Field observations and numerical studies revealed that large scale deforestation in Amazonia could alter the regional climate significantly, projecting a warmer and somewhat drier post‐deforestation climate. In this study we employed the CPTEC‐INPE AGCM to assess the effects of Amazonian deforestation on the regional climate, using simulated land cover maps from a business‐as‐usual scenario of future deforestation in which the rainforest was gradually replaced by degraded pasture or by soybean cropland. The results for eastern Amazonia, where changes in land cover are expected to be larger, show increase in near‐surface air temperature, and decrease in evapotranspiration and precipitation, which occurs mainly during the dry season. The relationship between precipitation and deforestation shows an accelerating decrease of rainfall for increasing deforestation for both classes of land use conversions. Continued expansion of cropland in Amazonia is possible and may have important consequences for the sustainability of the region's remaining natural vegetation.

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The Center for Weather Forecasting and Climate Studies-Center for Ocean-Land-Atmosphere Studies (CPTEC-COLA) atmospheric general circulation model (AGCM) is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the model's performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern portions and underestimates it in the northern portions of these systems. The high-and low-level main circulation features such as the subtropical highs, subtropical jet streams, and storm tracks are depicted well by the model, albeit with different intensities from the reanalysis. The stationary waves of the Northern and Southern Hemispheres are weaker in the model; however, the dominant wavenumbers are similar to the observations. The energy budget analysis shows values of some radiative fluxes that are close to observations, but the unbalanced fluxes in the atmosphere and at the surface indicate that the radiation and cloud scheme parameterizations need to be improved. Besides these improvements, changes in the convection scheme and higher horizontal resolution to represent orographic effects better are being planned to improve the model's performance.

The authors investigate one case of surges of polar air that occasionally propagate into southeastern Brazil during wintertime and are harmful to coffee production because of the freezing conditions associated with them. The cooling is also observed in southern and, with less intensity, in western Amazonia. The event of 26 June 1994 is studied. The frost event caused a sharp drop in coffee production and similarly dramatic increases in coffee prices.The event was characterized by the presence of an anticyclonic perturbation off the coast of Chile that enters South America and crosses the Andes Mountains south of 45ЊS hours later. The anticyclone center tracks equatorward until it reaches 20Њ-30ЊS and then shifts eastward toward the Atlantic.Based on a diagnostic analysis using the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis, a two-stage process can be distinguished. In the starting period, midtropospheric troughing is established east of the Andes, over central Argentina, due to stretching and/or vorticity advection. This troughing is responsible for cold advection along the eastern flank of the Andes, which produces substantial temperature drops and deepens the upper trough locally. The increase in the magnitude of the zonal temperature gradients east of the cold advection zone at levels near 700 hPa is another result of the cooling process. This feature would ensure that the cold advection be extended eastward, producing an upper-level trough local deepening there. This intensification would produce an increase in the cyclonic vorticity advection, which would tend to produce sea level pressure drops underneath. This near-surface low pressure area would eventually contribute to the southeastern Brazil (SB) cooling due to the associated southerly winds.Another feature is the near-surface local anticyclonic generation due to midtropospheric cold advection associated with descending motions, low-level divergence, and anticyclonic growth. Eventually this high pressure would also contribute to produce southwesterlies to transport cold air to SB.The paper is divided in two sections. The first part is a study of synoptic and climatic aspects of the cold surge episodes by using daily surface climatic observations. The purpose of the second part is to analyze the dynamic aspects of this cold episode and to study the cooling mechanisms by using the four-times-daily surface and upper-air NCEP-NCAR reanalysis, as well as to look for possible predictors.

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