SCIENCE GOALS AND OBJECTIVES: THE MERIDIONAL FLOW PLAYS AN IMPORTANT ROLE IN THE UNDERSTANDING OF A BROAD RANGE OF SOLAR PHENOMENA. FOR EXAMPLE THE SPEED AND PROFILE OF THE MERIDIONAL FLOW DETERMINES THE DURATION OF THE SOLAR CYCLE IN FLUX-TRANSPORT DYNAMO MODELS ITS RISE AND FALL PATTERN THE POLAR FIELD STRENGTH AND THE TIMING OF ITS REVERSAL. THE STRENGTH OF THE POLAR FIELD OF THE PREVIOUS MINIMUM PLAYS AN IMPORTANT ROLE IN DETERMINING THE STRENGTH OF THE NEXT CYCLE. THEREFORE IT IS IMPORTANT TO KNOW THE EVOLUTION OF THE POLAR FIELD WHICH IS LARGELY GOVERNED BY THE TRANSPORT BY MERIDIONAL CIRCULATION. WE PROPOSE TO STUDY THE MERIDIONAL FLOW IN THE SOLAR CONVECTION ZONE FROM THE SURFACE TO THE NEAR-SURFACE SHEAR LAYER USING RING-DIAGRAM ANALYSIS AND IN THE LOWER CONVECTION ZONE USING TIME-DISTANCE ANALYSIS ANALYZING SDO/HMI DOPPLERGRAMS. WE WILL THEN ASSIMILATE THE MERIDIONAL FLOW AND THE SURFACE MAGNETIC FIELD FROM SDO/ HMI INTO FLUX-TRANSPORT DYNAMO MODELS AND DRIVE THE MODELS WITH THE FLOWS. TO COVER MORE THAN ONE SOLAR CYCLE WE WILL ANALYZE MDI DATA SETS. THE GOALS OF THE PROPOSED PROJECT ARE (I) TO DETERMINE THE INFLUENCE OF THE MERIDIONAL FLOW ON DYNAMO-GENERATED MAGNETIC FIELDS DURING DIFFERENT PHASES OF THE SOLAR CYCLE AND (II) TO USE THE RESULTS TO PREDICT THE POLAR FIELDS DURING THE UPCOMING CYCLE MINIMUM AND THE STRENGTH OF CYCLE 25. THIS IS TIMELY SINCE SDO/HMI OBSERVATIONS COVER SOLAR CYCLE 24 AND THE HIGH SPATIAL RESOLUTION OF HMI ALLOWS US TO MEASURE SUBSURFACE MERIDIONAL FLOWS AT HIGH LATITUDES TO ABOUT 75 DEGREE. BY ASSIMILATING MERIDIONAL FLOWS AND SURFACE MAGNETIC FIELDS FROM SDO/HMI INTO DYNAMO MODELS WE WILL BE ABLE TO DETERMINE HOW WELL FLOW MEASUREMENTS CAN CONSTRAIN THE DYNAMO. RELEVANCE: THIS PROPOSAL DIRECTLY ADDRESSES THE FIRST SCIENCE GOAL FROM THE HELIOPHYSICS DECADAL SURVEY: DETERMINE THE ORIGINS OF THE SUN S ACTIVITY AND PREDICT THE VARIATIONS IN THE SPACE ENVIRONMENT . THE WORK PROPOSED HERE WILL GREATLY ENHANCE THE SCIENTIFIC RETURN OF THE SDO/HMI MISSION. METHODOLOGY: WE PROPOSE TO DETERMINE THE MERIDIONAL FLOW FROM SDO/HMI DOPPLERGRAMS USING TWO DIFFERENT HELIOSEISMIC TECHNIQUES. TO DETERMINE THE MERIDIONAL FLOW FROM THE SURFACE TO A DEPTH OF ABOUT 40 MM ON TIME SCALES OF DAYS AND MONTHS WE WILL USE RINGDIAGRAM ANALYSIS WITH THREE TILE SIZES. TO DISCERN THE CONTRIBUTIONS FROM ACTIVE REGIONS WE WILL STUDY FLOWS FROM SMALL 5 DEGREE TILES. TO REACH DEPTHS OF ABOUT 40 MM AND STUDY THE INFLUENCE OF THE NEAR-SURFACE SHEAR LAYER WE WILL USE FLOWS FROM 30 DEGREE TILES. WE WILL CROSS-VALIDATE THESE RESULTS WITH THOSE FROM THE STANDARD 15 DEGREE TILES COVERING DEPTHS FROM THE SURFACE TO ABOUT 16 MM. TO DETERMINE THE MERIDIONAL FLOW IN THE LOWER HALF OF THE CONVECTION ZONE ON TIME SCALES OF TWO YEARS WE WILL USE A CUSTOMIZED TIMEDISTANCE ANALYSIS. THE KEY POINT IS TO PERFORM THE ANALYSIS IN SPHERICAL GEOMETRY WHICH ALLOWS US TO ISOLATE ACOUSTIC WAVES PROPAGATING TO DEEP LAYERS. THIS WILL ALLOW US TO CONSTRAIN THE RETURN FLOW NEAR THE BASE OF THE CONVECTION ZONE AND THE NUMBER OF CELLS WITH DEPTH. WE WILL USE AN ENSEMBLE KALMAN FILTER TO ASSIMILATE THE SUBSURFACE MERIDIONAL FLOW AND THE SURFACE MAGNETOGRAMS INTO THE DYNAMO MODEL AND OPERATE THE MODEL IN THE ANALYSES AND THE FORECAST MODE SO THAT WE CAN RESOLVE UNCERTAINTIES IN MODEL INGREDIENTS IN THE ANALYSES PHASE AND CORRECTLY HINDCAST AND FORECAST THE POLAR FIELDS AND PROPERTIES OF SOLAR CYCLES 24 AND 25 IN THE FORECAST PHASE. WE WILL CHECK THE CONSISTENCY BETWEEN THE MERIDIONAL FLOWS DETERMINED IN THE UPPER AND LOWER CONVECTION ZONE ON DIFFERENT TEMPORAL AND SPATIAL SCALES AS WELL AS WHETHER THE MODEL WORKS BEST WITH HIGH OR LOW MAGNETIC DIFFUSIVITY. WE WILL DETERMINE THE CONSEQUENCES OF THE MERIDIONAL FLOW AT HIGH LATITUDES FOR THE POLEWARD FLUX TRANSPORT AND POLAR FIELD FEATURES AND IN TURN FOR THE CYCLE 25 AMPLITUDE