ACCELERATED DECLINE OF ARCTIC SEA ICE HAS INCREASED THE AREA OF OPEN WATER AND THE MARGINAL ICE ZONE (MIZ) THE TRANSITION REGION FROM OPEN WATER TO PACK ICE. THIS ALLOWS GREATER ACCESS TO THE ARCTIC REGION THAN EVER BEFORE WHICH PRESENTS CHALLENGES AND OPPORTUNITIES FOR ACTIVITIES SUCH AS FISHERIES TRANSPORTATION AND RESOURCE EXPLORATION. TO ASSIST IN THE MANAGEMENT OF INCREASING ECONOMIC AND TRANSPORTATION ACTIVITIES IT IS IMPORTANT TO ENHANCE OUR ABILITY TO PREDICT SEA ICE FOR VARIOUS ARCTIC REGIONS PARTICULARLY THE MIZ. BECAUSE THE MIZ CONSISTS OF FLOES OF VARYING THICKNESSES AND SIZES THE STATE OF SEA ICE IN THE MIZ IS BEST DESCRIBED BY AN ICE THICKNESS DISTRIBUTION (ITD) AND A FLOE SIZE DISTRIBUTION (FSD).WE PROPOSE TO DEVELOP A NEW ENSEMBLE FORECAST SYSTEM BASED ON THE PAN-ARCTIC ICE-OCEAN MODELING AND ASSIMILATION SYSTEM(PIOMAS) THAT IS CAPABLE OF PREDICTING BOTH ITD AND FSD IN THE MIZ (INCLUDING ICE EDGE LOCATIONS) ON DAILY TO SEASONAL TIME SCALES. A CRITICALLY IMPORTANT COMPONENT OF THE FORECAST SYSTEM IS ITS INITIALIZATION USING ALL AVAILABLE AND RELEVANT SATELLITE AND AIRBORNE OBSERVATIONS INCLUDING SEA ICE CONCENTRATION THICKNESS AND FLOE SIZE AND SEA SURFACE TEMPERATURE. THE PROPOSED STUDY WILL ENHANCE OUR UNDERSTANDING OF VARIABILITY AND PREDICTABILITY OF MIZ PROCESSES AND WILL DEVELOP AND STRENGTHEN OUR ABILITY TO MAKE RELIABLE FORECASTS AS WELL AS EFFECTIVE REPRESENTATIONS OF THE FORECAST UNCERTAINTIES THROUGH IMPROVED MODEL PHYSICS AND USE OF SATELLITE DATA FOR MODEL INITIALIZATION. PARTICULAR ATTENTION WILL BE PLACED ON ASSIMILATING ICEBRIDGE AND CRYOSAT-2 ICE THICKNESS OBSERVATIONS TO IMPROVE THE REPRESENTATION OF INITIAL CONDITIONS AND PREDICTIONS. ASSIMILATING THESE OBSERVATIONS MAY GUIDE UTILIZATION OF ICE THICKNESS DATA FROM THE ANTICIPATED ICESAT-2 TO BE LAUNCHED IN 2016.THE RESEARCH HAS SIX PRIMARY OBJECTIVES: (1) CALIBRATE AND VALIDATE PIOMAS AND IMPROVE MODEL PHYSICS BASED ON FSD; CONDUCT HINDCASTS THAT ASSIMILATE SATELLITE (AND AIRBORNE) ICE CONCENTRATION AND THICKNESS AND SST OVER 1979 PRESENT. (2) DEVELOP AN ENSEMBLE FORECAST SYSTEM TO PREDICT BOTH ITD AND FSD IN THE MIZ AND ICE EDGE LOCATIONS WITH LEAD TIMES FROM DAYS TO THREE SEASONS. (3) QUANTIFY THE HISTORICAL AND CONTEMPORARY EVOLUTION OF ITD AND FSD IN THE MIZ AND ICE PACK INTERIOR; IDENTIFY KEY LINKAGES AND INTERACTIONS AMONG THE ATMOSPHERE SEA ICE AND OCEAN TO UNDERSTAND MECHANISMS AFFECTING THE VARIABILITY AND PREDICTABILITY OF ITD AND FSD. (4) MAINTAIN AND EXPAND THE UNIFIED SEA ICE THICKNESS CLIMATE DATA RECORD TO EASE ASSIMILATION OF SATELLITE AND ICEBRIDGE ICE THICKNESS DATA TO IMPROVE PIOMAS INITIAL CONDITIONS AND FORECAST ACCURACY. (5) ASSESS THE SYSTEMS PREDICTABILITY THROUGH CAREFUL FORECAST SKILL EVALUATION AND UNCERTAINTY ANALYSIS AND IDENTIFY AREAS FOR FURTHER IMPROVEMENT. (6) PARTICIPATE IN THE YEAR OF POLAR PREDICTION (YOPP) AND MAXIMIZE THE EXPOSURE AND UTILITY OF THE FORECASTS. AS WE CONDUCT HINDCASTS AND FORECASTS OF SEA ICE IN THE MIZ USING THE FORECAST SYSTEM WE WILL STRIVE TO ADDRESS THE FOLLOWING SCIENCE QUESTIONS: (A) WHAT ARE THE VARIABILITY AND TRENDS OF ITD AND FSD IN THE MIZ IN BOTH THE PACIFIC AND ATLANTIC SECTORS OF THE ARCTIC OCEAN OVER THE PERIOD 1979 PRESENT? (B) HOW DO ARCTIC CYCLONES AFFECT THE VARIABILITY AND PREDICTABILITY OF MIZ ITD AND FSD AND ICE EDGE LOCATIONS ON DAILY TO SEASONAL TIME SCALES? (C) WHAT IS THE RELATIVE IMPORTANCE OF PRECONDITIONING VERSUS ATMOSPHERIC FORCING IN THE VARIABILITY AND PREDICTABILITY OF THE MIZ? (D) WHAT ARE THE EFFECTS OF INITIALIZATION USING SATELLITE AND AIRBORNE ICE THICKNESS DATA IN THE FORECASTS OF MIZ ICE CONDITIONS AND ICE EDGE LOCATIONS? (E) WHAT IS THE IMPACT OF SUMMERTIME HEAT STORAGE IN THE UPPER OCEAN ON THE VARIABILITY AND PREDICTABILITY OF ITD AND FSD IN THE MIZ AS WELL AS IN THE INTERIOR OF THE ICE PACK?