THE RESPONSE OF LOW CLOUDS TO CHANGING ATMOSPHERIC COMPOSITION LIMITS OUR KNOWLEDGE OF BOTH CLIMATE SENSITIVITY AND AEROSOL FORCING. OUR PREVIOUS WORK HAS SHOWN THAT ON TIMESCALES OF A MONTH OR MORE THERE IS A REMARKABLY TIGHT BUT NONLINEAR RELATIONSHIP BETWEEN CLOUD COVER AND ALBEDO. SPATIOTEMPORAL VARIABILITY IN CLOUD COVER CONDENSATE AND EFFECTIVE RADIUS ALL CONTRIBUTE TO LATITUDINAL ALBEDO VARIABILITY BUT THE RELATIVE IMPORTANCE OF EACH IS POORLY QUANTIFIED. CLOUD STRUCTURAL AND RADIATIVE PROPERTIES ARE SHAPED BOTH BY PROCESSES INTERNAL TO THE PLANETARY BOUNDARY LAYER (PBL) AND EXTERNAL CONTROLS. IN PREVIOUS WORK WE DEVELOPED A NOVEL LAGRANGIAN METHOD TO ISOLATE FACTORS CONTROLLING LOW CLOUD VARIABILITY ON PROCESS TIMESCALES. TEMPORAL TRANSITIONS IN LOW CLOUDINESS OFTEN OCCUR RAPIDLY: THE DECORRELATION TIMESCALE FOR CLOUD IS ~18 HOURS. DRIZZLE EXERTS AN IMPORTANT DIABATIC FORCING ON LOW CLOUDS. WE HAVE SHOWN THAT INCREASED DRIZZLE CAN SLOW PBL DEEPENING THOUGH THE EFFECTS OF PRECIPITATION ON CLOUD LIFETIME LIKELY DEPEND ON METEOROLOGICAL STATE. TRANSITIONS IN MARINE LOW CLOUD PROPERTIES OCCUR ON PROCESS TIMESCALES BUT COLLECTIVELY SHAPE THE CLIMATOLOGICAL GEOGRAPHICAL DISTRIBUTION OF ALBEDO FROM THE TROPICS TO THE MIDLATITUDES. RECENT WORK HAS HIGHLIGHTED A MAJOR CONTRIBUTION OF THIN LOW CLOUDS (ALBEDO: ~0.2) TO TROPICAL CLOUD COVER WHICH MAY HELP EXPLAIN THE NONLINEAR RELATIONSHIP BETWEEN CLOUD COVER AND ALBEDO. OPTICALLY THIN LOW CLOUDS ARE TYPICALLY FOUND IN THE UPPER PART OF THE PBL OCCUR FREQUENTLY IN PRECIPITATING MESOSCALE CLUSTERS AND FREQUENTLY CONTAIN LARGE DROPS INDICATING LOW CLOUD DROPLET CONCENTRATION (ND) CONSISTENT WITH STRONG CONTROLS ON AEROSOL BY PRECIPITATION. REMOVAL OF AEROSOL BY COLLISION-COALESCENCE IN DRIZZLING CUMULI OCCURRING IN DEEP PBLS APPEARS TO BE A KEY DETERMINANT OF ND AND THIS IS EXPECTED TO IMPACT REGIONAL ALBEDO. LITTLE IS KNOWN ABOUT WHAT SETS CLOUD COVER AND LONGEVITY OF PRECIPITATING PBL CLOUD SYSTEMS. THE PROPOSED WORK FOCUSES UPON GAINING FUNDAMENTAL UNDERSTANDING OF THE SPATIAL AND TEMPORAL RELATIONSHIPS BETWEEN PRECIPITATION MICROPHYSICS AND CLOUD RADIATIVE PROPERTIES. METHODS/TECHNIQUES: WE MAKE USE OF DATA FROM CLOUDSAT CALIPSO AND OTHER A-TRAIN SENSORS (AMSR MODIS) AND GEOSTATIONARY IMAGERS. WE HAVE DEVELOPED A TECHNIQUE TO USE THE CLOUD PROFILING RADAR ON CLOUDSAT TO TUNE WARM RAIN ESTIMATES FROM AMSR'S 89 GHZ CHANNEL. THE RESULTING TWO-DIMENSIONAL FIELDS OF RAIN RATE (A) ALLOW EXPLORATION OF THE LINKS BETWEEN THE MESOSCALE SPATIAL DISTRIBUTION OF PRECIPITATION AND CLOUD PROPERTIES; (B) PROVIDE CONSTRAINTS FOR LARGE-SCALE NUMERICAL MODELS WHICH POORLY REPRESENT WARM RAIN. THE CALIOP SURFACE RETURN PROVIDES A CONSTRAINT ON OPTICALLY THIN LOW CLOUD WHICH IS USED TOGETHER WITH MODIS CLOUD PROPERTY RETRIEVALS TO CONSTRAIN THE DISTRIBUTION OF CLOUD OPTICAL THICKNESS THUS ALLOWING EXPLORATION OF HOW PRECIPITATION SHAPES BOTH CLOUD MESOSCALE VARIABILITY AND ND. CALIPSO IS USED WITH MODIS TO CONSTRAIN PBL DEPTH. THE HIGH TIME RESOLUTION PROVIDED BY GEOSTATIONARY SATELLITES IS COMBINED WITH ACTIVE SENSORS AND REANALYSIS WITHIN A LAGRANGIAN FRAMEWORK TO EXPLORE THE TEMPORAL EVOLUTION OF PRECIPITATING LOW CLOUD SYSTEMS AND THEIR CONTROLLING FACTORS ON HOURLY TIMESCALES. PERCEIVED SIGNIFICANCE OF THE WORK TO BE PROPOSED: LOW CLOUDS ARE CRITICAL FOR EARTH S ALBEDO AND ULTIMATELY ITS HABITABILITY. OUR PROPOSED WORK EXPLORES COUPLINGS BETWEEN PROCESSES INTERNAL TO THE PBL SUCH AS CLOUD MESOSCALE ORGANIZATION PRECIPITATION AND CLOUD DROPLET CONCENTRATION TOGETHER WITH EXTERNAL METEOROLOGICAL CONTROLS AND ATTEMPTS TO DETERMINE HOW THESE COUPLINGS INFLUENCE CLOUD SYSTEM EVOLUTION ON A WIDE RANGE OF TIMESCALES. OBSERVATIONAL CONSTRAINTS ON PRECIPITATION AND PBL DEPTH AND THEIR EFFECTS ON CLOUD TRANSITIONS AND REGIONAL ALBEDO VARIABILITY ARE ESSENTIAL FOR IMPROVING CLIMATE MODEL PHYSICS AT THE INTERSECTION BETWEEN CLOUD MICROPHYSICS AND MACROPHYSICS.