The tropical upper troposphere and lower stratosphere (UTLS) plays an important role in the earth's climate, through widespread cloud cover and the regulation of stratospheric humidity. The UTLS is difficult to observe and model because of the wide variety of scales and processes at work there, from aerosols that serve as ice nuclei to global-scale dynamics that drive the Brewer-Dobson circulation. Recent laboratory studies, field experiments and remote sensing observations have advanced our understanding of cirrus and the UTLS, while advances in computation have made possible models that span the range of global to cloud scales. We welcome abstracts that investigate the processes at work in clouds, water vapor and chemistry within the UTLS, as well as those that explore the climate impacts of these processes.