Impacts of future composition changes on stratospheric radiative damping rates in the UM-UKCA model

Previous studies have evaluated the approximation of local linear relaxation to a reference temperature state (i.e., “Newtonian cooling”) in the middle atmosphere in models and observations. Here we evaluate the validity of this approximation for both longwave and shortwave heating rates in the UM-UKCA model for the first time. We also investigate the impacts of projected future composition changes (e.g. Antarctic ozone recovery and increases in carbon dioxide concentrations) on radiative damping rates in the middle atmosphere. We present evidence for potentially important changes in the net radiative damping rates under increased greenhouse gas concentrations, particularly in the upper stratosphere. We further elucidate the sources of these changes using offline radiation codes and analysing species dependent heating rates from the online model.