NEARLY TWO DECADES OF HIGH-ACCURACY LOW-EARTH ORBIT MAGNETIC FIELD MEASUREMENTS HAVE MADE IT POSSIBLE TO BUILD GLOBAL DATA-BASED MODELS OF RAPID CORE FIELD VARIATIONS. SUCH MODELS CAN BE USED TO BETTER CONSTRAIN PHYSICS-BASED MODELS OF THE GEODYNAMO AND FURTHER OUR UNDERSTANDING OF DEEP EARTH DYNAMICS. HOWEVER IT IS STILL UNCLEAR WHAT IS THE SMALLEST DETECTABLE TIME SCALE OF THE GEOMAGNETIC SIGNAL COMING FROM THE CORE. ASSUMING THEY REACH THE EARTH'S SURFACE SUB-ANNUAL CORE FIELD VARIATIONS ARE SUPERIMPOSED ONTO EXTERNAL FIELD VARIATIONS OF SIMILAR TIME SCALES IN BOTH GROUND-BASED AND SATELLITE-BASED RECORDS. THEREFORE THE KEY TO MAKING PROGRESS IN THIS AREA IS TO FIND WAYS TO BETTER SEPARATE INTERNAL AND EXTERNAL FIELDS AT SUB-ANNUAL TIME SCALES. THE INTENDED PROPOSAL WILL AIM AT DEVELOPING A NEW DATA-BASED MODEL OF THE MAGNETOSPHERIC FIELD AT AND NEAR THE EARTH'S SURFACE FROM A COMBINATION OF SATELLITE (SWARM CHAMP OERSTED) AND GROUND OBSERVATORY DATA. IT WILL FOCUS ON CAPTURING THE TIME-VARYING LONGITUDINAL ASYMMETRY OF THE RING AND TAIL CURRENTS WHICH IS NOT CONSIDERED IN EXISTING MAGNETOSPHERIC FIELD MODELS. THIS ASYMMETRY IS LIKELY TO SIGNIFICANTLY OVERLAP WITH RAPID CORE FIELD VARIATIONS. THE OBTAINED MAGNETOSPHERIC FIELD MODEL WILL THEN BE USED AS A TOOL TO EXTRACT RAPID CORE FIELD VARIATIONS FROM BOTH SATELLITE AND OBSERVATORY RECORDS INCLUDING OBSERVATORY RECORDS BEFORE THE SATELLITE ERA. SUCH RECORDS WILL ALLOW US TO INVESTIGATE THE FOLLOWING SCIENCE QUESTIONS: WHAT IS THE SMALLEST DETECTABLE TIME SCALE OF CORE FIELD VARIATIONS AT AND NEAR THE EARTH'S SURFACE? WHAT ARE THE SPATIO-TEMPORAL CHARACTERISTICS OF RAPID CORE FIELD VARIATIONS? THE FIRST QUESTION HAS IMPLICATIONS FOR OUR UNDERSTANDING OF NOT ONLY CORE DYNAMICS BUT ALSO THE LOWER MANTLE CONDUCTIVITY. THE SECOND QUESTION WILL PROVIDE OBSERVATIONS AGAINST WHICH TO TEST PHYSICS-BASED MODELS OF THE VARIOUS CORE PROCESSES PRODUCING RAPID FIELD VARIATIONS SUCH AS MAGNETO-HYDRODYNAMICAL WAVES AND CORE FLOWS.