AN OUTSTANDING GAP PERSISTS IN OUR UNDERSTANDING OF THE SOLAR DYNAMO. EVEN THOUGH NUMEROUS POTENTIALLY VIABLE DESCRIPTIONS OF THIS PHYSICAL SYSTEM NOW EXIST NOT ONE HAS BEEN CONVINCINGLY TIED TO DYNAMICS AT WORK IN THE SUN AND FOR GOOD REASON. CONVECTION AN INDISPENSABLE COMPONENT OF THE DYNAMO OCCURS IN THE MIDST OF ROTATION BUT THE MAGNITUDE OF ROTATIONAL INFLUENCE ON SOLAR CONVECTION REMAINS LARGELY UNQUANTIFIED. WE ARE NEVERTHELESS WELL AWARE THAT ROTATIONAL INFLUENCE PROFOUNDLY IMPACTS KEY COMPONENTS OF THE DYNAMO SUCH AS DIFFERENTIAL ROTATION AND MERIDIONAL CIRCULATION. THE HELICITY OF CONVECTIVE FLOWS A SOURCE OF TURBULENT EMF ALSO DERIVES FROM THE STRENGTH OF ROTATIONAL INFLUENCE. MOREOVER IT NOW SEEMS THAT CYCLIC DYNAMO BEHAVIOR IS REALIZED ONLY IN REGIMES OF RELATIVELY STRONG ROTATIONAL CONSTRAINT. MEASUREMENTS PROVIDE LIMITED INSIGHT INTO THIS ISSUE. BOTH TIME-DISTANCE AND RING-ANALYSIS HELIOSEISMOLOGY SUGGEST THAT SOLAR CONVECTION IS ROTATIONALLY CONSTRAINED AT THE BASE OF THE NEAR-SURFACE SHEAR LAYER. HOWEVER THESE TECHNIQUES PROVIDE ONLY TENUOUS INFORMATION CONCERNING THE BULK OF THE CONVECTION ZONE. FURTHER PROGRESS IN IDENTIFYING THOSE DYNAMO MECHANISMS AT WORK IN THE SUN ULTIMATELY REQUIRES THAT WE LEVERAGE THEORY AND OBSERVATIONS TO ASSESS THE DEGREE OF ROTATIONAL CONSTRAINT FELT BY SOLAR CONVECTION. SCIENCE GOALS: ROTATIONAL CONSTRAINT IS CHARACTERIZED BY A NON-DIMENSIONAL NUMBER KNOWN AS THE ROSSBY NUMBER. THE ROSSBY NUMBER EXPRESSES THE RATIO OF THE ROTATION PERIOD TO A TYPICAL CONVECTIVE TIMESCALE AND MIGHT DIFFER BETWEEN DIFFERENT SPATIAL SCALES OF THE CONVECTIVE FLOW. THE OVERARCHING SCIENCE GOALS FOR THIS PROPOSAL ARE TO ANSWER THE QUESTIONS: WHAT IS THE CHARACTERISTIC ROSSBY NUMBER OF THE SOLAR CONVECTION ZONE AND HOW DOES IT VARY WITH DEPTH AND ACROSS HORIZONTAL SPATIAL SCALES OF THE CONVECTION? WHAT ARE THE DYNAMICAL CONSEQUENCES OF THE SUN S PARTICULAR ROSSBY NUMBER REGIME? IN PARTICULAR WHAT IS THE SPECTRUM OF CONVECTIVE MOTIONS ASSOCIATED WITH THIS ROSSBY NUMBER AND WHAT IS ITS IMPACT ON THE DYNAMO? METHODOLOGY: IN PURSUING THIS RESEARCH WE WILL ADOPT A THREE-PRONGED STRATEGY INVOLVING THEORY COMPUTATION AND OBSERVATION: 1. WE WILL DEVELOP THEORETICAL MODELS OF SOLAR CONVECTIVE VELOCITY POWER SPECTRA THAT INCORPORATE ROTATIONAL EFFECTS OVER A RANGE OF ROSSBY NUMBERS. 2. WE WILL CARRY OUT NUMERICAL SIMULATIONS OF ROTATING MAGNETIZED SOLAR CONVECTION IN SPHERICAL GEOMETRY USING THE RAYLEIGH CONVECTION CODE. WE WILL USE RESULTS FROM THESE NONLINEAR SIMULATIONS TO TEST OUR THEORETICAL DESCRIPTION OF CONVECTIVE VELOCITY SPECTRA AS FORMED UNDER A RANGE ROSSBY NUMBERS. 3. USING RING-ANALYSIS HELIOSEISMOLOGY WE WILL MEASURE THE POWER SPECTRA OF THE CONVECTIVE FLOW FIELD AT A RANGE OF DEPTHS THROUGHOUT THE UPPER 40 MM OF THE CONVECTION ZONE. WE WILL SEARCH FOR THE SIGNATURE OF ROTATIONAL INFLUENCE IN THESE SPECTRA USING OUR THEORETICAL AND NUMERICAL RESULTS TO INTERPRET THE DEGREE TO WHICH THESE FLOWS SENSE ROTATION. THIS WORK WILL USE THEORY AND NUMERICAL SIMULATION TO FACILITATE THE INTERPRETATION OF HELIOSEISMIC OBSERVATIONS THAT ARE NOW CHALLENGING OUR UNDERSTANDING OF SOLAR CONVECTION. OBTAINING A BETTER KNOWLEDGE OF THE STRUCTURE OF SOLAR CONVECTION IS ONE OF THE MOST PRESSING ENDEAVORS TO PROMOTE PROGRESS IN OUR UNDERSTANDING OF THE SOLAR DYNAMO AND THE ORIGINS OF THE SOLAR ACTIVITY CYCLE. THUS THIS WORK LIES AT THE HEART OF NASA'S HELIOPHYSICS PROGRAM. IN PARTICULAR IT ADDRESSES THE FIRST AND FOURTH CHALLENGES IDENTIFIED IN THE 2013 2022 DECADAL SURVEY IN SOLAR AND SPACE PHYSICS: DETERMINE THE ORIGINS OF THE SUN'S ACTIVITY AND PREDICT THE VARIATIONS OF THE SPACE ENVIRONMENT ' AND DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE. THESE QUESTIONS FRAME THE SCIENCE OBJECTIVES OF MANY NASA MISSIONS MOST NOTABLY THE SOLAR DYNAMICS OBSERVATORY (SDO).