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

The sensitivity of the surface hydrology to the parameterization scheme incorporated in three different AGCMs is investigated. It is found that the simulations of the surface hydrology by the NCAR CCMO and GFDL models (which incorporate the bucket type hydrological parameterization) differ markedly from the CCM1B model (which incorporates the Biosphere Atmosphere Transfer Scheme, BATS). The AGCMs which incorporate the simpler parameterizations of the land surface simulate a number of physical phenomena unrealistically. Many of these gross problems in the land surface climatology are eliminated in the CCM1B model which incorporates BATS. When present-day and doubled CO2 scenarios are compared, it is shown that the differences between model results incorporating different surface schemes are greater than the differences between 1 x and 2 x CO2. The implications of these results are that the surface hydrological fields from AGCMs, and their predictions of climatic change at the land surface, are likely to be unreliable. Investigations of the impact of climatic change consequent upon changes in the land surface climatology should employ one of the advanced parameterizations of the land surface coupled into the general circulation model, and develop and validate those components of the atmospheric model, such as the surface radiative forcing, regional precipitation patterns and the diurnal cycle within the planetary boundary layer, that are most important for deriving land surface processes.

In this work, the set of annual pluvial precipitation patterns obtained in 57 weather stations from the southern part of baja california peninsula (mexico) during more than 20 yeras is presented. Three distinctic periods are readily recognizable from the annual mean pattern stand point of view, as follows: period I corresponding to the dry season from March to June; period II corresponding to the rainy season from July to October; period III corresponding to the rainy season from November to February. A regionalization was obtained from the rainy regime based on the relative weight of both rainy periods, merked along the mean physiographical climatological zonal features, that in general terms correspond to the climatic zonation obtained by several authors based on different data sets.

The data from six air quality stations in California were subjected to a principal components analysis involving elemental, gas, and meteorological variables. The highly intercorrelated nature of many of the variables can make the results of ordinary regresssion techniques uncertain. The application of principal component analysis to the data set produces statistically independent linear combinations of the original variables. The factor which represents soil-derived particulate matter usually accounts for most of the observed variability. The visibility factor is present at every location and intermediate size sulfur-containing aerosols (sulfur size mode 0.6 µm < Dp < 3.6/µm) are major contributors to visibility reduction at all sites: coastal, urban, and interior valley. The rest of the principal factors were tentatively assigned to automotive pollution, fuel burning, and agricultural burning on the basis of their chemical composition.

Solar radiation data (global and diffuse) provided by the Solar Radiation Observatory of the Institute of Geophysics of the National University of Mexico, corresponding to the period 1980 to 1985, are analyzed. Two sets of data where selected. The first contains all 10 and 11 hours (L.T.) data and the second contains only the values corresponding to maximum insolation (MI), as recorded by a Stokes heliograph. Therefore the influence of clouds is minimized with the second, corresponding to cloud free condition. From the analysis of the annual and monthly averages the effects of El Chichon (1982) are clearly visible in diffuse radiation. The effects of El Nino phenomenon (increases of the surface temperature of the Pacific Ocean) from 1982 to 1983, are apparent in the global radiation averages.

Infrared radiation data for the period 1980-1987 obtained at the Solar Radiation Observatory of the Institute of Geophysics of the National University of Mexico, is analyzed with the help of empirical and theoretical models for the transfer of long wave radiation. Model results and measurements agree for the years of 1980-1982 For later years there are differences between calculations and data, increasing year after year. These results indicate that measurements are not reliable from mid-1982 and on, the reason being that there are no physical causes for a monotonous increase in infrared radiation starting in 1982. Using the good data we have adjusted Swinbank's formula to different seasons (Mexico City), by using different constants. This allows a better determination of the surface fluxes. With these empirical and theoretical formulas we have corrected the data, for the whole period The anomaly of 1982, 1983 (year of El Chichon and El Nino) becomes apparent.

A mesoscale model of the surface wind distribution over complex terrain is described. It is designed to simulate the time as well as the geographical variations of the wind field. The model equations incorporate the effects of nonuniformities in surface temperature, roughness, and terrain elevation. Initial integrations of the model equations have been made to simulate flow patterns in the vicinity of an isolated hill and over coastal regions during the occurrence of a sea breeze. The results of the integrations indicate that the model is potentially useful for studying flow over complex terrain.

A review of the results of studying the role of the biosphere in the climate formation has been made which shows that a new stage of the climate theory development has been started which demonstrates the necessity to take into account biospheric processes. This has been demonstrated by the need to more adequately consider land surface processes as well as by obvious requirements to take into account the interaction between biogeochemical cycles and climate. Various approaches to the consideration of the biosphere as a climate-forming factors have been discussed as well as some results of numerical modelling and possibilities to utilize data of combined surface and satellite observations to determine those parameters which characterize the interaction between the atmosphere and biosphere.

Air temperature data of Belgrade are analysed to point out the variations caused by natural events and human activities. In particular, the influence of the growth of the city on the minimum average temperature is evident.

It has been known for some time that the subtropical Eastern North Pacific Ocean, just west of the coast of Mexico experiences a high incidence of tropical cylone formation. One currently accepted mechanism for tropical cyclone initiation in the Eastern Pacific involves easterly waves that originate over Africa and propagate across the Atlantic. Recent investigations indicate that other mechanisms, such as the interaction of the large scale flow with the topography or the formation of mesoscale convective systems (MCSs), may also be important in initiating tropical cyclones in this region. Infrared satellite imagery is used to illustrate specific examples of the alternative mechanisms described above that occurred during the 1989 hurricane season. Hurricane Lorena and Tropical Storm Manuel appear to have originated from a single region of disturbed weather associated with flow over the Sierra Madres and Tropical Storm Priscilla appears to have formed from an MCS that first appeared over Mexico. Conventional sounding and wind data are used to demostrate that the incident flow present was favorable for the generation of orographic cyclones during the formation of Lorena and Manuel and that the environment was conditioned for MCS formation prior to the development of Priscilla.

A thermodynamic model is used to simulate the annual cycle of the sea surface temperature (SST) in the Gulf of The model includes as the basic equation the thermal energy equation applied to the upper mixed layer of the ocean This equation is vertically integrated and includes the horizontal transport of heat by mean ocean currents and by turbulent eddies, as well as the heating by radiation, sensible heat given off to the atmosphere and evaporation. The thermodynamic model is adapted, by using a regular grid with a distance of 60 km between adjacent points covering the whole area of the Gulf of Mexico. In these numerical experiments the observed surface currents and the horizontal transport of heat through the Yucatan Channel are used as prescribed fields, as well as the atmospheric conditions. An objective comparison of the values of the computed SST with those observed, shows a good agreement.