Observed Long-Term Changes in Global Tropopause Characteristics

Abstract. Variability or long-term change in tropopause characteristics has important implications for climate, especially since its temperature – to a large extent – dictates the amount of water vapor (a critical greenhouse gas) in the stratosphere. While conventional observations sufficient for examining tropopause characteristics provide limited geographic coverage, the growing global navigation satellite system radio occultation record provides relatively unlimited geographic coverage continuously since early 2001. This study applies the temperature lapse-rate tropopause (LRT) and potential temperature gradient tropopause (PTGT) definitions to the most recent 23-year radio occultation data period (2003–2025, inclusive) to create robust climatologies and assess long-term changes (statistically significant positive/negative trends) in the altitude, temperature, and sharpness of the primary tropopause and in the occurrence of multiple tropopauses. Regardless of definition, primary tropopause altitudes and temperatures are found to be increasing in most locations globally, consistent with other studies. A narrow region of decreasing tropopause altitudes in the subtropics and over the southern hemisphere east Pacific ocean basin is found to be driven by localized tropical narrowing, while the width of the tropics (based on tropopause altitude) is found to be increasing otherwise, especially throughout the northern hemisphere. Primary tropopause sharpness is also found to be increasing in most locations, but especially so in the tropics, where it is driven by both upper troposphere stability decreases and lower stratosphere stability increases. Finally, double and triple tropopauses are becoming more frequent in both the tropics and midlatitudes.