Satellite-Observed Composition Change from Tropical Cyclones in the Upper Troposphere and Lower Stratosphere

Tropical cyclones (TCs) are known for a variety of impacts, including threats to life and property. However, an understudied impact in tropical cyclones is their effect on the chemical composition of the upper troposphere and lower stratosphere (UTLS). The transport of air between the troposphere and stratosphere, known as stratosphere-troposphere exchange (STE), is known to occur within TCs, but remains poorly understood. STE is important because it involves key greenhouse gasses that are prevalent in the stratosphere and troposphere and whose impact on Earth’s radiation budget and climate is most sensitive to changes in UTLS composition, such as ozone and water vapor.

This project examines observations of STE in TCs and its relationship 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 from the International Best Track Archive for Climate Stewardship (IBTrACS) and background conditions from MERRA-2 reanalysis data. Specifically, UTLS composition change is diagnosed using water vapor (H2O) and carbon monoxide (CO) as tropospheric tracers and ozone (O3) as a stratospheric tracer.

Preliminary results show that concentrations of H2O is enhanced by TCs throughout most of the UTLS (and oftentimes reduced in close proximity to the tropopause), O3 is reduced greatly in the upper troposphere, and CO is weakly enhanced in the upper troposphere. All diagnosed UTLS composition changes demonstrate significant sensitivity to the profile distance from TC center and TC intensity. Additionally, we have found that basin-specific differences in background conditions are important to consider to provide an accurate picture of UTLS composition changes within a TC.