Abstract
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 high‐resolution, 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.
Highlights
Title 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
[1] 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
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
Summary
[4] The occasionally relatively polluted nature of the South Pacific had been discovered long before PEMTropics A, but the evidence apparently had been ignored, perhaps because contamination had seemed so improbable. Allen et al [1996] very clearly show a large southern global plume of carbon monoxide, but previous works do not concentrate on meteorology of its origin, nor do they make extensive comparisons to remote free-tropospheric observations. Clear indications that export of CO from South America and Africa would affect the Southern Ocean were visible in the mesoscale-synoptic model of Chatfield et al [1998] and other work We used this available model at a greatly expanded domain, but finer resolution, to understand features of the global plume. [10] The discussion turns to a statistical analysis and to some thoughts about the limitations of current simulation ability This tracer analysis may have some implications for more complete models attempting to simulate the global tropospheric chemistry of ozone and oxidants [Roelofs et al, 1997; Hauglustaine et al, 1998]
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