The difference between warm and normal ensembles for the mean fields of zonal wind and height indicate an eastward and equatorward extension of the mid-latitude Pacific jet, associated with a similar extension of the transient feedback on the mean flow as measured by the convergence of vorticity flux. The increase in high frequency (periods of ~2-10 days) transient kinetic energy in the eastern portion of the Pacific during El Niño extends across Mexico. The high frequency transient vertical and meridional sensible heat fluxes, and the low level diabatic heating and baroclinicity of the mean state (measured by Ri-1/2) also indicate an eastward and equatorward shift of the entire storm track complex in the GCM and the analyses. The shift is consistent with the increased mid-latitude shear during El Niño that accompanies the overall tropical warming.
While the GCM storm track shift has strong similarities to that in the analyses, the GCM's large systematic errors in the mid-Pacific (eastward extension of the Pacific jet and the storm track) lead to an underestimation of the response to El Niño which has a very similar form. However, the GCM also shows a spurious tendency to move the storm tracks equatorward in the far western Pacific, as seen in the large positive anomalies in all dynamical indicators of the storm tracks at latitudes 20°-30°N.
last update: 26 October 1995
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