Effect of latitude on the persistence of eddy‐driven jets

Abstract

An asymmetry in the persistence of the eddy‐driven jet is demonstrated, whereby the equatorward‐shifted (low‐phase) jet is more persistent than the poleward‐shifted (high‐phase) jet. The asymmetry is investigated by stirring the non‐divergent vorticity equation on the sphere and is shown to arise due to the sphericity of the earth, which inhibits poleward wave breaking when the jet is at high latitudes. This spherical effect becomes increasingly important as the mean jet is positioned at higher latitudes. The persistence of the annular mode decreases as the mean jet moves closer to the pole due to the decreased persistence of the high‐phase state, while the low‐phase state exhibits similar persistence regardless of the jet position. These results suggest that with the expected poleward shift of the jet due to increasing greenhouse gases, the annular mode's total persistence will decrease due to a decrease in the persistence of the high‐phase.