Question

what are Jet streams

Answer 1

here is your answer user they are fast flowing relatively narrow air currents found in the tropopause and are located at 10 to 50 km .
hope this answer helpful for you.

Answer 2

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.