WE PROPOSE TO (1) STUDY MICROPHYSICAL PROCESSES THAT CONTROL WATER AND CLOUDS IN THE UTLS PARTICULARLY THE IMPACT ON AEROSOL ABUNDANCE (2) DETERMINE THE ROLE OF CONVECTION IN GENERATING CIRRUS AND MOISTENING THE LOWER STRATOSPHERE AND (3) QUANTIFY THE WATER BUDGET OF THE LOWERMOST STRATOSPHERE. OUR ANALYSIS WILL USE OUR DOMAIN-FILLING FORWARD-TRAJECTORY MODEL OUR CLOUD MODEL AND OUR NEW BACK-TRAJECTORY MODEL ALONG WITH OBSERVATIONS FROM AURA OTHER SATELLITES AND SUB-ORBITAL MISSIONS. THE RESULTS FROM THIS PROPOSED INVESTIGATION WILL IMPROVE OUR UNDERSTANDING OF TTL AND LOWERMOST STRATOSPHERIC PROCESSES. THIS IS A LONG-STANDING GOAL OF NASA AND WILL HELP IMPROVE CIRRUS PARAMETERIZATIONS AND OTHER IMPORTANT PROCESSES IN CLIMATE MODELS AND ALLOW US TO BETTER INTERPRET NASA SATELLITE AND SUBORBITAL OBSERVATIONS. THIS PROPOSAL CONTINUES OUR RESEARCH ON TTL AND LOWER STRATOSPHERIC WATER VAPOR AND CLOUD AND BUILDS ON OUR EXTENSIVE EXPERIENCE COMBINING OBSERVATIONS AND MODELS TO BETTER UNDERSTAND THE ATMOSPHERE. THE PROPOSED MODELING TOOLS ARE MATURE PUBLISHED AND IDEALLY SUITED FOR ADDRESSING OUR SCIENCE QUESTIONS.