A new numerical model of the middle atmosphere. 1. Dynamics and transport of tropospheric source gases

It is shown that explicit computation of the planetary-scale wave field yields a more realistic representation of the zonal mean dynamics and the distribution of trace chemical species. In particular, wave breaking produces a well-mixed "surf zone' equatorward of the polar night vortex and drives a meridional circulation with downwelling on the poleward side of the vortex. This combination of mixing and downwelling produces shallow meridional gradients of trace gases in the subtropics and middle latitudes, and very steep gradients at the edge of the polar vortex. Mixing ratios of trace gases of tropospheric origin are very low within the vortex in winter. Computed distributions of methane and nitrous oxide are shown to agree well with observations. -from Authors