What Is the Jet Stream

What is the jet stream?

A) a high speed stream of high altitude air between warm equatorial air and cool air to the north
B) a high speed stream of air carried east to west by the high-altitude trade winds
C) a stream of air confined between cold air in the upper atmosphere and warm air below
D) an intermittent stream of air generated by unusual cases of warm air masses north of cold air masses
E) a high speed stream of air circulating high-pressure cells