Why does El Niño enhance the jet stream? As quoted over here. This is especially interesting to me because El Niño tends to warm up the climate, and warmer climates are generally associated with weaker jet streams.


  El Niño has other effects further into North America. It tends to enhance the jet stream, creating a wall that prevents Arctic air (and the Polar Vortex) from dipping down to mid-latitudes. East Coast winters are generally drier and warmer during El Niño years, which is probably good news to those still smarting from this recent frigid season. The mild winter has interesting downstream effects, like a boost for the U.S. economy during the Christmas season.
I'm not sure if it's correct to say that El Niño enhances the jet stream, reading NWS
they seem to state that the affect is more of a shift in the position of the jet stream over the Pacific and North America. I guess any enhancement would be due to a greater temperature contrast between the poles and equator.