Stratospheric transport by stationary planetary waves ‐ the importance of chemical processes

Abstract

AbstractThe transport of reactive trace gases by stationary planetary scale waves has been investigated with the aid of Matsuno's stationary planetary wave model (1970) and the linear eddy equation derived from the tracer continuity equation. It is shown that, for stationary fluxes, K‐theory fields, as introduced by Reed and German (1965), may be defined. These become matrix fields when photochemical coupling effects are considered. The eddy flux of a particular trace gas is related to the gradients of the mean concentrations of the other chemically coupled trace gases, as well as to the gradients of its own mean concentration. In the special case of a chemically inert tracer our treatment indicates Kyy = Kxx = 0 and Kyx = – Kxy in contradiction to the results obtained by Reed and German (1965) but in agreement with recent results of Clark and Rogers (1978) and Matsuno (1980). The consequences of photochemical coupling effects for eddy fluxes are investigated quantitatively for two simple chemical schemes involving the pairs O3 and NOx, and NO and NO2. These effects are shown to be significant especially for NO and NO2 whose photochemical time‐constants are short. Furthermore, even in regions of the atmosphere where coupling effects become small, such as the lower stratosphere for O3 and NOx, the uncoupled K‐fields are quite different for various species indicating a source of error in current 1‐ and 2‐dimensional photochemical models. The relative importance of dynamical and chemical contributions to the uncoupled K‐fields is dependent on the characteristic time‐scales for photochemical and zonal advection processes. The relation of our work to a Lagrangian description of the transport process is discussed.