Quantifying Deep Convective Influence on the Tropical Tropopause Layer (TTL)
October 27, 2011
Hosted by Thomas Birner (advisor), Graeme Stephens, Colette Heald, David Krueger (Physics)
The transition between the troposphere and the stratosphere is best described as a layer containing both tropospheric and stratospheric characteristics. In the tropics, this region is known as the Tropical Tropopause Layer (TTL). The TTL roughly spans the altitude range of 12-18 km, bounded from above by the cold point tropopause (CPT) and from below by the main convective outflow level. This region is unique in that it is subject to both tropospheric and stratospheric processes (e.g. deep convective transport/the stratospheric circulation). Processes in the TTL set the boundary condition for atmospheric constituents entering the stratosphere. This thesis aims to better quantify deep convective influence on the TTL using two approaches.
The first approach investigates TTL ozone using the Southern Hemisphere Additional Ozonesondes (SHADOZ) dataset. Low ozone concentrations in the TTL are indicative of deep convective transport from the boundary layer. A new diagnostic, the â€œozone mixing heightâ€ is introduced that identifies the maximum altitude in a vertical ozone profile up to which reduced ozone concentrations, typical of transport from the boundary layer are observed. Deep convective temperature and stratification signals in the TTL are quantified using this diagnostic.
The second approach collocates deep convective clouds identified by CloudSat 2B-CLDCLASS with COSMIC GPS temperature profiles. Results suggest the convective temperature signal is large-scale and persistent in time; however, it is only the convective events that penetrate into the upper half of the TTL that have a significant impact on TTL temperature. Deep convective cloud top heights appear to be well approximated by the level of neutral buoyancy.