ATMOSPHERIC AND IONOSPHERIC RESPONSE TO TRACE GAS PERTURBATIONS THROUGH THE ICE-AGE TO THE NEXT CENTURY IN THE MIDDLE ATMOSPHERE .1. CHEMICAL-COMPOSITION AND THERMAL STRUCTURE

The aim of this first part of a series of two articles is to examine t he potentially important role of the changing atmosphere on middle atm osphere ionization. The period covered is the last glacial maximum to the middle of the next century. Important parameters of interest to th e ionization are changes in temperature and the concentration of sever al neutrals, especially H2O, NOx, H2SO4, CH3CN, aerosols, etc. This pa rt deals with the changes in all these neutrals and the temperature af fecting the ionization using an interactive two dimensional model of c hemistry, radiation and dynamics. This article constructs an input fie ld for article II which is devoted to changes in the middle atmosphere ionization. For the past, values of the forcing parameters are known whereas, for the future, we assumed scenarios for the forcing paramete rs and made simulations. Special attention has been given to highlight changes at 30 degrees N. The two dimensional model used here consider s 'frozen' circulation in the troposphere. Although increased thermal emission by perturbing the lower boundary temperature has been conside red while simulating for future, it is still a constraint in the prese nt model. (C) 1997 Elsevier Science Ltd.