OUR PRIMARY OBJECTIVE IS TO OBTAIN UNIQUE INFORMATION ABOUT THE NIGHT-TIME STRUCTURE AND DYNAMICS OF THE LOWER ATMOSPHERE THROUGH ANALYSIS OF MARS GLOBAL SURVEYOR (MGS) RADIO OCCULTATION (RO) MEASUREMENTS. WE WILL EXAMINE ABOUT 9400 RO PROFILES IN SEARCH OF NIGHT-TIME LAYERS OF NEUTRAL STABILITY ASSOCIATED WITH WATER ICE CLOUDS AND WE WILL DETERMINE BASIC PROPERTIES OF THESE NOCTURNAL MIXED LAYERS (NMLS) AND CHARACTERIZE THEIR SPATIAL DISTRIBUTION AND SEASONAL EVOLUTION. THE DATA CONSIDERED HERE ARE FROM THE MOST ACTIVE PHASE OF THE ANNUAL WATER CYCLE IN NORTHERN SPRING AND SUMMER (LS = 0-180 DEG) WHEN THE ATMOSPHERE IS RELATIVELY COOL AND MOIST. THESE PROFILES COVER LATITUDES FROM 30S TO 85N PRIMARILY AT LOCAL TIMES OF 3-9 H WITH DENSE SAMPLING IN LONGITUDE. ABOUT 600 PROFILES ARE AVAILABLE IN THE VICINITY OF THE PHOENIX LANDING SITE WHERE NIGHT-TIME CLOUDS WERE OBSERVED BY THE LIDAR INSTRUMENT. A PILOT STUDY DEMONSTRATES THAT NMLS ARE PRESENT IN THESE RO PROFILES AT A VARIETY OF LOCATIONS INCLUDING THE PHOENIX LANDING SITE AND OCCUR FREQUENTLY ENOUGH TO MERIT FURTHER STUDY. NMLS DRAMATICALLY TRANSFORM THE NIGHT-TIME WEATHER AT SOME LOCATIONS MAKING IT FAR MORE INTERESTING AND ENERGETIC THAN IT WAS THOUGHT TO BE. IN ADDITION WE WILL USE A HIGH-RESOLUTION MARS GLOBAL CIRCULATION MODEL (MGCM) AND LARGE EDDY SIMULATION (LES) TO GAIN A DEEPER UNDERSTANDING OF THE RESULTS OBTAINED FROM ANALYSIS OF THE RO PROFILES. GOALS OF THE MODELING EFFORT INCLUDE: (MGCM) TO IDENTIFY AND CHARACTERIZE THE ATMOSPHERIC PROCESSES SUCH AS THERMAL TIDES AND REGIONAL TOPOGRAPHIC CIRCULATIONS THAT CONTROL THE FORMATION OF NOCTURNAL WATER ICE CLOUDS AND TO ACCOUNT FOR THE SPATIAL DISTRIBUTION OF THE CLOUDS AND THEIR EVOLUTION WITH TIME OF DAY AND SEASON; AND (LES) TO ASSESS THE IMPACT OF NMLS ON THE NIGHT-TIME WEATHER AND WATER TRANSPORT IN THE LOWEST SCALE HEIGHT ABOVE THE SURFACE. WATER-ICE CLOUDS VARY BOTH SEASONALLY AND DIURNALLY AND ARE KNOWN TO AFFECT THE GLOBAL TRANSPORT OF WATER VAPOR AND THE ANNUAL WATER CYCLE. THIS INVESTIGATION WILL DRAMATICALLY IMPROVE OUR UNDERSTANDING OF NIGHT-TIME CLOUDS REVEALING ASPECTS OF THEIR SPATIAL DISTRIBUTION SEASONAL EVOLUTION AND IMPACT ON DYNAMICS THAT CANNOT BE OBSERVED BY OTHER TECHNIQUES. WE WILL GAIN NEW INSIGHT INTO ATMOSPHERIC PROCESSES THAT STRONGLY INFLUENCE THE NIGHT-TIME DYNAMICS OF THE LOWER ATMOSPHERE THE DISTRIBUTION OF WATER ICE CLOUDS AND THE TRANSPORT OF WATER THROUGHOUT THE NORTHERN HEMISPHERE KEY ASPECTS OF MARTIAN WEATHER AND CLIMATE.