The stratospheric circulation in a high-top and low-top version of the Met Office climate model

Model simulations show that the strength of the stratospheric meridional circulation will increase under climate change. Using an age of air tracer, and an online calculation of the residual mean circulation, stratospheric age of air and mass upwelling from troposphere to stratosphere in the tropical pipe are diagnosed using a high--top (stratosphere resolving) simulation and an equivalent low--top simulation run at the Met Office Hadley Centre. The results are validated against the residual circulation calculated from the ERA-Interim reanalysis. The importance of including a well resolved stratosphere for correctly simulating stratospheric transport is discussed.