Theoretical Foundation of the Linear Relationship between the Midlatitude Eddy Heat Flux and Fall-to-Spring Polar Ozone Build-up


It has been demonstrated that there is a globally unified linear relationship between the interannual variations of the fall-to-spring polar ozone accumulation and the winter mean poleward eddy heat flux on the 100 hPa pressure surface. The foundation of this relationship is investigated using time-slice experiments on a chemistry–climate model with two levels of ozone-depleting substances (ODSs). The features of the transport field are interpreted by decomposing the horizontal ozone flux caused by the residual circulation into contributing processes including the eddy heat flux with the aid of the Transformed Eulerian Mean momentum equation followed by rearrangement of terms. The linear relationship between the interannual variations of the fall-to-spring ozone build-up integrated poleward and above a reference point Pref on a meridional plane and the poleward eddy heat flux during the corresponding period at Pref is realized for each hemisphere implying that the inter-hemispheric unification should be treated with caution. This relationship is interpreted using the fact that the interannual variation of poleward ozone transport in the upper stratosphere is captured well by the vertical convergence of the constituent-based Eliassen-Palm (EP) flux (F̃) which is defined as the product of the constituent (ozone) mixing ratio and EP flux. The eddy momentum flux contributes to the meridional ozone transport in combination with the eddy heat flux in the form of the divergence of F̃, although it is not responsible for realizing the linear relationship. The dependence of the linearity on the location of Pref and ODS levels is discussed.