Large-scale equatorward transport of ozone in the subtropical lower stratosphere

Anomalous vertical profiles of ozone were observed in the subtropical lower stratosphere (near south Florida) in July 2002 during the NASA-sponsored Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment measurement campaign. It is shown that there is an enhancement of ozone (initially >150%) above the tropopause extending up to ~410 K potential temperature. This ozone increase is the result of recent transport of middle-and high-latitude lower stratospheric air into the subtropics. This meridional transport was a consequence of a geostrophic flow pattern established by a quasi-stationary anticyclone centered over the south central United States that persisted for much of July 2002. We show the spatial and temporal extent of meridional isentropic transport into the subtropics by examining the ozone vertical profiles in combination with the NOy:O3 correlations as well as isentropic back trajectory calculations. The anomalous ozone profiles are also reproduced in a global chemical transport model.