Boundary layer aerosol and trace gas climatologies from ACTIVE

The Aerosol and Chemical Transport in tropIcal conVEction (ACTIVE) aircraft campaignwas conducted from November 2005 to February 2006 from Darwin, Australia,to characterise the influence of both monsoonal and localised deep convection in thesurrounding maritime and land environment, in determining the composition of theTropical Tropopause Layer (TTL). Aircraft and ozonesonde field measurements weretaken in two phases - the first in November/December 2005 to study pre-monsoondeep convection (so-called Hector storms over the Tiwi Islands off the northern coast)and the second in January/February 2006 to study monsoon convection. In both phasesACTIVE collaborated with two other simultaneous international campaigns at Darwin- the EU SCOUT-O3 project in November/December and the US/Australian TWP-ICEproject during the monsoon period. For ACTIVE, the high altitude Australian Egrettaircraft and lower altitude NERC Airborne Research and Survey Facility (ARSF),Dornier-228 aircraft were employed to measure chemical and aerosol species in theinflow and outflow of tropical storms. This paper discusses the inflow climatology ofsuch species, which include aerosol size and composition, CO, O3, VOCs and CFCs,measured at low altitude (less than 10000 ft) by the Dornier as a function of the evolvinglocal and regional meteorology. The chemical and aerosol background is seen tobe strongly delineated by changes in the prevailing meteorology, as well as by singularevents such as the influence of inland biomass burning. In general, we observe fourcontrasting periods to the background convective inflow: the first of which consists of arelatively polluted and highly variable biomass-burning period throughout November,followed by a second, less variable, moderately polluted phase throughout December,characterised by regular deep convection in the afternoon over the Tiwi Islands andfrequent large-scale squall lines over the Darwin area in both cases. The third and forthphases include a very clean active (and inactive) monsoon period throughout Januaryand a monsoon break period in February, during which the boundary layer backgroundshows a slow return to a more pre-monsoon state. The climatologies presented herewill provide a useful dataset of the Darwin region and a valuable resource for modelsimulation of chemical and aerosol transport by deep convection in the region, andhence links to improved understanding of TTL composition and dynamics.