Stratospheric Water Vapor Affecting Atmospheric Circulation

A consistent result of climate model simulations is the moistening of the stratosphere. Many models show their strongest changes in stratospheric water vapor in the extratropical lowermost stratosphere, a change which could have substantial climate feedbacks (e.g. Banerjee et al. 2019). 

However, models are also heavily wet-biased in this region when compared to observations (Keeble et al. 2020), presenting some uncertainty on the robustness of these model results. In this study, we examine this wet bias, showing that it is consistent across various models. We present the results of applying a fully-Lagrangian transport scheme (CLaMS) within the EMAC climate model, showing that water vapor distributions from the modified model are very similar to observations.

Addionally, we describe the sensitivity of the atmospheric circulation in the stratosphere and troposphere to the abundance of water vapor in the lowermost stratosphere, including the mechanism by which this occurs, and show that the related effects on atmospheric circulation are of similar magnitude as climate change effects.