a narrow variable band of very strong predominantly westerly air currents encircling the globe several miles above the earth. There are typically two or three jet streams in each of the northern and southern hemispheres.
Sahilll Shakya answered this
The jet stream consists of ribbons of very strong winds which move weather systems around the globe.Jet streams are found 9-16 km above the surface of the Earth, just below the tropopause, and can reach speeds of 200 mph.
A. S. Anandakrishnan answered this
in the troposphere high altitude winds (above 12000 M) are known as jetstream.