THE JET STREAMS are fast-flowing eastward currents of air in the mid-latitudes of both hemispheres, with their cores at altitudes above 30,000 ft. (9,144 m.). Although they flow eastward, they are driven by the temperature contrast between the equator and the poles. Near the equator where surface temperatures are at a maximum, the air rises and, in the upper atmosphere, flows poleward. As the air moves away from the equator, the eastward winds increase in speed relative to the Earth's surface, becoming the jet streams in mid-latitudes. (This is a consequence of the conservation of angular momentum.)

The jet streams are most intense during the winter season when the temperature difference between the equator and pole is at a maximum. When too intense, they become unstable, ...