Distribution of air mass origins and TTL water vapor during the Fall 2011 ATTREX deployment

Measurements of the Tropical Tropopause Layer (TTL) obtained from the Airborne Tropical TRopopause EXperiment (ATTREX) flights in Oct-Nov 2011 are analyzed to investigate the dynamical and microphysical processes that control water vapor concentrations in the TTL. Air parcels along the flight tracks are run backwards in time using a trajectory model and the resulting diabatic trajectories are combined with time-varying infrared satellite imagery to determine the extent to which the sampled air parcels have been influenced by convection. Backward trajectory and convective influence analyses of the data from Nov 2011 flights show that air parcels at tropical latitudes at the ~100 hPa level have primarily originated in the midlatitudes. Coldest temperatures within a two-week time period were achieved at or near the flight track. Tropical air at ~100 hPa level appears to have experienced minimal convective influence in the recent past, consistent with aircraft measurements of water vapor and other trace species. Convective influence of air parcels is substantially more prominent at lower levels and at regions south of 10ºN.

A one-dimensional Lagrangian cloud model is used to simulate ice cloud formation and dehydration along the trajectories of the sampled air parcels. The large-scale spatial structure and vertical profile of the simulated water vapor mixing ratios averaged over the flight track region in the tropical Pacific are in reasonably good agreement with the aircraft and Microwave Limb Sounder observations. Temperature perturbations by sub-grid scale gravity waves enhance dehydration and result in anomalously dry TTL in the simulation.

Preliminary results from Feb-Mar 2013 ATTREX flights will also be presented.