THE EARTH S IONOSPHERE VARIES DRAMATICALLY FROM ONE DAY TO THE NEXT EVEN DURING SOLAR- AND- GEO- MAGNETIC QUIET TIMES. UNDERSTANDING THE SOURCE OF THIS VARIABILITY IS AN IMPORTANT SCIENCE GOAL CALLED-OUT IN HELIOPHYSICS DECADAL SURVEY. PREVIOUS CASE STUDIES HAVE SHOWN THAT A SIGNIFICANT SOURCE OF THE DAY-TO-DAY VARIATIONS IN THE EQUATORIAL IONOSPHERE ORIGINATES FROM ATMOSPHERIC PLANETARY WAVES OF THE SAME PERIODS. HOWEVER PLANETARY WAVES DO NOT OCCUR ALL THE TIME AND SUCH CORRESPONDENCES BETWEEN PLANETARY WAVES IN THE ATMOSPHERE AND THEIR APPARENT SIGNATURES IN THE IONOSPHERE ARE OBSERVED ONLY DURING A FRACTION OF TIME. EXACTLY HOW OFTEN THESE CORRESPONDENCES OCCUR HOW IMPORTANT AND HOW WIDESPREAD THE IONOSPHERIC IMPACTS OF ATMOSPHERIC PLANETARY WAVES ARE HAVE NEVER BEEN SYSTEMATICALLY INVESTIGATED ACROSS A BROAD RANGE OF WAVE PERIODS. HERE WE PROPOSE A COMPREHENSIVE ANALYSIS OF 15+ YEARS OF CONCURRENT OBSERVATIONS OF THE ATMOSPHERE AND THE IONOSPHERE FROM NASA TIMED/SABER AND IGS GROUND-BASED GPS IN COMBINATION WITH THE ACE SOLAR AND MAGNETOSPHERIC MEASUREMENTS. WE WILL BUILD UPON THE APPROACH WE HAVE SUCCESSFULLY DEVELOPED FOR THE 3-DAY KELVIN WAVE [LIU ET AL. 2015] AND EXTEND OUR ANALYSIS TO INCLUDE ALL SHORT PERIOD (<10 DAYS) ROSSBY WAVES AT LOW-TO-MID LATITUDES. WE WILL IDENTIFY THE OCCURRENCES AND CHARACTERISTICS OF EACH WAVE FOR MANY CASES AND COMPARE THESE TO THEIR SIGNATURES IN THE IONOSPHERE. THIS STUDY WILL 1) QUANTIFY THE IMPORTANCE OF ATMOSPHERIC PLANETARY WAVES ON THE DAY-TO-DAY VARIATIONS OF THE IONOSPHERE; 2) IDENTIFY WHICH WAVES (AND WAVE PARAMETERS) THAT ARE THE MOST IMPORTANT IN CREATING IONOSPHERIC VARIATIONS; 3) DETERMINE THE SEASONAL AND SOLAR CYCLE CONDITIONS THAT FAVOR THE WAVES TO IMPACT THE IONOSPHERE. TOWARDS OBJECTIVE 1: WE WILL CALCULATE FOR EACH WAVE (2-DAY 5-DAY WAVE ETC.) THE TOTAL NUMBER OF CASES THAT HAVE CORRESPONDING SIGNATURES IN THE IONOSPHERE. THE SABER ATMOSPHERIC TEMPERATURE GPS IONOSPHERIC TEC AND ACE SOLAR WIND DATA ARE ALL AVAILABLE THROUGHOUT 2002-2016. BY ANALYZING THESE DATA WE WILL BE ABLE TO IDENTIFY MANY WAVE CASES AND SIMULTANEOUSLY THEIR IONOSPHERIC RESPONSES. THIS WILL ALLOW US TO OBTAIN SUFFICIENT SAMPLES TO QUANTIFY THE IMPORTANCE AND FREQUENCY OF EACH WAVE ON THE VARIATION OF THE IONOSPHERE. TOWARDS OBJECTIVE 2: USING THE SABER OBSERVATIONS (COMPLEMENTED WITH MLS AND GROUND-BASED DATA) WE CAN UNAMBIGUOUSLY IDENTIFY THE OCCURRENCE AND CHARACTERISTIC (PERIOD AMPLITUDE ZONAL WAVENUMBER VERTICAL WAVELENGTH PROPAGATION DIRECTION ETC.) OF EACH INDIVIDUAL WAVE CASE. THIS WILL ALLOW US TO DETERMINE IF THERE IS ANY CLEAR TREND BETWEEN THE WAVE PARAMETER AND THE ABILITY OF THAT WAVE TO IMPACT THE IONOSPHERE. TOWARDS OBJECTIVE 3: WE WILL INVESTIGATE IF THE IMPACT OF PLANETARY WAVES ON THE IONOSPHERE DEPENDS ON SEASON OR SOLAR CYCLE. USING THE DATA FROM 2002-2016 WE WILL BE ABLE TO ASSESS IF THE MOST INFLUENTIAL WAVES REMAIN THE SAME DURING DIFFERENT SEASONS AND FROM SOLAR MINIMUM TO MAXIMUM. RELEVANCE TO NASA TIMED MISSION AND HELIOPHYSICS DECADAL SURVEY THIS PROPOSED STUDY WILL IDENTIFY WHICH ACTUAL WAVES IN THE ATMOSPHERE ARE DEMONSTRABLY MOST INFLUENTIAL IN CREATING DAY-TO-DAY VARIATIONS IN THE IONOSPHERE (AND WHICH ARE NOT). THIS ADDRESSES THE PRIMARY GOAL OF THE TIMED/SABER EXPERIMENT TO ADVANCE OUR UNDERSTANDING OF THE FUNDAMENTAL PROCESSES IN THE MESOSPHERE AND LOWER THERMOSPHERE . THE STUDY ADDRESSES THE IMPORTANCE OF LOWER ATMOSPHERIC FORCING ON THE IONOSPHERIC VARIABILITY WHICH DIRECTLY ADDRESSES KEY SCIENCE GOAL 2 OF THE HELIOPHYSICS DECADAL SURVEY: DETERMINE THE DYNAMICS AND COUPLING OF EARTH S IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO TERRESTRIAL INPUTS.