Tropical Cold Point Tropopause Temperatures

Stratospheric water vapor plays an important role in regulating Earth’s surface temperature and the concentration of stratospheric ozone, which protects life from harmful ultraviolet radiation. In the tropics, the coldest point in the atmosphere — the tropical cold point tropopause (CPT) — acts as a critical gateway that controls how much water vapor enters the stratosphere. Even small changes in CPT temperature can lead to significant impacts on climate, weather, and stratospheric ozone levels. This project aims to improve scientific understanding of the processes that shape the temperature of the CPT. Because changes in CPT temperature can influence tropical rainfall, cyclones, and convection, the results of this study are also relevant to understanding regional weather extremes. In addition, the project will support the Ph.D. research of two graduate students, providing valuable training for the next generation of atmospheric scientists. The goal of this project is to better understand the physical and dynamical processes that govern year-to-year changes in tropical CPT temperature. The investigators hypothesize that tropical CPT temperature responds to warming in the tropical troposphere through two competing mechanisms: radiative heating and dynamic cooling. These effects largely cancel out on interannual time scales, though not necessarily on seasonal or decadal scales. A second hypothesis addresses an unexplained relationship between tropical CPT and stratospheric temperatures, which may be related to the Brewer-Dobson Circulation (BDC), the deep overturning motion of the stratosphere. To test these hypotheses, the research team will analyze satellite observations, including high-vertical-resolution GPS radio occultation (GPS-RO) temperature data, modern atmospheric reanalyses, and simulations from chemistry-Earth System and radiative transfer models. This integrated approach will improve understanding of tropical CPT variability and help to resolve conflicting evidence in current Earth system research regarding its drivers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.