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 (T_CP), 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 T_CP, 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 T_CP 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 T_CP, and/or possible uncertainties in the satellite measurements.