THE OVERALL GOAL OF THIS PROPOSAL IS TO STUDY THE TIME-DEPENDENT NEUTRAL CHEMISTRY AND TRANSPORT OF WATER IN THE MESOSPHERE AND LOWER THERMOSPHERE (MLT) AND TO DETERMINE THE RESULTANT IMPACT ON THE LOCAL TEMPERATURE AND ICE CLOUD FORMATION. TO REACH THIS GOAL WE WILL ANSWER THREE SCIENCE QUESTIONS: 1. WHAT IS THE ENERGETIC AND CHEMICAL RESPONSE OF THE UPPER MESOSPHERE AND LOWER THERMOSPHERE TO WATER DEPOSITED IN THE LOWER THERMOSPHERE? 2. HOW DOES THE INJECTION OF LARGE AMOUNTS OF WATER VAPOR CHANGE THE THERMODYNAMICS AND IMPACT THE PHYSICS OF PMC FORMATION? 3. HOW IS THE WATER VAPOR THAT GETS INJECTED INTO THE LOWER THERMOSPHERE REDISTRIBUTED VERTICALLY TO THE PMC REGION NEAR 82 KM?