ATMOSPHERIC RADIATIVE EQUILIBRIA IN A SIMPLE COLUMN MODEL

An analytic radiative-equilibrium model is formulated where both short - and longwave radiation are treated as two-stream (down- and upward) fluxes. An equilibrium state is defined in the model by the vertical t emperature profile. The sensitivity of any such state to the model atm osphere's optical properties is formulated analytically. As an example , this general formulation is applied to a single-column Ii-layer mode l, and the model's optical parameters are obtained from a detailed rad iative parametrization of a general circulation model. The resulting s imple column model is then used to study changes in the Earth-atmosphe re system's radiative equilibrium and, in particular, to infer the rol e of greenhouse trace gases, water vapor and aerosols in modifying the vertical temperature profile. Multiple equilibria appear when a posit ive surface-albedo feedback is introduced, and their stability is stud ied. The vertical structure of the radiative fluxes (both short- and l ongwave) is substantially modified as the temperature profile changes from one equilibrium to another. These equilibria and their stability are compared to those that appear in energy-balance models, which here tofore have ignored the details of the vertical temperature and radiat ion profiles.