Title: The effect of latitude on jet variability

Abstract: The effect of latitude on eddy-driven jet variability is investigated across a range of data sets (i.e. Reanalyses, AR4 GCMs and a barotropic model). Eddy-driven jet variability is shown to be more persistent at equatorward latitudes compared to poleward latitudes, and the leading pattern of variability changes from a shift to a pulse as the jet is located closer to the pole. Both effects are linked to the sphericity of the earth, which influences eddy propagation and inhibits wave breaking on the poleward flank of the jet, decreasing the positive feedback between the eddies and the mean flow. Similar wave breaking arguments can explain the behavior of the eddy-driven jet in the presence of a strong subtropical jet and profiles of Rossby-wave breaking frequency on pressure surfaces illustrate this mechanism. These results explain why GCMs with jets too far equatorward relative to observations over-predict the timescale of Southern Annular Mode events and suggest that the leading mode of zonal-wind variability will transition from a shift to a pulse as the eddy-driven jets move poleward with climate change.

Speaker website: http://www.atmos.washington.edu/~eabarnes/

Host: Marty Singh (mssingh@mit.edu)