Diagnosing Observed Stratospheric Water Vapor Relationships to the Cold Point Tropical Tropopause

Dehydration at the tropical cold point tropopause primarily controls the entry value of water vapor to the stratosphere, with additional (uncertain) contributions from subtropical monsoonal circulations and extreme deep convection. Here we quantify the links of observed stratospheric water vapor with near‐equatorial cold point temperature (TCP), based on interannual variations of monthly zonal averages over the period 1993–2017. Water vapor observations are from combined Halogen Occultation Experiment and Aura Microwave Limb Sounder satellite measurements, and cold point temperatures are from high quality radiosondes and GPS satellite data. Interannual water vapor anomalies are highly correlated with TCP, and coherent patterns can be traced in space and time away from the tropical tropopause to quantify transport in the Brewer‐Dobson circulation, including diagnosing seasonal changes in circulation. Lagged regressions with TCP are used to reconstruct water vapor variations directly tied to the cold point, and these reconstructions account for a majority of the observed interannual water vapor variability in the lower to middle stratosphere over most of the globe. Small systematic differences from observed water vapor can identify processes not tied to zonal average TCP, and/or possible uncertainties in the satellite measurements. Plain Language Summary Stratospheric water vapor is controlled by the freeze‐drying of air entering the stratosphere across the cold tropical tropopause, in addition to uncertain contributions from extreme deep convection and other processes. This work quantifies how interannual variations in water vapor measured by satellites during 1993–2017 are related to observed fluctuations in tropical tropopause temperature. We demonstrate strong correlations from the observations and use the evolution of correlation patterns to trace the transport of water vapor anomalies throughout the global stratosphere. We use the relationship with observed tropopause temperatures to estimate water vapor changes over time, and these calculations show excellent agreement with the satellite measurements over the entire globe. Our results demonstrate that tropopause temperatures exert a dominant control over global stratospheric water vapor. Key Points Strong correlations between observed stratospheric H2O and tropical tropopause temperatures trace the stratospheric transport circulation Stratospheric H2O reconstructed from tropopause temperatures explain