MULTIPOINT MEASUREMENTS IN THE INNER MAGNETOSPHERE CAN ALLOW THE SPATIAL AND TEMPORAL EVOLUTION OF VARIOUS PARTICLE POPULATIONS AND WAVE MODES TO BE DISENTANGLED. IN PARTICULAR SPATIAL SCALES OF WAVE ACTIVE REGIONS HAVE RECENTLY BEEN ESTIMATED FOR A RANGE OF WAVE MODES INCLUDING WHISTLER MODE CHORUS ELECTROMAGNETIC ION CYCLOTRON (EMIC) AND QUASI-PERIODIC WAVES. UNDERSTANDING THE DRIVERS CONTROLLING THE SPATIAL SCALES OF WAVE ACTIVITY IN THE INNER MAGNETOSPHERE IS CRITICAL FOR UNCOVERING THE UNDERLYING PHYSICS BEHIND THE WAVE GENERATION AS WELL AS FOR BETTER PREDICTION OF WHERE AND WHEN WAVES WILL BE PRESENT. RECENT STUDIES OF EMIC WAVES REVEAL A DEPENDENCE OF THE WAVE SPATIAL EXTENT ON MAGNETIC LOCAL TIME (MLT) WAVE FREQUENCY AND L SHELL. VARIOUS HYPOTHESES HAVE BEEN PROPOSED TO EXPLAIN SOME OF THESE PATTERNS INCLUDING DIFFERENT SOURCES (AND SPATIAL EXTENTS) OF ION ANISOTROPY ON THE DAY VERSUS NIGHT SIDE COMPOSITIONAL VARIATIONS THROUGHOUT THE INNER MAGNETOSPHERE OR COLD PLASMA DENSITY STRUCTURE. STUDIES OF ION DYNAMICS IN THE INNER MAGNETOSPHERE HAVE SHOWN RAPID EVOLUTION IN SPATIAL STRUCTURES AND BOUNDARIES AS WELL AS COMPOSITION BUT THE RELATIONSHIP BETWEEN THESE VARIATIONS AND CHARACTERISTIC EMIC WAVE SCALES HAS YET TO BE EXPLORED. THIS WORK PROPOSES TO USE MULTIPOINT MEASUREMENTS AND ANALYSIS TECHNIQUES TO DETERMINE THE SPATIAL AND TEMPORAL EXTENTS AND EVOLUTION OF PLASMA STRUCTURES IN THE INNER MAGNETOSPHERE TO BETTER UNDERSTAND THE DRIVERS OF MAGNETOSPHERIC WAVE CHARACTERISTIC SCALES. IN PARTICULAR WE FOCUS ON EMIC WAVES AND THE PLASMA PARAMETERS IMPORTANT FOR THEIR GROWTH NAMELY COLD PLASMA DENSITY AND WARM ION DENSITY ANISOTROPY AND COMPOSITION. STRUCTURES AND BOUNDARIES IN THE LOCAL PLASMA POPULATIONS CAN HAVE DIRECT IMPACT ON WHERE AND WHEN WAVE GROWTH CAN OCCUR. THE PROPOSED WORK WILL ADDRESS THE IMPORTANT QUESTION OF WHAT PHYSICAL PARAMETERS CONTROL EMIC WAVE CHARACTERISTICS AND HOW DO THESE VARY THROUGHOUT THE INNER MAGNETOSPHERE. UTILIZING DATA FROM THE VAN ALLEN PROBES AND THEMIS MISSIONS WE PROPOSE TO: 1. INVESTIGATE SPATIAL STRUCTURES OF H+ HE+ AND O+ POPULATIONS IN THE INNER MAGNETOSPHERE. THE MULTIPLE PROBES CAN REVEAL THE TEMPORAL EVOLUTION OF THESE STRUCTURES AND HOW PERSISTENT VARIOUS PLASMA BOUNDARIES AND GRADIENTS ARE. 2. ESTIMATE ION ANISOTROPY AND THE SPATIAL SCALES OF ANISOTROPIC REGIONS. VARIATIONS IN THESE SCALES ACROSS L SHELL AND MLT MAY SUGGEST DIFFERENT PHYSICAL MECHANISMS GENERATING THESE ANISOTROPIES. 3. CHARACTERIZE COLD PLASMA DENSITY STRUCTURE INCLUDING FINE SCALE STRUCTURE AND ITS VARIABILITY ACROSS L SHELL AND MLT. DR. LAUREN BLUM PI HAS WORKED ON NUMEROUS STUDIES RELATED TO EMIC WAVES - INCLUDING WAVE SPATIAL AND COHERENCE SCALE ESTIMATIONS AND INVESTIGATIONS OF THE FREE ENERGY SOURCES FOR WAVE GROWTH. DR. MICK DENTON CO I HAS STUDIED PLASMASPHERIC STRUCTURE AND REFILLING PROCESSES. RECENT WORK INCLUDES INVESTIGATIONS OF STORM-TIME ION DYNAMICS AND COMPOSITIONAL VARIATIONS IN EARTH S MAGNETOSPHERE. RELEVANCE TO NASA PROGRAMS: THIS PROPOSAL RELATES DIRECTLY TO TWO OF THE FOUR HELIOPHYSICS DECADAL SURVEY GOALS DETERMINING THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS AND DISCOVERING AND CHARACTERIZING FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE. THE GENERATION OF PLASMA WAVES IS A CRITICAL PROCESS THROUGHOUT THE HELIOSPHERE; THE PROPOSED WORK WILL HELP DETERMINE THE FACTORS CONTROLLING WHERE AND WHEN PLASMA WAVES DEVELOP IN THE INNER MAGNETOSPHERE AND WHAT THE UNDERLYING PHYSICAL PROCESSES CONTROLLING WAVE SPATIAL AND TEMPORAL SCALES ARE.