MIXED-PHASE CLOUD PARAMETERIZATIONS WITHIN GLOBAL CLIMATE MODELSA MAIN CHALLENGE IN UNDERSTANDING HOW ANTHROPOGENIC BEHAVIOR INDUCES CLIMATE CHANGE IS MODEL DESCRIPTION OF CLOUD-AEROSOLINTERACTIONS AND CLOUD RADIATIVE FORCINGS. CLIMATE MODELING BEGINS WITH SPATIAL AND TEMPORAL DISCRETIZATION BUT CLOUD MICROPHYSICS OCCURS ON THE SUBGRID SCALE. TO INCORPORATE THESE PROCESSES PARAMETERIZATIONS ARE USED TO CALCULATE QUANTITIES THAT AFFECT LARGE-SCALE BEHAVIOR. THIS PROJECT WILL INVOLVE DEVELOPMENT OF A NOVEL PARAMETERIZATION FOR CLOUDS COMPOSED OF BOTH ICE AND WATER (MIXED-PHASE).CLOUDS AFFECT CLIMATE THROUGH THEIR RADIATIVE EFFECTS THEIR ROLE IN THE HYDROLOGICAL CYCLE AND THEIR CONVECTIVE MOVEMENT OF MASS AND ENERGY. THESE PHENOMENA ARE PARTICULARLY INFLUENTIAL IN THE ARCTIC WHERE EXTREME CONDITIONS AND FEEDBACKS MAGNIFY CLIMATE PERTURBATIONS. ACCELERATED TEMPERATURE INCREASES ICE SHEET RECESSION AND PERMAFROST MELT ALL ATTEST TO THIS ARCTIC SENSITIVITY AND MAKE ACCURATE REPRESENTATION OF MIXED-PHASE CLOUDS ESPECIALLY IMPORTANT.WE PROPOSE TO IMPROVE MIXED-PHASE CLOUD PARAMETERIZATIONS WITHIN THE ATMOSPHERIC GLOBAL CLIMATE MODEL OF NASAS GODDARD EARTH OBSERVING SYSTEM MODEL VERSION 5 (GEOS-5). OUR OBJECTIVE WILL BE TO CALCULATE THE MOST IMPORTANT PARAMETERS ASSOCIATED WITH MIXED-PHASE CLOUDS CLOUD LIQUID AND ICE WATER PATH DROPLET AND CRYSTAL NUMBER CONCENTRATIONS AND EFFECTIVE CLOUD PARTICLE RADIUS WITH ACCURACY AND COMPUTATIONAL EFFICIENCY. WE WILL INCORPORATE BOTH GENERAL CLOUD PROCESSES AND THOSE UNIQUE TO MIXEDPHASEEVOLUTION IN FOUR AREAS OF DEVELOPMENT: MICROPHYSICS ATMOSPHERIC DYNAMICS CLOUD RADIATIVE EFFECTS AND SURFACE INTERACTIONS.THE FIRST STEP IS SIMULTANEOUS IMPLEMENTATION OF CLOUD WATER AND ICE SOURCE AND SINK EQUATIONS AND INTERPHASE MASS TRANSFER EQUATIONS. THESE INCLUDE AEROSOL ACTIVATION TO CLOUD CONDENSATION NUCLEI (CCN) AND ICE NUCLEI (IN) CONDENSATION EVAPORATION ACCRETION AUTOCONVERSION AND HETEROGENEOUS (WITH A NUCLEATION SITE) AND HOMOGENEOUS (WITHOUT) FREEZING. CCN AND IN INPUT WITH VARYING CHEMICAL COMPOSITIONS AND SIZE DISTRIBUTIONS WILL BE TESTED. WE WILL INCLUDE FOUR MECHANISMS OF HETEROGENEOUS FREEZING ICE DEPOSITION CONDENSATION FREEZING CONTACT FREEZING AND IMMERSION FREEZING WITH DIFFERENT WEIGHTINGS IN DIFFERENT TEMPERATURE RANGES. AFTER THIS FUNDAMENTAL DEVELOPMENT CLOUD DYNAMICS (I.E. DOWNDRAFTS UPDRAFTS AND TURBULENCE) WILL BE INTEGRATED TO DETERMINE THE LAYERED STRUCTURE OF MIXED-PHASE CLOUDS. THE BUOYANT GENERATION OF TURBULENCE AND THE RELATIONSHIP BETWEEN AEROSOL LOADING AND CLOUD EMISSIVITY FALL UNDER CLOUD RADIATIVE EFFECTS. FINALLY THE MASS LOSS TO SURFACE BY HYDROMETEOR PRECIPITATION AND THE EFFECT OF SURFACE TYPE (I.E. OCEAN LAND OR ICE) ON FORMATION MUST BE INCLUDED. GIVEN THE COUPLED AND NONLINEAR NATURE OF THESE FOUR AREAS OF DEVELOPMENT ALL MUST BE PARAMETERIZED AS ACCURATELY AS POSSIBLE.ADDITIONALLY OUR PROJECT WILL EXPLORE SEVERAL SHORTCOMINGS AND SENSITIVITIES OF THE GEOS-5S MICROPHYSICS OF CLOUDS WITH RELAXED ARAKAWA-SCHUBERT AND AEROSOL-CLOUD INTERACTION SCHEME (MCRAS-AC). WE WILL ADDRESS PRECIPITATION BIASES BY ADJUSTING AEROSOL INPUT AND CLOUD FRACTION ERRORS BY LOOKING AT THE DRY CONVECTION SCHEME AND POLAR DIAMOND DUST FORMATION. SENSITIVITY STUDIES WILL ALSO BE USED TO DETERMINE WHICH PARAMETERS OF THE ICE FORMATION PROCESSES MOST DETERMINE THE RESULTANT CLOUD FIELD. FOR EXAMPLE THEINCORPORATION OF DIFFERENT FREEZING MECHANISMS HAS A SIGNIFICANT IMPACT ON THE PREDICTED NUMBER OF NUCLEATED ICE CRYSTALS.ULTIMATELY WE WOULD LIKE TO PERTURB THE PARAMETERIZATION PHASE SPACE TO ESTABLISH SYSTEM ATTRACTORS. THE DETERMINATION OF PREFERRED STATES AND ASSOCIATED RADIATIVE DIFFERENCES WILL BE ESSENTIAL IN CORRECTING THE RADIATION BUDGET AND IN PREDICTING THE INTENSIFIED INFLUENCE OF CLIMATE CHANGE IN THE ARCTIC. MORE BROADLY IMPROVED CLIMATE MODELS WILL HELP US UNDERSTAND HOW OUR BEHAVIOR IMPACTS THE EARTH SYSTEM AND HOW WE MIGHT MITIG