PERTURBATIONS IN IONOSPHERIC TOTAL ELECTRON CONTENT (DTEC) WITH TIMESCALES OF ~10S-1000S CAN BE DRIVEN FROM ABOVE BY PROCESSES IN THE MAGNETOSPHERE - INCLUDING MAGNETOSPHERIC ULTRA LOW FREQUENCY (ULF) WAVES - AND BELOW BY PROCESSES SUCH AS EARTHQUAKES THAT COUPLE TO ACOUSTIC-GRAVITY WAVES IN THE ATMOSPHERE. CHARACTERIZING THE SUBSET OF DTEC RELATED TO ULF WAVES IS OF HIGH PRIORITY AS SEVERAL STUDIES HAVE SHOWN THESE PERTURBATIONS IMPACT IONOSPHERIC SPACE WEATHER. FOR EXAMPLE CASE STUDIES HAVE SHOWN THAT ULF WAVES CAN PRODUCE EXTREME DTEC IN SOME CASES LEADING TO A MODULATION OF HEIGHT-INTEGRATED IONOSPHERIC CONDUCTANCES BY A FACTOR OF 7 TO 10. THESE EXTREME PERTURBATIONS CAN IN TURN AFFECT IONOSPHERE/THERMOSPHERE HEATING RATES COUPLING TO GEOMAGNETIC PERTURBATIONS THAT AFFECT GEOMAGNETICALLY INDUCED CURRENTS (GIC) AND SCINTILLATION THESE ARE ALL SPACE WEATHER HAZARDS. HOWEVER SINCE MOST WORK HAS FOCUSED ON SINGLE EVENT STUDIES WE HAVE LIMITED INFORMATION ON HOW OFTEN THESE EXTREME DTEC EVENTS OCCUR AND THEIR FAVORED LOCATIONS AND DRIVING CONDITIONS. IN THE ABSENCE OF A COMPREHENSIVE STATISTICAL STUDY IT IS CURRENTLY UNKNOWN WHETHER ULF WAVES ROUTINELY DRIVE DTEC OF SIGNIFICANCE FOR SPACE WEATHER. MOREOVER PAST WORK HAS DEMONSTRATED MULTIPLE MECHANISMS TO GENERATE DTEC HOWEVER DUE TO A LACK OF REALISTIC NUMERICAL SIMULATIONS THAT CAPTURE IONOSPHERE-THERMOSPHERE (I-T) COUPLING THERE IS LIMITED INFORMATION REGARDING (1) HOW MULTIPLE MECHANISMS MAY CONTRIBUTE SIMULTANEOUSLY TO THE DTEC AND (2) HOW IONOSPHERE THERMOSPHERE COUPLING AFFECTS THE TEC RESPONSE. THE PROPOSED STUDY WILL MAKE PROGRESS ON THESE CHALLENGES BY ADDRESSING THE OVER-ARCHING QUESTION "ARE SPACE-WEATHER SIGNIFICANT ULF TEC PERTURBATIONS ROUTINELY DRIVEN BY MAGNETOSPHERIC WAVES?" AND SUB-QUESTIONS "WHAT ARE THE DISTINGUISHING FEATURES OF TEC PERTURBATIONS DRIVEN BY MAGNETOSPHERIC ULF WAVES?" AND "WHAT ARE THE FAVORED MECHANISMS/CONDITIONS TO DRIVE TEC PERTURBATIONS OF SIGNIFICANCE FOR SPACE WEATHER?" WE WILL ADDRESS THESE QUESTIONS USING (1) A STATISTICAL STUDY OF MULTI-POINT TEC GROUND MAGNETOMETER MEASUREMENTS AND NASA SATELLITE OBSERVATIONS COMBINED WITH VOLCANO/EARTHQUAKE LISTS (2) NUMERICAL EXPERIMENTS USING GLOBAL IONOSPHERE THERMOSPHERE MODEL (GITM) DRIVEN BY ULF ELECTRIC FIELD PERTURBATIONS WITH DIFFERENT TEMPORAL AND SPATIAL SCALES (CONSTRAINED BY PREVIOUS OBSERVATIONS) AND (3) DATA-MODEL COMPARISONS DURING DETAILED CASE STUDIES WITH CONSTRAINTS ON THE SOURCE OF MAGNETOSPHERIC ULF WAVE ACTIVITY IONOSPHERIC ELECTRIC FIELDS AND MULTI-POINT TEC OBSERVATIONS. THE PROPOSED WORK IS RELEVANT TO THE HSR PROGRAM BECAUSE A) IT INCLUDES NUMERICAL SIMULATION (GITM) (B) IT INCLUDES DATA ANALYSIS AND INTERPRETATION OF NASA-SPACECRAFT OBSERVATIONS AND (C) IT IS RELEVANT TO THE HELIOPHYSICS PROGRAM OVERARCHING GOAL TO "TO UNDERSTAND THE SUN AND ITS INTERACTIONS WITH THE EARTH AND THE SOLAR SYSTEM INCLUDING SPACE WEATHER" BECAUSE WE WILL MAKE PROGRESS IN UNDERSTANDING THE ROLE OF ULF WAVES IN DRIVING TEC PERTURBATIONS WITH LARGE AMPLITUDES WHICH AFFECT IONOSPHERIC CONDUCTIVITY AND CAUSE SPACE WEATHER IMPACTS (SEE ABOVE). THERE IS A HIGH POTENTIAL IMPACT FOR THIS PROJECT BECAUSE WE ARE ADDRESSING UNRESOLVED QUESTIONS WITH NEW TOOLS AND APPROACHES: (1) WE WILL PERFORM A STATISTICAL STUDY WITH SATELLITE CONJUNCTIONS WHEREAS MOST PAST WORK FOCUSED ON EVENT STUDIES/SMALL INTERVALS (2) WE WILL CONSIDER DRIVING FROM THE MAGNETOSPHERE AND THE SURFACE/LOWER ATMOSPHERE IN THE SAME INVESTIGATION (3) WE WILL USE 1-S AND 5-S TEC MEASUREMENTS INSTEAD OF MORE WIDELY AVAILABLE 30-S MEASUREMENTS THAT CANNOT ADEQUATELY SAMPLE SIGNIFICANT PARTS OF THE ULF RANGE. THIS INVESTIGATION IS ALSO TIMELY WITH ADVANCED I-T MODELING CAPABILITIES NOT AVAILABLE BEFORE THAT ARE CRUCIAL TO CAPTURE SPATIALLY LOCALIZED ULF WAVES AND SURFACE DISTURBANCES.