ATMOSPHERIC WAVES PROPAGATING UPWARDS INTO THE EARTH'S UPPER ATMOSPHERE CAN SIGNIFICANTLY IMPACT THE STRUCTURE AND DYNAMICS OF THE THERMOSPHERE-IONOSPHERE (T-I) SYSTEM. THE WAVES CAN CAUSE MIXING IN THE LOWER THERMOSPHERE AFFECTING THE VERTICAL DISTRIBUTION OF TEMPERATURE SPECIES COMPOSITION AND NEUTRAL WINDS. TRADITIONALLY EDDY DIFFUSION FROM BREAKING GRAVITY WAVES HAS BEEN THE MAIN MECHANISM FOR MIXING IN THE LOWER THERMOSPHERE. THIS BASIC CONCEPT WAS CHALLENGED RECENTLY WITH THE SUGGESTION THAT A SIGNIFICANT FRACTION OF THE MIXING EXTENDS DEEPER INTO THE LOWER THERMOSPHERE AND COMES FROM DISSIPATION OF A BROAD SPECTRUM OF LOWER ATMOSPHERIC WAVES. IN ADDITION THERE IS INDICATION THAT PREVIOUSLY UN-MODELED SEMI-ANNUAL VARIATION IN NEUTRAL DENSITY IS CAPTURED IN SIMULATIONS USING PHYSICS-BASED COUPLED MODELS OF THE THERMOSPHERE AND IONOSPHERE DRIVEN BY THE MORE REALISTIC LOWER BOUNDARY CONDITIONS PROVIDED BY THE TERRESTRIAL WEATHER FORECAST MODELS. IN THIS PROPOSAL THE WHOLE ATMOSPHERE MODEL (WAM) AND THE PHYSICS-BASED COUPLED THERMOSPHERE IONOSPHERE PLASMASPHERE ELECTRODYNAMICS (CTIPE) MODELS WILL BE USED TO ELUCIDATE THE BALANCE BETWEEN THE RANGE OF PHYSICAL PROCESSES INDUCED BY THE TIDAL AND MODEL-RESOLVED GRAVITY WAVE SPECTRUM PROPAGATING FROM THE LOWER ATMOSPHERE AND TO QUANTIFY THEIR IMPACT ON THE T-I SYSTEM. THE OVERARCHING GOAL OF THIS PROPOSAL IS TO INVESTIGATE UNDERSTAND AND QUANTIFY THE RELATIVE CONTRIBUTION OF MIGRATING NON-MIGRATING TIDES AND RESOLVED GRAVITY WAVE DISSIPATION ON MIXING THROUGH THE LOWER THERMOSPHERE AND THE SUBSEQUENT IMPACT ON NEUTRAL TEMPERATURE COMPOSITION DENSITY WINDS AND PLASMA DENSITY. THIS PROPOSAL WILL ADDRESS THE FOLLOWING SCIENCE QUESTIONS: (1) WHAT IS THE RELATIVE CONTRIBUTION OF TURBULENCE TIDES GRAVITY WAVES AND GLOBAL CIRCULATION TO THE MIXING IN THE LOWER THERMOSPHERE? (2) HOW DO THE MIXING SOURCES IN THE LOWER THERMOSPHERE AFFECT THE NEUTRAL TEMPERATURE DENSITY WINDS AND COMPOSITION AND PLASMA DENSITY IN THE UPPER ATMOSPHERE? (3) WHAT IS THE DAY-TO-DAY VARIABILITY OF TIDAL AMPLITUDE AND PHASE AND WHAT IS ITS IMPACT ON THE THERMOSPHERE AND IONOSPHERE? THIS PROPOSAL S GOAL WILL BE ACHIEVED USING NUMERICAL SIMULATIONS AND A WIDE VARIETY OF OBSERVATIONS. YEARLONG WAM MODEL SIMULATIONS WILL BE PERFORMED AND A TIDAL ANALYSIS WILL BE USED TO EXTRACT MIGRATING AND NON-MIGRATING DIURNAL SEMIDIURNAL TERDIURNAL QUADIURNAL TIDES WITH ZONAL WAVE NUMBER RANGING FROM 1 TO 4. THE WAM FIELDS AND THE DOMINANT TIDAL MODES WILL BE INDIVIDUALLY IMPOSED ON THE CTIPE S LOWER BOUNDARY AND THEIR MIXING EFFECTS ON THE THERMOSPHERE AND IONOSPHERE AT VARIOUS HEIGHTS SEASONS LATITUDES AND LONGITUDES WILL BE QUANTIFIED. THIS PROCEDURE WILL BE PERFORMED FOR YEARLONG SIMULATIONS REPRESENTING SOLAR MINIMUM MEDIUM AND MAXIMUM CONDITIONS. CTIPE RESULTS WILL BE COMPARED TO A WIDE RANGE OF OBSERVATIONS IN THE THERMOSPHERE AND IONOSPHERE INCLUDING NASA S TIMED GUVI O/N2 RATIOS NEUTRAL DENSITY FROM NASA S GRACE SATELLITES NEUTRAL WINDS AND DENSITIES FROM GOCE AND CHAMP SATELLITES AND IONOSONDE NMF2 AND HMF2 MEASUREMENTS FROM LOWELL DIDBASE AND SPIDR. OBSERVATIONS FROM COSMIC-2 NASA S GOLD AND ICON MISSIONS WILL BE USED BASED UPON AVAILABILITY. THE MODEL/OBSERVATIONS COMPARISONS WILL DETERMINE THE EXTENT TO WHICH THE PHYSICAL PROCESSES DRIVING THE T-I SYSTEM ARE CURRENTLY UNDERSTOOD. THIS PROPOSAL ADDRESSES THE FOLLOWING HIGH LEVEL SCIENCE GOALS FROM THE 2013 HELIOPHYSICS DECADAL SURVEY: DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS . THIS INVESTIGATION ALSO MEETS THE HELIOPHYSICS SR PROGRAM HIGH PRIORITY GOALS OF USING DATA FROM CURRENT OR HISTORICAL NASA SPACECRAFT AND THEORY NUMERICAL SIMULATION AND MODELING TO ADDRESS THE SCIENCE GOALS.