Variability and trends in UTLS temperatures and water vapor

A body of work has shown that there are trends and variability in stratospheric water vapor closely related to variability in tropical tropopause temperatures, upwelling variations, the quasi-biennial oscillation, and possibly volcanic aerosol loading and sea surface temperatures. Prior studies have also shown that stratospheric water vapor has a small but non-negligible effect on global radiative forcing; therefore it is key to understand both trends and long-term variations. In this presentation, we will examine both the relationship between tropical tropopause temperatures and stratospheric water for the time period where we have global lower stratosphere water vapor measurements (primarily since the early 1990s), as well as the relationship between tropical tropopause temperatures and assorted atmospheric indices for the longer time period where we only have temperature measurements. We will present results from climate model runs testing the impact of volcanic aerosol loading on UTLS temperatures and stratospheric water vapor. Using the climate model runs, we also isolate the impact of the QBO on tropical upwelling into the stratosphere. Using WACCM, we found that the tropical tropopause temperature annual cycle amplitude is smaller than observed by ~30% in a case run without QBO nudging, and explore the reasons for that and its impact on stratospheric water vapor.