Types of wind

Jetstreams

Jetstream blowing over Egypt and the Red Sea. The Red Sea is on the top of the image, the Nile lies in the center. (Image from Whirling winds of the world)

Jetstreams are long bands of very strong wind. They occur at places where the contrast between hot and cold is very large, so where polar and tropical air meet.
Jetstreams occur generally at an altitude of 30,000 - 40,000 feet (9-11 km or about 6 miles). They can be 240 kilometres (150 miles) wide and 1600km (1000 miles) long. The speed of a jet stream can be up to 400kph (250mph).
Jetstreams are strongest in the winter, when they have moved to the equator and differences in temperature are larger. The jetstreams are weakest in the summer, when the differences in temperature are low and they have moved towards the poles.