Climatic impact of future supersonic aircraft: role of water vapour and ozone feedback on circulation

Abstract

Assessment studies of future supersonic aircraft impact on the chemical composition of the atmosphere have generally been made using two- or three-dimensional chemical transport models (CTM). Typical products of these calculation are ozone profile and column changes produced by NOx, H2O and particle emissions from supersonic aircraft (HSCT). These have to be interpreted as pure chemical perturbations, being the atmospheric circulation kept fixed in the models. On the other hand, steady state accumulation of H2O from HSCT can produce significant anomalies in the lower stratospheric water vapour mixing ratio (about 10% at Northern mid-latitudes). Stratospheric H2O and O3 absorb long-wave planetary radiation, so that HSCT driven changes may upset the residual circulation and produce a radiative forcing at the tropopause. A climate-chemistry model is used here to study this effect, using an iterative procedure for the chemistry and radiation modules that are not simultaneously interactive. The major findings are the following: (a) lower stratospheric vertical fluxes of H2O and other atmospheric tracers are significantly affected by water vapour and ozone radiative feedback on the stratospheric circulation. (b) H2O accumulation patterns change significantly in the tropical lower stratosphere, with respect to the case with no radiative feedback on circulation of HSCT additional H2O and perturbed O3 (baseline case). (c) The tropopause radiative forcing of this additional water vapour is greatly reduced with respect to the baseline case.