Tropical ozone as an indicator of deep convection

Abstract

The climatological ozone profile in the tropics is shaped like an “S,” with a minimum at the surface, a maximum at 330 K (∼6.5 km), another minimum at 345 K (∼11.2 km), and a subsequent increase toward the tropopause. These features can be reproduced by a very simple model whose only free parameter is the mean ozone mixing ratio of air detraining from deep convective clouds. To first order, the climatological ozone profile in the tropics arises from a balance between vertical advection, deep convection, and chemistry. The 345 K ozone minimum is coincident with a lapse rate minimum. Both minima are associated with a large increase in convective outflow at 345 K followed by a quasi-exponential decrease. The increase in ozone above 345 K is caused mainly by decreased injection of low-ozone air from the boundary layer. The model tends to underestimate ozone between 340 and 365 K (∼9–15 km). This is most likely due either to an underestimate by the model of in situ ozone production or to eddy transport of ozone from the lowermost stratosphere into the upper tropical troposphere across the subtropical jet. The magnitudes of both these processes are poorly constrained by measurements. In the case of ozone production this is mainly due to a lack of measurements of HOₓ precursors such as acetone and CH₃OOH between 11 and 16 km.