The nasa airborne tropical tropopause experiment: High-altitude aircraft measurements in the tropical western pacific

The National Aeronautics and Space Administra tion (NASA) Airborne Tropical Tropopause Ex- periment (ATTREX) was a 5-yr airborne science program focused on the physical processes occurring in the tropical tropopause layer (TTL). The 2014 ATTREX deployment to Guam has provided a unique dataset of highly resolved tracer, cloud, water vapor, chemical radical, and radiation measurements in the western Pacific tropical tropopause layer. The winter-time western Pacific TTL is particularly important for controlling stratospheric composition because the coldest tropopause temperatures and strongest vertical ascent rates occur in this region. The ATTREX measurements are being used for two general types of analyses, phenomenological studies focused on understanding particular physical processes such as TTL transport pathways and rates, ice cloud formation and dehydra�tion, dynamics controlling TTL thermal structure, and transport and chemical processes controlling halogen species concentrations; and evaluation and improvement of global-model representations of these TTL processes. The ATTREX measurement suite included tracers with maritime, industrial, biomass-burning, and Southern Hemisphere sources. The unprecedented accuracy and precision of the water vapor measurements permits quantitative investigations of cloud processes such as ice nucleation, crystal growth, sedimentation, and removal of vapor in excess of saturation. Although the ATTREX measurements have provided an invaluable dataset for studying TTL physical processes, a number of key measurement needs remain. Operational limits prevented the Global Hawk from sampling regions with temperatures colder than about 186 K. Trajectory calculations indicate that most air parcels transiting through the TTL during boreal wintertime experience colder temperatures.