NITRIC OXIDE (NO) IS AN IMPORTANT CONSTITUENT IN THE THERMOSPHERE AND MESOSPHERE. IN THE THERMOSPHERE NO ACTS AS A NATURAL THERMOSTAT THAT COOLS TO SPACE FOLLOWING HEATING FROM SOLAR STORMS MODULATING ATMOSPHERIC DENSITY AND THEREBY INFLUENCING SATELLITE DRAG. IN THE MESOSPHERE AND LOWER THERMOSPHERE (MLT) NO IS AN INDICATOR OF SOLAR FORCING BY ENERGETIC PARTICLE PRECIPITATION (EEP) AND SOFT X-RAYS AND CAN BE USED AS A TRACER OF GRAVITY WAVE FORCING AND DYNAMICS DRIVEN FROM BELOW THAT AFFECTS SPACE WEATHER. DESCENT OF NO DURING POLAR WINTER COUPLES THE MLT TO THE STRATOSPHERE AND CAN LEAD TO OZONE DESTRUCTION BY ENHANCING ODD-NITROGEN (NOX). SEVERAL DATA-MODEL COMPARISONS HAVE SHOWN SIGNIFICANT ERRORS IN SIMULATIONS OF NOX. HEPPA-II (FUNKE ET AL. 2017) COMPARED DATA FROM 7 INSTRUMENTS WITH 8 MODELS FOR BOREAL WINTER 2008/9 DURING WHICH STRONG DESCENT OF NOX WAS DRIVEN BY A STRATOSPHERIC SUDDEN WARMING (SSW) AND FOUND ALL MODELS FAILED TO GENERATE ENOUGH NOX OR GET THE CORRECT TIMING AND DESCENT RATE. RANDALL ET AL. (2015) COMPARED HALOE DATA FOR 2003/4 WITH A WHOLE ATMOSPHERE COMMUNITY CLIMATE MODEL (WACCM) SIMULATION FINDING IT UNDERESTIMATED EPP NOX AND HAD WEAK DESCENT. HENDRICKX ET AL. (IN REVIEW) EVALUATED SH NO USING SOFIE AND SD-WACCM FINDING TOO LITTLE NO DESCENT SUGGESTING MISSING NO PRODUCTION. ARSENOVIC ET AL. (2016) FIND IMPROVEMENTS IN NOY BETWEEN SOCOL3 AND MIPAS BY INCLUDING MEDIUM ENERGY (>30 KEV) ELECTRONS (MEE). OUR GOAL IS TO DETERMINE WHAT AFFECTS NOX IN THE MLT AND CAUSES THIS BIAS IN THE MODELS. WE PROPOSE A 3-PRONGED APPROACH USING NO DATA FROM THE SOLAR OCCULTATION FOR ICE EXPERIMENT (SOFIE; GORDLEY ET AL. 2009) ON THE AIM SATELLITE AND TEMPERATURE DATA FROM THE SABER INSTRUMENT ON THE TIMED SATELLITE ALONG WITH SIMULATIONS FROM WACCM AND THE DATA ASSIMILATION RESEARCH TESTBED (DART) TO REDUCE THIS DISCREPANCY AND QUANTIFY THE CRITICAL DRIVERS THROUGHOUT THE ATMOSPHERE NAMELY FROM DYNAMICS CHEMISTRY AND SOURCES. SOFIE OBSERVATIONS ARE TAKEN AT LATITUDES FROM 65-82S (SUNSET) AND 65-82N (SUNRISE) FOLLOWING THE LATITUDE OF THE DAY-NIGHT TERMINATOR FROM 2007 TO PRESENT. SOFIE OBSERVATIONS SHOW ENHANCED DESCENT OF NO FOR 2009 AS WELL AS FOR 2 OTHER SSW EVENTS IN 2012 AND 2013. BAILEY ET AL. (2014) USED SOFIE NO H2O AND CH4 TO INVESTIGATE THE DESCENT OF NO DURING THE 2013 SSW. OUR PLAN IS TO FIRST STUDY THE 3 NH SSW PERIODS THEN THE OTHER NH WINTERS FOLLOWED BY THE SH SEASONS. WE WILL USE WACCM+DART TO INVESTIGATE THE EFFECTS OF DYNAMICS ON NOX AND TO PROVIDE AN IMPROVED ATMOSPHERIC STATE FOR OTHER SENSITIVITY TESTS INCLUDING ADJUSTMENTS TO GRAVITY WAVES. PEDATELLA ET AL. (2014) SHOWED THAT ASSIMILATING SABER TEMPERATURES WITH WACCM+DART PROVIDES A BETTER SIMULATION OF THE 2009 SSW THAN SD-WACCM WHICH NUDGES TO MERRA REANALYSIS. MERANER ET AL. (2016) FOUND THAT CHANGES IN GRAVITY WAVES IMPROVE NOX FOR THE 2009 SSW; HOWEVER THESE CHANGES CAN ALSO AFFECT WINDS TEMPERATURES AND OTHER TRACER DISTRIBUTIONS. WE WILL ALSO INVESTIGATE THE IMPORTANCE OF CHEMISTRY AND PARTICLE/IRRADIANCE FORCING ON THE NOX DISTRIBUTION USING THE LATEST VERSION OF WACCM THAT HAS SEVERAL SIGNIFICANT IMPROVEMENTS INCLUDING: HIGHER HORIZONTAL RESOLUTION D-REGION CHEMISTRY MEE TAGGED NOX CHEMISTRY AND A BETTER EPP SPECIFICATION DERIVED FROM THE ASSIMILATIVE MAPPING OF IONOSPHERIC ELECTRODYNAMICS (AMIE). THIS PROPOSAL SUPPORTS THE GOAL OF THE HELIOPHYSICS RESEARCH PROGRAM TO DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS. SOFIE AND SABER ARE PART OF THE HELIOPHYSICS SYSTEM OBSERVATORY. THIS WORK SUPPORTS THE GOALS OF THE TIMED MISSION TO ACHIEVE A MAJOR IMPROVEMENT IN OUR UNDERSTANDING OF THE FUNDAMENTAL PROCESSES GOVERNING THE ENERGETICS CHEMISTRY DYNAMICS AND TRANSPORT [ ] FROM 60 KM TO 180 KM AND OF THE AIM EXTENDED MISSION TO BETTER UNDERSTAND DYNAMICAL COUPLING GRAVITY WAVES AND MESOSPHERIC STRUCTURE.