THE OCEAN AND ATMOSPHERE EXERT STRESSES ON SEA ICE THAT CREATE ELONGATED CRACKS OR OPENINGS (LEADS) WHERE THE OCEAN IS EXPOSED DIRECTLY TO THE ATMOSPHERE. LEADS COVER A SMALL FRACTION OF THE SURFACE BUT DOMINATE THE VERTICAL EXCHANGE OF ENERGY PARTICULARLY IN WINTER WHEN TURBULENT HEAT FLUXES OVER LEADS CAN BE ORDERS OF MAGNITUDE LARGER THAN OVER THICK ICE. THE WIDTH OF LEADS AND THEIR ORIENTATION RELATIVE TO ATMOSPHERIC FLOW MARKEDLY INFLUENCE ASSOCIATED VERTICAL FLUXES RELEVANT TO CLOUD FORMATION WITH RECENT STUDIES SUGGESTING THAT THESE FLUXES CAN INFLUENCE THE ATMOSPHERIC PROPERTIES TENS TO HUNDREDS OF KILOMETERS DOWNSTREAM. ARCTIC SEA ICE IS CHANGING RAPIDLY AND OBSERVATIONAL AND MODELING RESULTS SUGGEST AN INCREASING INFLUENCE OF LEAD-INDUCED FEEDBACKS ON THE CLIMATE SYSTEM. FOR INSTANCE POSITIVE FEEDBACKS CAN RESULT IF LEADS ACT TO INCREASE CLOUD COVER WHICH THEN WARMS THE SURFACE LEADING TO MORE OR PERSISTENT OPEN WATER. IF CONVECTIVE PLUMES CAUSE ENTRAINMENT OF DRIER FREE TROPOSPHERIC AIR THAT DECREASES CLOUD COVER SURFACE COOLING AND A NEGATIVE FEEDBACK WOULD RESULT. BECAUSE LEADS ARE A CRUCIALLY IMPORTANT DRIVER OF THE ARCTIC SURFACE ENERGY BUDGET THEIR INCREASING PROMINENCE MAKES THE NEED FOR QUANTIFYING AND UNDERSTANDING THEIR IMPACT ON THE ARCTIC CLIMATE SYSTEM ESPECIALLY PRESSING AT THIS TIME. THE PROPOSED PROJECT TARGETS THE NASA CRYOSPHERIC SCIENCE PROGRAM S FOCUS ON UNDERSTANDING SEA ICE PROCESSES AND OBSERVED CHANGES TO THE ARCTIC SURFACE ENERGY BUDGET INCLUDING SEA ICE-ATMOSPHERE FEEDBACKS. OUR OVERARCHING OBJECTIVE IS TO UNDERSTAND THROUGH JOINT OBSERVATIONAL AND MODELING ACTIVITIES THE RELATIONSHIPS BETWEEN LEAD AREA FRACTIONS AND CLOUD PROPERTIES AND THE ARCTIC SURFACE ENERGY BUDGET. THIS OBJECTIVE ENTAILS THE FOLLOWING SPECIFIC ACTIVITIES: USE REMOTE SENSING DATA INCLUDING SEA ICE LEAD PROPERTIES WE DERIVE FROM AMSR-E AMSR2 SAR (ERS ENVISAT RADARSAT) OPTICAL (AVHRR AND MODIS) ICEBRIDGE DMS AREAL PHOTOS AND SUBMARINE DATA TO QUANTIFY THE STATISTICAL PROPERTIES OF SEA ICE LEADS ON MULTIPLE TIME AND SPACE SCALES. QUANTIFY HOW LEADS MODULATE THE SURFACE ENERGY BUDGET OF THE ARCTIC SYSTEM THROUGH FORCED CHANGES TO THE EXTENSIVE CLOUD SYSTEMS THAT OVERLIE THE SEA ICE USING DATA FROM CLOUDSAT CALIPSO AND THE A-TRAIN SUPPLEMENTED BY DATA COLLECTED AT THE ATMOSPHERIC RADIATION MEASUREMENT (ARM) SITES IN THE ARCTIC. EXTEND OUR PRIOR MODELING RESEARCH USING A THREE-DIMENSIONAL NONHYDROSTATIC CLOUD-RESOLVING (LARGE-EDDY SIMULATION) MODEL TO UNDERSTAND HOW PLUMES AND CLOUDS RESPOND TO SURFACE LEAD ORIENTATION AND SIZE DISTRIBUTIONS UNDER A RANGE OF SYNOPTIC ATMOSPHERIC REGIMES AND QUANTIFY THE ASSOCIATED IMPACTS ON THE ARCTIC SURFACE ENERGY BUDGET THESE ACTIVITIES WILL BE STRONGLY COUPLED BY USING ADVANCED STATISTICAL METHODS TO RELATE THE LEAD WIDTH AND ORIENTATION DISTRIBUTIONS TO THE CLOUD PROPERTIES CONTROLLING FOR CONFOUNDING FACTORS AND THEN USING THE OBSERVED RELATIONSHIPS TO INFORM THE MODELING WORK. OBSERVED LEAD STATISTICS AND A RANGE OF ATMOSPHERIC REGIMES WILL BE USED AS BOUNDARY CONDITIONS TO SIMULATE THE RESPONSE PATTERN AND ASSOCIATIONS IDENTIFIED VIA REMOTE SENSING. THIS QUANTITATIVE KNOWLEDGE IS ESSENTIAL FOR EVALUATING AND REFINING FORMULATIONS PROPOSED FOR PARAMETERIZING FLUXES OVER SUBGRID-SCALE LEADS IN CLIMATE MODELS THUS SUPPORTING THE OVERALL NASA CRYOSPHERIC SCIENCES PROGRAM GOAL OF USING REMOTE SENSING PRODUCTS TO VALIDATE AND IMPROVE MODELS OF CHANGES IN SEA ICE COVER TO ELUCIDATE CONNECTIONS TO THE GLOBAL SYSTEM.