Tropical and extratropical influences on the variability of the southern hemisphere wintertime subtropical jet

The focus is on the austral winter season when the STJ is strongest and most distinct from the midlatitude eddy-driven jet (EDJ). Variations in the intensity and latitudinal position of the STJ are diagnosed using an index developed to discriminate between variations associated with the EDJ.

STJ intensity and position variations are found to be tied to different mechanisms. An intensification of the STJ is associated with enhanced divergent outflow from diabatic heating over the equatorial Pacific Ocean, primarily resulting from eastern Pacific or canonical El Nino. This intensification is associated with a narrowing of the STJ and an in-place weakening of the EDJ.