Impacts of tropical tropopause warming on the stratospheric water vapor

We investigate the impact of tropical tropopause warming on the stratospheric water vapor using the Specified-Dynamics version of the NCAR Whole Atmosphere Community Climate Model. We find that the tropical tropopause warming results in a strengthening of the Brewer–Dobson circulation (BDC). The strengthening of BDC induced by a narrow warming of tropical tropopause within 12° latitude, which is much stronger in boreal winter than that in boreal summer, propagates more dry air from the tropical tropopause into the stratosphere and thus causes a reduction of water vapor in the middle stratosphere. On the contrary, the seasonal difference of the BDC strengthening is weaker in the experiment with a broader tropical tropopause warming within 25° latitude. The drying effect of the BDC is counteracted by the moistening effects of the tropical tropopause warming and methane oxidation. This leads to the moistening in both the lower and upper stratosphere. The results suggest the control of the stratospheric humidity by the tropical tropopause temperature could be significantly offset by the associated BDC changes.