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The subtropical global plume in the Pacific Exploratory Mission-Tropics A (PEM-Tropics A), PEM-Tropics B, and the Global Atmospheric Sampling Program (GASP): How tropical emissions affect the remote Pacific


An extended southern subtropical plume of CO meanders > 15,000 km around the world, gradually spreading around ̃20 S. This southern pollution plume is most noticeable in the burning season, southern spring; a similar subtropical plume appears in the northern spring. We use tracer maps to guide the use of trajectories to trace observations of the plume to their origins. The MM5 mesoscale model provides highresolution, near-global synoptic reconstructions of the weather. Two situations are analyzed: NASA's airborne Pacific Exploratory Mission-Tropics A (PEM-Tropics A) period, September-October 1996 and the PEM-Tropics B period, March-April 1999. Similar features are noted for a much earlier mission in 1977, which apparently captured the first, but never-recognized, samples of the global pollution of the Southern Hemisphere. For PEM-Tropics A, near-source pieces of the plume are clearly seen in the Total Ozone Mapping Spectrometer (TOMS) absorbing aerosol product and are well simulated. Downwind, the aircraft sampling of several strands deriving from a single plume seems representative and well simulated. A general mechanism of the plume emerges: The southern plume arises in surface accumulation regions in Africa and South America. Thunderstorm-scale venting of pollutants usually lofts the plume; however, synoptic-scale lifting can produce intense outbreaks. The plume flows eastward in the subtropical jet region as a single coherent but articulated current until it is increasingly filamented by storms in the Pacific. A similar northern subtropical plume is described for the PEM-Tropics B period. The 100-km model resolution we used seemed to capture much of the variability. However, the model somewhat under predicted the highest values. Copyright 2002 by the American Geophysical Union.

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