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HOME > El Niño/La Niña > The ENSO Cycle > ENSO - Jetstream
Jet Stream Graphiics

During El Niño episodes there is a pronounced eastward extension of deep tropical convection and deep tropospheric heating to well east of the date line. This heating acts to extend the subtropical ridges in both hemispheres to well east of the date line, and to increase the north-to-south temperature difference along the poleward flanks of the subtropical ridges in this region. These conditions are generally most prominent during the respective hemisphere's winter season, when they contribute to 1) a pronounced eastward extension of the midlatitude jet stream to the extreme eastern Pacific, and 2) an equatorward shift of the jet streams over the eastern Pacific. Overall, these conditions reflect an increasing zonally uniform distribution of both temperature and winds across the Pacific basin, and are a major factor affecting the winter weather patterns and storm tracks in the middle latitudes over both North and South America.

During El Niño episodes, a large-scale upper-level anticyclonic circulation (A's) anomaly is evident in both hemispheres over the subtropical latitudes of the eastern Pacific. This anticyclonic anomaly dipole features enhanced westerlies along its poleward flanks in the middle latitudes of both hemispheres and anomalous easterly winds across the equatorial eastern Pacific. In the subtropics and middle latitudes, these anomalies reflect the eastward extension of the subtropical ridge noted above, as well as the eastward extension of the wintertime jet streams to well east of the date line. In the Tropics, they are consistent with a reduced strength of the equatorial Walker Circulation typical of El Niño episodes.

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