Looking Down the Tail Pipe of North America: A Case Study for the Use of Offshore Towers to Constrain the North American Carbon Budget

Prevailing West to East winds across the North American continent suggest that differences in atmospheric carbon dioxide concentrations between air coming onto the West Coast and the air leaving the East Coast will provide a unique constraint on the North American carbon budget. In pursuit of this constraint it has been proposed that a fence comprised of aircraft and tower sites be placed around the perimeter of North America. The offshore tower is particularly appealing as a "fence post" because the local influence of the surrounding water is very small relative to the synoptic influence of air masses coming either from distant land sources and sinks or from the marine boundary layer. This is demonstrated by comparing atmospheric CO2 measurements made at the Martha's Vineyard tower with those estimated by CarbonTracker during winter months. We consider small-scale events like land-sea breezes to understand why summertime comparisons with CarbonTracker are not as good. Comparison with transport fields in CarbonTracker do not indicate that land-sea breezes are the reason for the poor fit.