[thedoc (OP)]

Alex Stewart asked the Naked Scientists:
   From your recent November 16 podcast.....

Chris - A flight time to America is different in duration to a flight time from America though for the reason the Earth is turning to an extent, isn't it?

...Andrew - It's partly because the Earth's rotating, partly also it's affected by the high altitude winds that either give you til wind or a head wind on the plane. But yes, the rotation of the Earth does make a difference to that.

This one is really hurting my brain.. in the absence of wind factors, you imply that the atmosphere is shearing noticeably at an elevation of 10,000 metres .. by how much? I would have thought metres per hour.
What do you think?

[alancalverd]

If there were no wind, a plane would in effect be swimming thorough a stationary pond of air. The rotation of the earth would not change the distance nor the airspeed.

However the fact that the equatorial air is moving faster than the polar air is important if a mass of polar air (cold, dry, dense, hence high pressure) begins to travel southward and displaces a mass of tropical air (warm, wet, low density, hence low pressure) which moves northward. The result is a cyclone, with westerly winds in temperate latitudes. These rather messy features tend to become more ordered at high altitude where convection from ground heating and energy release from water condensing and freezing, are less significant, and the result is a continuous westerly jet stream of anything up to 200 knots.

The trick of longhaul flying is to avoid the jetstream when travelling west and exploit it when travelling east, whilst keeping an eye on standard airways routeings and, as far as possible, flight schedules (arriving an hour early at Heathrow just screws up everyone else's day, so you may not be able to use the full tailwind). And the jetstreams don't quite follow lines of latitude - they wander about and sometimes appear at surprisingly low altitudes. I recall a turboprop flight from Stansted to Glasgow at 20,000 ft where we literally hovered at 200 kt over Lincoln for 30 minutes whilst my boss, on a jet from Heathrow at 32,000 ft and only about 30 miles west, arrived on schedule.     

[chris]

I recall a turboprop flight from Stansted to Glasgow at 20,000 ft where we literally hovered at 200 kt over Lincoln for 30 minutes whilst my boss, on a jet from Heathrow at 32,000 ft and only about 30 miles west, arrived on schedule.   

I guess that's why they call it "Easy Jet"?