The difference in flight duration for East-to-West and West-to-East Flights is due to head and tail winds How are these winds generated?

Answer 1

Jet streams are fast flowing, relatively narrow air currents found in the atmosphere at around 11 kilometres above the surface of the Earth, just under the tropopause. They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and the warmer air to the south.The major jet streams are westerly winds (flowing west to east) in both the Northern Hemisphere and the Southern Hemisphere; this is due to the Coriolis Effect caused by Earth's rotation. The paths of the flows typically show a meandering shape, and these shapes themselves propagate east, at lower speeds than that of the actual wind within the flow. On international flights, the difference is even greater, and it is often actually faster and cheaper flying eastbound along the jet stream rather than taking the shorter great circle route between two points.http://www.crystalinks.com/jetstream.html