Effects of convective ice evaporation on interannual variability of tropical tropopause layer water vapor

Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We break down the influences of the Brewer–Dobson circulation (BDC), the quasibiennial oscillation (QBO), and the tropospheric temperature (1T ) on TTL water vapor as a function of latitude and longitude using a two-dimensional multivariate linear regression. This allows us to examine the spatial distribution of the impact of each process on TTL water vapor. In agreement with expectations, we find that the impacts from the BDC and QBO act on TTL water vapor by changing TTL temperature. For 1T , we find that TTL temperatures alone cannot explain the influence. We hypothesize a moistening role for the evaporation of convective ice from increased deep convection as the troposphere warms. Tests using a chemistry– climate model, the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), support this hypothesis.