MARCH 2003: Interannual variability of transport pathways for Asian combustion outflow

This figure shows GEOS-CHEM simulated monthly mean horizontal fluxes of Asian anthropogenic CO, integrated over the boundary layer (1000-700hPa) for March of 1994 (weak El Nino, PEM-West B), 1998 (El Nino), 2000 (La Nina), and 2001 (La Nina, TRACE-P). Boundary layer outflow over the western Pacific is largely devoid of biomass burning influence. We find that the dominant outflow pathways are similar for all years but there is some interannual variability related to ENSO. El Nino conditions are associated with a weakened Siberian high, a lower frequency of cold surges, and suppressed convection over Southeast Asia. Spring 2001 (TRACE-P) experienced unusually strong convection in Southeast Asia with associated lifting of biomass burning effluents to the upper troposphere, and an unusually high frequency of cold surges which led to much stronger boundary layer outflow of Asian pollution than in 1994 (PEM-West B). This work was led by Hongyu Liu and a full account is given in Liu et al. [2002b].