ALBERT

Description: In a case study of a remarkable Major stratospheric sudden Warming (MW) during the boreal winter 2008/09, we investigate how transport and mixing triggered by this event affect the composition of the whole stratosphere in the Northern Hemisphere. We simulate this event with the Chemical Lagrangian Model of the Stratosphere (CLaMS), with optimized mixing parameters and with no mixing, i.e. with transport occurring only along the Lagrangian trajectories. The results are investigated by using the tracer–tracer correlation technique and by applying the Transformed Eulerian Mean formalism. The CLaMS simulation of N2O and O3 with optimized mixing parameters shows good agreement with the Aura Microwave Limb Sounder (MLS) data. The spatial distribution of mixing intensity in CLaMS correlates fairly well with the Eliassen–Palm flux convergence and illustrates how planetary waves drive mixing. By comparing the simulations with and without mixing, we find that after the MW poleward transport of air increases not only across the vortex edge but also across the subtropical transport barrier. Moreover, the MW event also accelerates polar descent and tropical ascent of the Brewer–Dobson circulation. The accelerated ascent in the tropics and descent at high latitudes firstly occurs in the upper stratosphere and then propagates downward to the lower stratosphere. This downward propagation takes over one month from the potential temperature level of 1000 to 400 K.