PASSIVE MICROWAVE SENSORS PROVIDE A LONG HISTORY OF SEA ICE CONCENTRATION FROM SATELLITE DATA SUITABLE FOR TRACKING CLIMATE CHANGE AND VARIABILITY. SEA ICE EXTENT AND ARU HAVE LONG BEEN CONSIDERED KEY CLIMATE INDICATORS AND HAVE BEEN INCLUDED IN NUMEROUS ASSESSMENT AND CLIMATE INDICATOR REPORTS. HOWEVER THESE TWO PARAMETERS PROVIDE ONLY LIMITED INFORMATION ABOUT THE CHARACTER OF THE SEA ICE; IN ADDITION THEY HAVE LIMITED SKILL AS INDICATORS OF FUTURE SEA ICE CONDITIONS BOTH SEASONAL AND INTERANNUALLY. HERE WE PROPOSE A SUITE OFINTER-RELATED SEA ICE CLIMATE INDICATORS THAT GO BEYOND EXTENT AND AREA TO DESCRIBE THE SEASONAL EVOLUTION OF THE ARCTIC SEA ICE COVER FROM SPRING THROUGH AUTUMN. SPECIFICALLY WE PROPOSE TO DEVELOP THREE INDICATORS: (1) SEA ICE MELT ONSET/FREEZE-UP (2) SEA ICE RETREAT/ADVANCE AND (3) FETCH. AN HISTORICAL TIME SERIES OF THESE FIELDS WILL BE PRODUCED FOR EACH PARAMETER FROM THE START OF THE PASSIVE MICROWAVE RECORD IN 1979 WITH CONTINUING UPDATES. STATISTICS ON TRENDS AND VARIABILITY WILL BE CALCULATED AND VISUALIZATIONS AND METRICS WILL BE DEVELOPED TO EASILY CONVEY THE INFORMATION. THE INDICATORS WILL BE PRODUCED ARCTIC-WIDE BUT REGIONAL BREAKDOWNS WILL ALSO BE PERFORMED WITH A PARTICULAR FOCUS ON THE ALASKAN REGION. THESE THREE PARAMETERS WILL INFORM A VARIETY OF STAKEHOLDERS. FOR EXAMPLE THE TIMING OF MELT ONSET AND THE DATE OF SEA ICE RETREAT CAN PROVIDE USEFUL INFORMATION ON THE EVOLUTION OF THE ICE COVER THROUGH THE REST OF THE SUMMER AND THUS BE USEFUL TO EFFORTS TO IMPROVE SEASONAL SEA ICE FORECASTS. MELT ONSET IS ALSO AN INDICATOR FOR SUMMER MINIMUM EXTENT SINCE IT PLAYS A KEY ROLE IN THE AMOUNT OF SOLAR ENERGY ABSORPTION AND ALONG WITH FREEZE UP THE OVERALL ENERGY BALANCE OF THE ARCTIC CLIMATE SYSTEM. THE LENGTH OF THE OPEN WATER SEASON IS IMPORTANT FOR HUMAN ACTIVITIES AND FOR WILDLIFE. THE LONG TIME SERIES THAT WILL BE PRODUCED WILL INFORM FUTURE PLANNING OF MILITARY CIVILIAN AND COMMERCIAL INFRASTRUCTURE. FETCH THE OPEN WATER DISTANCE BETWEEN THE SHORE AND ICE COVER IS IMPORTANT FOR NAVIGATION AND PLAYS A KEY ROLE IN POTENTIAL COASTAL DAMAGE DUE TO WINDS AND WAVES. INTERACTIVE TOOLS AND VISUALIZATIONS WILL BE DEVELOPED TO DISPLAY AND HELP ANALYZE THE INFORMATION. OUR PROJECT WILL USE PASSIVE MICROWAVE BRIGHTNESS TEMPERATURES AND SEA ICE CONCENTRATION FIELDS DERIVED FROM THEM TO PRODUCE OUR NEW CLIMATE INDICATORS. WE WILL USE CONCENTRATION ALGORITHMS DEVELOPED AT NASA GODDARD. HOWEVER THERE ARE A VARIETY OF DIFFERENT ALGORITHMS AND THE RESULTING CONCENTRATION FIELDS DO NOT INCLUDE AN UNCERTAINTY ESTIMATE AND DO NOT TYPICALLY HAVE A QUANTIFIABLE BASIS TO DERIVE EXTENT UNCERTAINTY. THIS LEADS TO CONFUSION AND INCONSISTENCY IN THE ESTIMATES. THE NOAA/NSIDC SEA ICE CLIMATE DATA RECORD CREATED FROM THE NASA SATELLITE PRODUCTS PROVIDES THE MEANS TO PROVIDE A SINGLE AUTHORITATIVE SEA ICE CONCENTRATION ESTIMATE; ALSO ALL PROCESSING METHODS ARE FULLY DOCUMENTED REPRODUCIBLE AND PUBLICALLY AVAILABLE. THIS IS ESSENTIAL FOR PUBLIC CONFIDENCE IN THE INDICATORS. THUS IN THIS PROPOSAL WE PLAN TO USE THE NASA PRODUCTS AS DISTRIBUTED THROUGH THE CLIMATE DATA RECORD FRAMEWORK AS THE SOURCE OF SEA ICE CONCENTRATION FOR THE RETREAT/ADVANCE AND FETCH INDICATORS. MELT ONSET AND FREEZE-UP ARE CALCULATED DIRECTLY FROM BRIGHTNESS TEMPERATURES THE SAME SOURCE DATA USED FOR THE SEA ICE CONCENTRATIONS WHICH PROVIDES CONSISTENCY ACROSS THE INDICATORS.