SCIENCE OBJECTIVES OF THE PROPOSED INVESTIGATION THE RADIANT ENERGY IN THE FAR-INFRARED EXPERIMENT (REFIRE) DETERMINES THE STRENGTH OF THE ARCTIC FAR-INFRARED (FIR; 15 50 MICRONS) GREENHOUSE EFFECT (GHE) AND ITS IMPACT ON SURFACE ENERGY IMBALANCES ICE LOSS AND NORTHERN HEMISPHERE CLIMATE. REFIRE CONTRIBUTES TO NASA S CLIMATE VARIABILITY AND WATER&ENERGY FOCUS AREAS BY ADDRESSING: WHAT IS THE ROLE OF ATMOSPHERIC COMPOSITION AND CLOUDS IN THE CLIMATE SYSTEM? WHAT ARE THE EFFECTS OF CLOUDS AND SURFACE HYDROLOGIC PROCESSES ON EARTH S CLIMATE? HOW ARE GLOBAL PRECIPITATION EVAPORATION AND THE CYCLING OF WATER CHANGING? AND HOW CAN PREDICTIONS OF CLIMATE VARIABILITY AND CHANGE BE IMPROVED? THE ARCTIC REGULATES THE EARTH S CLIMATE BY RADIATING MOST OF THE EXCESS ENERGY ABSORBED AT LOWER LATITUDES TO SPACE. THE ENHANCED ARCTIC GHE THAT RESULTS FROM CHANGES IN WATER VAPOR THIN ICE CLOUDS AND SURFACE MELTING THEREFORE EXERTS A STRONG INFLUENCE ON THE GLOBAL CLIMATE BY REDUCING THE EFFICACY OF THIS THERMOSTAT. YET CURRENT OBSERVING SYSTEMS FAIL TO PROVIDE THE FUNDAMENTAL MEASUREMENTS REQUIRED TO DIAGNOSE THE IMPACTS OF ARCTIC FEEDBACKS ON ICE SHEET MELT RATES SEA ICE RETREAT SURFACE AIR TEMPERATURES AND MID-LATITUDE WEATHER SYSTEMS. INDEED OVER HALF OF THERMAL EMISSION FROM THE ARCTIC OCCURS AT WAVELENGTHS LONGER THAN 15 MICRONS THAT HAVE NEVER BEEN SYSTEMATICALLY MEASURED ACROSS THE ARCTIC. THE REFIRE INVESTIGATION ADDRESSES THIS CRITICAL GAP BY PROVIDING FULLY-CALIBRATED SPECTRAL RADIANCES FROM 5 50 MICRONS WITH A RADIOMETRIC ACCURACY OF 3% FROM A LIGHTWEIGHT LOW-POWER THERMAL INFRARED SPECTROMETER (TIRS) ABOARD TWO 3U CUBESATS. THESE SPECTRA IN COMBINATION WITH DERIVED WATER VAPOR AND THIN ICE CLOUD PRODUCTS ALLOW UNAMBIGUOUS ASSESSMENT OF THE INFLUENCE OF ALL KEY FACTORS THAT MODULATE THE ARCTIC GHE. GENERAL DESIGN OR ARCHITECTURE THE REFIRE MISSION GLOBALLY SAMPLES THE SPECTRAL OUTGOING LONGWAVE RADIATION (OLR) OVER ONE COMPLETE ANNUAL CYCLE WITH TWO 3U CUBESAT SPACECRAFT FLYING IN NEAR-POLAR ORBITS. EACH OF THE 3U CUBESATS WILL CARRY A MINIATURIZED IR SPECTROMETER THAT SAMPLES THE INFRARED SPECTRUM FROM 5-50 MICRONS AT A UNIFORM 0.8 MICRON RESOLUTION. EACH RADIOMETER HAS 16 CROSS-TRACK CHANNELS WITH A SURFACE RESOLUTION OF 10 KM. MISSION OBJECTIVES ARE ADDRESSED THROUGH: (A) A SUITE OF ALGORITHMS APPLIED TO EACH RADIOMETER INDIVIDUALLY AND (B) ANALYSIS OF SCENE CHANGES IN SPECTRAL OLR ON SHORT TIME-SCALES DERIVED FROM ORBIT INTERSECTIONS BETWEEN THE TWO CUBESATS. FOR THE LATTER ANY COMBINATION OF EQUATORIAL CROSSING TIMES IS SUITABLE TO THE MISSION OBJECTIVES BECAUSE THE HIGH FREQUENCY OF ORBITAL INTERSECTIONS AT POLAR LATITUDES ENABLES SCENE CHANGES TO BE QUANTIFIED OVER PERIODS RANGING FROM ONE TO SEVERAL HOURS. PERCEIVED SIGNIFICANCE BY QUANTIFYING THE SPECTRAL VARIATION OF EMITTED RADIATION ACROSS MID- AND FAR-INFRARED WAVELENGTHS THAT ACCOUNT FOR 90% OF THE TOTAL ARCTIC LONGWAVE EMISSION REFIRE FILLS A CRITICAL GAP IN GLOBAL OBSERVING SYSTEMS. THE INVESTIGATION HAS THE FOLLOWING OBJECTIVES: (1) SUBSTANTIALLY REDUCE UNCERTAINTY IN ARCTIC ENERGY BALANCE CLOSURE AND DETERMINE THE STRENGTH OF THE FIR GHE ON MONTHLY TO SEASONAL TIMESCALES; (2) DETERMINE THE RELATIVE IMPORTANCE OF ATMOSPHERIC WATER VAPOR CLOUD PROPERTIES AND SURFACE CHARACTERISTICS IN DEFINING THE FIR GHE ACROSS A COMPLETE FREEZE-MELT CYCLE; AND (3) ESTABLISH THE IMPORTANCE OF FIR FEEDBACKS IN ARCTIC AMPLIFICATION OF CLIMATE CHANGE.