P. L. Silva Dias

Toward a Unified View of the American Monsoon Systems

An important goal of the Climate Variability and Predictability (CLIVAR) research on the American monsoon systems is to determine the sources and limits of predictability of warm season precipitation, with emphasis on weekly to interannual time scales. This paper reviews recent progress in the understanding of the American monsoon systems and identifies some of the future challenges that remain to improve warm season climate prediction. Much of the recent progress is derived from complementary international programs in North and South America, namely, the North American Monsoon Experiment (NAME) and the Monsoon Experiment South America (MESA), with the following common objectives: 1) to understand the key components of the American monsoon systems and their variability, 2) to determine the role of these systems in the global water cycle, 3) to improve observational datasets, and 4) to improve simulation and monthly-to-seasonal prediction of the monsoons and regional water resources. Among the recent observational advances highlighted in this paper are new insights into moisture transport processes, description of the structure and variability of the South American low-level jet, and resolution of the diurnal cycle of precipitation in the core monsoon regions. NAME and MESA are also driving major efforts in model development and hydrologic applications. Incorporated into the postfield phases of these projects are assessments of atmosphere–land surface interactions and model-based climate predictability experiments. As CLIVAR research on American monsoon systems evolves, a unified view of the climatic processes modulating continental warm season precipitation is beginning to emerge.

THE SOUTH AMERICAN LOW-LEVEL JET EXPERIMENT

Abstract Moisture is transported in South America westward from the tropical Atlantic Ocean to the Amazon basin, and then southward toward the extratropics. A regional intensification of this circulation to the east of the Andes Mountains is called the South American low-level jet (SALLJ), with the strongest winds found over eastern Bolivia. SALLJ is present all year and channels moisture to the La Plata basin, which is analogous to the better-known Amazon basin in terms of its biological and habitat diversity, and far exceeds the latter in its economic importance to southern and central South America in terms of hydroelectricity and food production. The relatively small SALLJ spatial scale (compared with the density of the available sounding network) has a limited understanding of and modeling capability for any variations in the SALLJ intensity and structure as well as its possible relationship to downstream rainfall. The SALLJ Experiment (SALLJEX), aimed at describing many aspects of SALLJ, was carried...

A convective kinematic trajectory technique for low-resolution atmospheric models

This paper presents a simple methodology to take into account the subgrid effects of wet convective processes to trace vertical motion of air parcels for low-resolution atmospheric models. Such models are used for wind field simulations that serve as input for trajectory models. Air parcels in moist convective regions can thus be vertically transported to the cumulus top level with the short timescale associated with cumulus updrafts. Two cases are presented: wet and dry seasons in Amazonia, showing the differences of trajectories followed by air parcels with and without the methodology. The implications for the interpretation of air chemistry measurements are discussed, and an example using LBA/CLAIRE data is used to point out the usefulness of the convective kinematic trajectory technique presented here.

Emissões de queimadas em ecossistemas da América do Sul

THE VEGETATION fires in tropical areas of the Earth are important sources of pollutants to the atmosphere. In South America, during the winter months, an area, mainly of cerrado and forest ecosystems, of approximately 40 thousand square kilometers is burned annually. The biomass burning occurs primarily in Amazon and Central of Brazil regions, but through atmospheric transport these emissions results in a spatial distribution of smoke over an extent area, of about 4-5 millions of square kilometers, much higher than the area where the fires are concentrated. During the combustion process are emitted to the atmosphere gases pollutants and aerosol particles that interact efficiently with radiation, microphysics process, dynamic of cloud formation and the air quality. The effects of these emissions exceed, therefore, the local scale and affect regionally the composition and physical and chemical properties of the South America atmosphere and neighborhood oceanic areas, with potential impact in a global scale.