IT IS WELL-KNOWN THAT DYNAMICAL VARIABILITY PLAYS AN IMPORTANT ROLE IN THE YEAR-TO-YEAR VARIATIONS IN STRATOSPHERIC TRACE GASES. MODEL SIMULATIONS USING CONSTANT EMISSIONS HAVE FURTHER REPEATEDLY DEMONSTRATED THAT THIS DYNAMICAL VARIABILITY CAN RESULT IN UNFORCED TRENDS IN TRACE GASES OVER DECADAL TIMESCALES THAT COMPLICATE THE DETECTION OF ANTHROPOGENICALLY-DRIVEN TRENDS. YET WE CURRENTLY LACK A MECHANISTIC UNDERSTANDING OF THE PROCESSES THAT DRIVE THIS DECADAL-SCALE VARIABILITY AND A QUANTIFICATION OF ITS IMPACT ON TRACE GAS TREND DETECTION AND ATTRIBUTION. THIS PROPOSAL BUILDS ON A STRONG FOUNDATION OF PREVIOUS WORK THAT HAS USED AURA MICROWAVE LIMB SOUNDER (MLS) MEASUREMENTS AND THE WHOLE ATMOSPHERE COMMUNITY CLIMATE MODEL (WACCM) TO ESTABLISH A CRITICAL ROLE FOR THE PERIODICITY AND SEASONAL TIMING OF THE QBO AS KEY DRIVERS OF DECADAL-SCALE VARIATIONS OF STRATOSPHERIC CIRCULATION AND TRACERS. THE PROPOSED WORK EXPANDS THIS ANALYSIS FROM A HEMISPHERIC TO A GLOBAL PERSPECTIVE CONSIDERS THE ROLE OF ENSO IN MODIFYING AND INTERACTING WITH THE QBO OVER DECADAL TIMESCALES AND DEVELOPS A TREND MODEL FOR LONG-LIVED STRATOSPHERIC TRACERS THAT INCORPORATES PHYSICALLY-BASED INDICES DESCRIBING THE LOW-FREQUENCY VARIABILITY ASSOCIATED WITH SEASONAL CYCLE QBO ENSO INTERACTIONS. THE PROPOSAL TEAM COMBINES ESTABLISHED EXPERTISE IN STRATOSPHERIC TRANSPORT AND CHEMISTRY ANALYSIS OF SATELLITE MEASUREMENTS GLOBAL MODELING AND SPATIOTEMPORAL STATISTICS TO TACKLE THESE CHALLENGING ISSUES. WE ALSO BRING A POWERFUL NEW TOOL TO BEAR IN THE FORM OF A NEW WACCM VERSION WITH A REALISTIC INTERNALLY GENERATED QBO WHOSE PARAMETERIZATION IS DEPENDENT ON CONVECTIVE ACTIVITY AND THUS SENSITIVE TO CHANGES IN SEA SURFACE TEMPERATURES. THE OUTCOMES OF OUR WORK ARE EXPECTED TO ADVANCE OUR UNDERSTANDING OF THE APPARENT INCONSISTENCY OF STRATOSPHERIC HCL TRENDS WITH KNOWN DECREASES IN SOURCE GAS EMISSIONS THE APPARENT DECLINE IN LOWER STRATOSPHERIC OZONE OVER THE PAST ~20 YEARS THE OCCURRENCE OF RAPID DECREASES IN COLD POINT TEMPERATURE AND LOWER STRATOSPHERIC WATER VAPOR AND THE CAUSE OF EXTREMELY LOW OZONE IN THE LOWER STRATOSPHERE IN 2011.