Science Update: Seasonality above the tropical tropopause: reconciling the Eulerian and Lagrangian perspectives of transport processes

M. Abalos and co-authors investigate recent contrasting results regarding the seasonality of ozone about the tropical tropopause in a new ACPD article. In the literature, different methods (Lagrangian versus Eulerian, and isentropic versus pressure vertical coordinates) yield different results in terms of ozone transport, and the results must be carefully compared in equivalent terms to avoid misinterpretation. By examining the Lagrangian calculations in the Eulerian formulation, they show that the results are in fact consistent with each other and with a common understanding of the ozone transport processes near and above the tropical tropopause. The analysis of the Transformed Eulerian Mean ozone budget indicates that the annual tropical upwelling cycle is the main forcing of ozone seasonality at altitudes with large vertical gradients in the tropical lower stratosphere. Using a Lagrangian framework, it is found that a large fraction (~50%) of the ozone molecules ascending through the tropical lower stratosphere is of extra-tropical origin and has been in-mixed from mid-latitudes. The full abstract can be found here.