SUMMARY: THIS PROJECT WILL STUDY THE OCCURRENCE PROPERTIES AND IMPACT OF MAGNETIC RECONNECTION AT THIN CURRENT SHEETS IN THE TURBULENT MAGNETOSHEATH DOWNSTREAM OF EARTH S BOW SHOCK AS CONTROLLED BY INTERPLANETARY CONDITIONS BOW SHOCK PARAMETERS AND LOCATION WITHIN THE MAGNETOSHEATH. SCIENCE GOALS AND OBJECTIVES: THERE IS GROWING EVIDENCE THAT TURBULENT MAGNETIZED PLASMAS PROMOTE MAGNETIC RECONNECTION THROUGH THE GENERATION OF THIN CURRENT SHEETS. SUCH RECONNECTION MAY PLAY AN IMPORTANT ROLE IN THE REDISTRIBUTION OF ENERGY. A HANDFUL OF CASE STUDIES HAVE REVEALED THIN CURRENT SHEETS IN EARTH S MAGNETOSHEATH THAT SHOW SIGNATURES OF RECONNECTION. WHAT IS THE ROLE OF RECONNECTION IN THE PROGRESSION FROM THE UPSTREAM SOLAR WIND THROUGH THE MAGNETOSHEATH TO THE PLASMA DELIVERED TO THE MAGNETOPAUSE? THE TURBULENCE AND CURRENT SHEETS WITHIN THE MAGNETOSHEATH ARE CONTROLLED BY UPSTREAM SOLAR WIND CONDITIONS AND BY THE PLASMA FLOW THROUGH THE EARTH S BOW SHOCK. BEHIND THE QUASI-PERPENDICULAR PORTIONS OF THE SHOCK THE PLASMA IS STRUCTURED WITH WAVES DRIVEN UNSTABLE BY ION-SCALE ANISOTROPIES. THE QUASI-PARALLEL SHOCK CREATES AN EXTENDED UPSTREAM FORESHOCK FILLED WITH LARGEAMPLITUDE LOW FREQUENCY WAVES THAT CONVECT AND ARE PROCESSED BY THE SHOCK INTO A HIGHLY TURBULENT HETEROGENOUS PLASMA. WE WILL ESTABLISH THE CONTROL BY UPSTREAM CONDITIONS AND SHOCK PROPERTIES ON THE OCCURRENCE PROPERTIES AND LOCATION OF RECONNECTING CURRENT SHEETS IN THE MAGNETOSHEATH. WE WILL ALSO ASSESS THE OVERALL IMPACT OF THAT RECONNECTION ON THE RELAXATION AND REDISTRIBUTION OF SOLAR WIND BULK FLOW ENERGY THAT IS INITIATED BUT NOT COMPLETED AT THE BOW SHOCK. SCIENCE QUESTIONS: 1. HOW DO THE OCCURRENCE AND PROPERTIES OF RECONNECTING MAGNETOSHEATH CURRENTS SHEETS DEPEND ON INTERPLANETARY AND BOW SHOCK CONDITIONS? 2. WHAT IS THE ROLE OF RECONNECTING CURRENT SHEETS IN THE TRANSITION FROM THE SOLAR WIND TO THE HOT NON-EQUILIBRIUM MAGNETOSHEATH PLASMA THAT IMPINGES ON THE MAGNETOSPHERE? MISSION DATA: WE WILL USE MMS DATA INCLUDING DC AND AC ELECTRIC AND MAGNETIC FIELDS (EDP FGM SCM) THERMAL PLASMA DATA (FPI) AND HPCA ION COMPOSITION DATA. MMS IS UNIQUELY CAPABLE OF BOTH THE 4-POINT SPATIAL AND RAPID TEMPORAL RESOLUTION TO STUDY THIN ION OR ELECTRON SCALE CURRENT SHEETS AND HAS CAPTURED HUNDREDS OF THEM IN BURST MODE IN THE MAGNETOSHEATH. THE PROJECT WILL DRAW SUPPORT FROM SOLAR WIND MONITORS (ACE WIND) AND FROM CLUSTER PLASMA AND FIELD DATA. DATA ANALYSIS AND METHODOLOGY: WE WILL PRIMARILY USE MMS BURST-MODE DATA AT AND DOWNSTREAM OF EARTH S BOW SHOCK TO BUILD A DATABASE OF HUNDREDS OF MAGNETOSHEATH CURRENT SHEETS. WE WILL CATALOG KEY PARAMETERS INCLUDING CURRENT DENSITY PARTICLE-FIELD ENERGY EXCHANGE COMPOSITION UPSTREAM AND BOW SHOCK CONDITIONS AND LOCATION WITHIN THE MAGNETOSHEATH. RECONNECTION ANALYSES WILL INCLUDE CORRLEATIONS REVEALING THE PRESENCE OF OUTFLOWING RECONNECTION JETS AND SYSTEMATIC PARAMETER VARIATIONS ACROSS THE SHEETS. STATISTICAL ANALYSES WILL BE COMPLEMENTED BY INDIVIDUAL CASE STUDIES SET IN CONTEXT THROUGH NUMERICAL SIMULATIONS. TO ADDRESS SCIENCE QUESTION#1 WE WILL COMPILE A SET OF MAGNETOSHEATH CURRENT SHEETS CLASSIFIED ACCORDING TO THEIR RECONNECTION SIGNATURES (IF ANY) INTERPLANETARY CONDITIONS AND SHOCK PROPERTIES. TO ADDRESS SCIENCE QUESTION#2 WE WILL COMBINE THE LOCATION INFORMATION FROM OUR DATABASE WITH CLUSTER CONJUNCTIONS AND WITH ESTIMATED FRACTIONAL POSITION WITHIN THE MAGNETOSHEATH. RELEVANCE TO THE HSR PROGRAM: WE WILL USE DATA USE DATA FROM CURRENT OPERATING SPACE MISSIONS (MMS CLUSTER). THIS PROPOSAL ADDRESSES TWO OF THE MAIN SCIENCE GOALS OF THE DECADAL SURVEY: SCIENCE GOAL #2 DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS #4 DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE.