Observations of a deep tropopause fold over Darwin during ACTIVE and SCOUT-O3 - Implications for the TTL and local meteorology

The meteorology of the Darwin (Northern Australia) region and the nearby Tiwi Islandsis of particular interest due to the potential influence of frequent deep-convectivestorms on stratosphere-troposphere exchange. Such meteorology and convective transporthas been the subject of intense study during the simultaneous and synergisticACTIVE (Nov 2005 - Feb 2006) and SCOUT-O3 (Nov-Dec 2005) campaigns, whichcombine low and high altitude aircraft measurements over the Darwin and Tiwi Islandregion and includes a series of ozonesondes launched throughout ACTIVE. Inthis paper we discuss ozone soundings recorded from Darwin Airport in Novemberand December 2005 which show evidence for stratosphere-to-troposphere transport ofdry, ozone-rich air over Northern Australia in an unusually deep and unusually placedtropopause fold, both in terms of its geographical location and low latitude, and itsextent into the lower free troposphere. The potential role of such thick layers of dry,ozone-rich air in the free troposphere are investigated here in the context of localand regional convective inhibition and intensity using a large eddy model of so-calledHector island thunderstorms, with a comparison to 3D polarimetric radar observations,as well as available meteorological fields and satellite imagery provided by theAustralian Bureau of Meteorology. In addition to the potential for convective perturbation,the presence of such chemically perturbed layers of air in the free tropospheremay also affect local chemistry, and subsequently the composition and chemistry ofthe TTL by later uplift in deep tropical convection.