Abstract
Abstract. Past studies have identified a variety of pathways by which carbon monoxide (CO) may be transported from the surface to the tropical upper troposphere (UT); however, the relative roles that these transport pathways play in determining the distribution and seasonality of CO in the tropical UT remain unclear. We have developed a method to automate the identification of two pathways ("local convection" and "advection within the lower troposphere (LT) followed by convective vertical transport") involved in CO transport from the surface to the UT. This method is based on the joint application of instantaneous along-track, co-located, A-Train satellite measurements. Using this method, we find that the locations and seasonality of the UT CO maxima in the tropics were strongly correlated with the frequency of local convective transport during 2007. We also find that the "local convection" pathway (convective transport that occurred within a fire region) typically transported significantly more CO to the UT than the "LT advection → convection" pathway (advection of CO within the LT from a fire region to a convective region prior to convective transport). To leading order, the seasonality of CO concentrations in the tropical UT reflected the seasonality of the "local convection" transport pathway during 2007. The UT CO maxima occurred over Central Africa during boreal spring and over South America during austral spring. Occurrence of the "local convection" transport pathway in these two regions also peaked during these seasons. During boreal winter and summer, surface CO emission and convection were located in opposite hemispheres, which limited the effectiveness of transport to the UT. During these seasons, CO transport from the surface to the UT typically occurred via the "LT advection → convection" pathway.
Highlights
Biomass burning and fossil fuel combustion have long been recognized as globally important sources of trace gases and aerosols, especially in the tropics
We have presented a method that provides an automated identification of two pathways that transport Carbon monoxide (CO) from the surface to the upper troposphere (UT) through a joint use of several A-Train satellite measurements
We have shown a case study that demonstrates the effectiveness and validity of this method based on comparison with the results of a back trajectory analysis
Summary
Biomass burning and fossil fuel combustion have long been recognized as globally important sources of trace gases and aerosols, especially in the tropics. Previous studies based on observations and/or modeling (Novelli et al, 1998, 2003; Edwards et al, 2006; Duncan et al, 2007a; Junhua Liu et al, 2010; Macdonald et al, 2011) have shown that CO seasonal and interannual variability in the troposphere is affected by many factors, which can primarily be divided into the categories of photochemistry and transport. These factors vary greatly among different geographic regions
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