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

Assessment studies of future supersonic aircraft impact on the chemical com position of the atmosphere have generally been made using two- or three-dim ensional chemical transport models (CTM). Typical products of these calcula tion 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 HSC T can produce significant anomalies in the lower stratospheric water vapour mixing ratio (about 10% at Northern mid-latitudes). Stratospheric H2O and O-3 absorb longwave planetary radiation, so that HSCT driven changes may up set the residual circulation and produce a radiative forcing at the tropopa use. A climate-chemistry model is used here to study this effect, using an iterative procedure for the chemistry and radiation modules that are not si multaneously interactive. The major findings are the following: (a) lower s tratospheric vertical fluxes of H2O and other atmospheric tracers are signi ficantly affected by water vapour and ozone radiative feedback on the strat ospheric circulation. (b) H2O accumulation patterns change significantly in the tropical lower stratosphere, with respect to the case with no radiativ e feedback on circulation of HSCT additional H2O and perturbed 03 (baseline case). (c) The tropopause radiative forcing of this additional water vapou r is greatly reduced with respect to the baseline case. (C) 2001 Elsevier S cience Ltd. All rights reserved.