Overview of atmospheric conditions during the Smoke, Clouds, and Radiation- Brazil (SCAR-B) field experiment

The Smoke, Clouds, and Radiation-Brazil (SCAR-B) field experiment was condu cted in central Brazil and southern Amazonia during the period August 15 to September 20, 1995, This paper presents an overview of atmospheric conditi ons during the SCAR-B period. A meteorological office was established in Br asilia to support the mission flights and field activities. All the meteoro logical data collected during the SCARE have been archived and are availabl e to the scientific community. The meteorological conditions throughout the SCAR-B period of August and September 1995 were near climatological condit ions. Few synoptic-scale waves traveling from southeastern Pacific reached Brazil, therefore the SCAR-B period was characterized by long periods of lo w humidity, dryness, little cloudiness, or rain, and haze events. The stabl e situation was interrupted due to the penetration of a frontal system on S eptember 20, 1995, and a second and more rain-producing one on September 28 , 1995. Those two frontal systems in a period of 10 days brought an end to the dry season. Air particle trajectories show that most of the smoke below 4 km from Amazonia was transported to the south and then to the east exiti ng the continent at 25 degrees S-30 degrees S. Radiative transfer calculati ons carried out for the clear sky gaseous and aerosol atmosphere show the d ecrease of the solar radiation absorption in the atmosphere-surface system due to smoke aerosol loading at the value from 5 to 50 W m(-2) depending on the aerosol optical thickness, single-scattering albedo, and solar zenith angle.