Convective influence and transport pathways controlling the tropical tropopause distribution of carbon monoxide and ozone

Trajectory calculations with convective influence diagnosed from geostationary-satellite cloud measurements are used to evaluate the relative importance of different Tropical Tropopause Layer (TTL) transport pathways for establishing the distribution of carbon monoxide (CO) and ozone at 100 hPa as observed by the Microwave Limb Sounder on board the Aura satellite. Carbon monoxide is a useful tracer for investigating TTL transport and convective influence because the CO lifetime is comparable to the time require for slow ascent through the TTL (a couple of months). Ozone is additionally sensitive to in-mixing to the TTL from the extratropical lower stratosphere. Offline calculations of TTL radiative heating are used to determine the TTL vertical motion field. Convective influence occurrences are diagnosed by tracing the trajectories through geostationary satellite imagery of cloud-top brightness temperature. The simple trajectory model does a reasonable job of reproducing the observed CO and ozone distributions during Boreal wintertime and summertime. The broad winter maximum in CO concentration over the Pacific is primarily a result of the strong radiative heating (indicating upward vertical motion) associated with the abundant TTL cirrus in this region. Sensitivity tests indicate that the distinct CO maximum in the Asian summer monsoon anticyclone is strongly impacted by extreme convective systems with detrainment of polluted air above 360--365 K potential temperature. Ozone abundance at 100 hPa during summertime is strongly sensitive to both isentropic in mixing of high-ozone stratospheric air and upward transport of low-ozone air from the boundary layer and lower TTL. Since TTL heating rates in global chemistry models are necessarily inaccurate because of deficiencies in the global-model cloud representations, the slow ascent pathway through the TTL presents a challenge for simulation in global Eulerian model simulations of TTL ozone abundance.