forcing of detrended data (Monte Carlo testing) and extrapolations on the basis of 'calibration' subperiods demonstrate that the statistical approach works quite well Therefore not only assessments of GHG and natural signals in observational temperature time series are presented but also extrapolations based on the IPCC scenarios A and D. A comparison with the results obtained from the Hamburg Max-Planck-Institute for Meteorology (MPI) coupled atmosphere-ocean transient simulations show a somewhat larger magnitude of the statistically derived GHG signals where the difference, however, is not significant when the uncertainties of both methods are taken into account.

This paper shows the effect of El Niño/Southern Oscillation (ENSO) on the mid-summer drought at Veracruz state. To analyze this effect we compared the average monthly precipitation of the years with El Niño and that for not El Niño years of 51 climatological stations. The period of record for each station varied from 25 to 75 years. The results show that during the event El Niño the mid-summer drought is diminished or disappeared in almost all the Veracruz state. This occurs during the months of July and August. However, on the highlands of central Veracruz the intensity of mid-summer drought is incremented. Finally we applied the variance comparison test of Fisher to know if the variation of the precipitation in July and August was random or originated from El Niño. The statistical analysis shows that the variation of the precipitation in some regions of Veracruz states is significant from .1 to 5.  

Sulfur emissions and sulfate concentrations in ice samples obtained from different depths at a site in Southern Greenland are used to infer a relationship between the emissions and sulfate aerosols. In a theoretical model, it was found that this relationship is nonlinear. The upward trend in the sulfate concentrations over the past 100 years is related to a change in cloud droplet concentrations and its impact on global surface temperature. It is estimated that 1.0 to 2ºC of cooling is possible.

In this paper we examine measurements of the thickness of the total ozone column between 1986 and 1989 in Mexico City. We consider the contribution of the surface ozone in measurements of the total ozone column made with the Dobson Spectrophotometer located at the Solar Radiation Laboratory (National University), in the southwest of Mexico City. We consider different depths of the mixing layer depending on the season and we compare our results with those reported for Mauna Loa in Hawaii and Poona in India, at the same latitude as Mexico City. In conclusion we confirm that in highly polluted areas the surface ozone has an important effect on measurements of the total ozone column.

A numerical model for studying the development of sea breeze rainfall in the vicinity of a straight coastline is described. The model is based on the time-dependent primitive equations. The model is able to describe explicitly the formation of rain and its subsequent space and time variations. The description is done by incorporating a prediction equation for rain water which is derived through a parameterization of cloud microphysical processes. An initial test of the model is done by simulating the sea breeze rainfall for a case of no prevailing flow during the rainy season in the tropics. In general, the simulation reproduces the observed characteristics of sea breeze rainfall. The sensitivity of the model to the cloud microphysical parameterization constants associated with autoconversion and accretion is investigated by means of numerical experiments. The experiments show that the rainfall is relatively insensitive to the autoconversion model constants but quite sensitive to the accretion constant.

Semi-empirical and theoretical formulations which have been proposed to describe the transition-layer mean wind-speed profiles (Zoumakis, 1992c; 1993c; 1993d; 1994) are used to derive relationships between the roughness length zo, zero-plane displacement d, and transition-layer depth z*, and to estimate the diffusivity coefficients K of turbulence transfer mechanisms within and above tall vegetation and forest canopies. The theoretical estimates of d, z* and K compare well with data from various sources and the theoretical analysis from Thorn (1971), Landsberg and Jarvis (1973), Bache (1986) and Zoumakis (1994).