THE NASA A-TRAIN CONSTELLATION S CALIPSO CLOUDSAT AND AURA SATELLITES PROVIDE AN IDEAL PLATFORM FOR EXPLORING THE RELATIONSHIPS BETWEEN TROPICAL CIRRUS AND STRATOSPHERIC WATER VAPOR. USING A-TRAIN OBSERVATIONS THIS STUDY WILL INVESTIGATE THE ROLE OF CIRRUS RADIATIVE HEATING IN MODULATING THE AMOUNT OF WATER VAPOR ENTERING THE STRATOSPHERE. THIN TROPICAL CIRRUS CLOUDS WITH LONG LIFETIMES AND LARGE SPATIAL EXTENT ARE SUSTAINED BY A DELICATE BALANCE OF DYNAMICS AND RADIATION AND IT IS SPECULATED THEY DEHYDRATE THE AIR ENTERING THE STRATOSPHERE IN THE UPWELLING BRANCH OF THE BREWER-DOBSON CIRCULATION. WE WILL EXPLORE THIS PROPOSED MECHANISM THROUGH ANALYZING HOW RADIATIVE HEATING IMPACTS CLOUD PROPERTIES ICE SEDIMENTATION AND THE WATER VAPOR ENTERING THE STRATOSPHERE. THIS STUDY WILL ADVANCE OUR UNDERSTANDING OF STRATOSPHERE-TROPOSPHERE EXCHANGE WHICH IS NECESSARY FOR IMPROVING OUR ABILITY TO MODEL THE STRATOSPHERIC RESPONSE AND FEEDBACK TO A CHANGING CLIMATE.