THE MAJORITY OF ATLANTIC BASIN TROPICAL CYCLONES INTERACT WITH AT LEAST ONE UPPER-TROPOSPHERIC TROUGH DURING THEIR LIFE SPAN AND FORECASTING TROPICAL CYCLONE INTENSITY CHANGE DURING A TROUGH INTERACTION REMAINS A SIGNIFICANT CHALLENGE. THIS CHALLENGE EXISTS BECAUSE TROPICAL CYCLONE TROUGH INTERACTIONS INVOLVE COMPETING PROCESSES THAT DETERMINE THE TROUGH S INFLUENCE ON TROPICAL CYCLONE STRUCTURE AND INTENSITY. THESE PROCESSES INCLUDE THE POSITIVE EFFECTS OF TROUGH-ENHANCED UPPER-LEVEL DIVERGENCE AND EDDY MOMENTUM FLUXES AND THE NEGATIVE EFFECTS OF TROUGH-INDUCED VERTICAL WIND SHEAR. ATTEMPTING TO UNTANGLE THESE COMPETING PROCESSES RECENT RESEARCH CONDUCTED BY THE INVESTIGATORS (PIS ) GROUP DEMONSTRATED THAT TROUGHS ARE A NEGATIVE INFLUENCE ON INTENSIFICATION. FURTHERMORE EDDY MOMENTUM FLUXES PREVIOUSLY SHOWN TO POSITIVELY AFFECT TROPICAL CYCLONE INTENSITY ARE A WEAK PREDICTOR OF INTENSITY CHANGE COMPARED TO VERTICAL WIND SHEAR. WE PROPOSE TO BUILD UPON THE RESULTS ABOVE USING THE WEALTH OF DATA COLLECTED DURING RECENT NASA FIELD CAMPAIGNS (CAMEX-3 THROUGH HS3) IN TROPICAL CYCLONES THAT EXPERIENCED TROUGH INTERACTIONS. FOCUSING ON THE EFFECTS OF VERTICAL WIND SHEAR WE SEEK TO CLARIFY THE MECHANISMS BY WHICH SHEAR INTERACTS WITH THE TROPICAL CYCLONE VORTEX IN TERMS OF VORTEX TILT THE EXCITATION OF CONVECTIVE ASYMMETRIES AND VENTILATION OF THE CORE WITH ENVIRONMENTAL AIR. SPECIFICALLY WE PROPOSE TO ADDRESS THE FOLLOWING TWO QUESTIONS: 1) IS THE INTENSITY CHANGE OF A TROPICAL CYCLONE EXPERIENCING A TROUGH INTERACTION DEPENDENT ON THE TILT AND CONVECTIVE RESPONSE OF THE VORTEX TO THE TROUGH-INDUCED VERTICAL WIND SHEAR? 2) IS THERE OBSERVATIONAL EVIDENCE TO SUPPORT RECENT THEORETICAL AND MODELING STUDIES ON VERTICAL WIND SHEAR INDUCED VENTILATION IN TROPICAL CYCLONES? TO ADDRESS THESE QUESTIONS THE PROPOSED RESEARCH WILL TAKE ADVANTAGE OF THE EXTENSIVE DC-8 ER-2 GH AND WB-57 PAYLOAD INSTRUMENTATION IDEALLY SUITED TO MEASURE THE THREE-DIMENSIONAL EVOLUTION OF TCS AND THE ENVIRONMENTS IN WHICH THEY ARE EMBEDDED. WE WILL MAKE CONSIDERABLE USE OF DROPSONDES TO DOCUMENT THE KINEMATIC AND THERMODYNAMIC STRUCTURE OF BOTH THE ENVIRONMENT AND THE TROPICAL CYCLONE NEAR CORE. APR-2 AND HIWRAP REFLECTIVITY AND VERTICAL VELOCITIES WILL BE USED TO DOCUMENT INNER CORE CONVECTIVE STRUCTURES AND THEIR EVOLUTION AS WELL AS TO QUANTIFY MESOSCALE UPDRAFTS AND DOWNDRAFTS ORGANIZED BY THE VERTICAL WIND SHEAR. FINALLY HAMSR AND S-HIS DATA ALONG WITH DROPSONDES WILL BE USED TO DOCUMENT THE THERMODYNAMIC STATE OF THE ATMOSPHERE AND EXAMINE VENTILATION PATHWAYS. THE PROPOSED RESEARCH WILL ADDRESS FUNDAMENTAL SCIENCE GOALS OF THE NASA HURRICANE SCIENCE RESEARCH PROGRAM TO 1) BETTER UNDERSTAND THE COMPETING PHYSICAL PROCESSES THAT CONTROL HURRICANE INTENSITY CHANGE DURING TROUGH INTERACTIONS AND 2) QUANTIFY THE INTERACTION BETWEEN THE TROPICAL CYCLONE CORE AND LARGE-SCALE ENVIRONMENT. THE PRINCIPAL INVESTIGATOR (PI) AND CO-PI HAVE EXTENSIVE EXPERIENCE ANALYZING IN SITU AND REMOTELY SENSED OBSERVATIONS OF TROPICAL CYCLONES EXAMINING THE CONVECTIVE ASYMMETRIES GENERATED BY VERTICAL WIND SHEAR THE ROLE OF WIND SHEAR IN INTENSIFICATION AND THE VENTILATION OF THE TROPICAL CYCLONE INNER CORE. ADDITIONALLY ONE OF THE PIS DR. KRISTEN CORBOSIERO IS A FUNDED HS3 SCIENTIST AND ADVISES A NASA EARTH AND SPACE SCIENCE FELLOWSHIP AWARDEE INVESTIGATING THE ROLE OF OUTER RAINBANDS ON TROPICAL CYCLONE INTENSITY USING GRIP AND HS3 DATA.