Upper Troposphere Lower Stratosphere Composition Change in Tropical Cyclones: Assessments from 17 Years of Satellite Observations

Abstract

Tropical cyclones (TCs) are known for a variety of impacts, including threats to life and property, although their effect on the chemical composition of the upper troposphere and lower stratosphere (UTLS) remains understudied. The transport of air between the troposphere and stratosphere, known as stratosphere-troposphere exchange (STE), involves greenhouse gases such as ozone and water vapor whose impact on Earth’s radiation budget and climate is most sensitive to changes in UTLS composition. Therefore, we examine observations of STE in TCs and relate these changes to TC and environmental characteristics. We utilize 17 years of trace gas profiles from the Microwave Limb Sounder (MLS) aboard the Aura satellite in conjunction with TC track information and environmental data to relate UTLS ozone and water vapor changes to TC intensity, distance from TC center, and environmental wind shear. We find that accounting for varying tropopause heights and basin-specific background composition is important to accurate assessment of UTLS composition changes within a TC. We also find that TCs are associated with increased water vapor throughout most of the UTLS and dehydration at tropopause level, while ozone is reduced greatly in the upper troposphere. All diagnosed UTLS composition changes demonstrate significant sensitivity to distance from TC center and TC intensity. Additionally, we find that TC-induced UTLS H$_2$O changes are highly dependent on shear magnitude, where weaker shear is associated with more pronounced tropospheric hydration and tropopause dehydration.