Report on Stratosphere Task Force

Recognising the importance of the stratosphere for skilful seasonal and sub-seasonal prediction, the Stratosphere Task Force was set up in 2016 to improve the representation of the stratosphere in ECMWF forecast and analysis systems. This report synthesizes the most notable findings of the Task Force and provides recommendations for the way forward. The main focus is on: 1) Global-mean temperature biases; 2) Horizontal resolution sensitivity of the mid- to lower stratospheric temperatures; 3) Stratospheric meridional circulation and polar vortex variability; 4) Extratropical lower stratospheric cold temperature bias; 5) New sponge design; and, 6) Representation of tropical winds.