Originally Posted by
StaceyF
Why does it take me >10hrs to fly to the Carribean from the UK but <9hrs to fly back?
I'm guessing Earth rotation?
Correct, but in a longwinded way.
Yes that's a pun but it's after Christmas so I am excused.
Because of the earth's rotation winds tend to flow from the west. This is caused by a combination of the atmosphere "slipping" relative to the rotating earth mass, and also the heating effects of the sun when it is exposed to the earth surface compared to nighttime when it is not. In addition to the westerlies, air tends to flow from the Equator to the poles as well.
Because of this (and forget any local weather systems passing through, up at jet altitudes you are above those) there is a constant westerly wind, so aircraft heading west are fighting a headwind while those coming east are gaining a benefit. Exactly the same used to happen in the days of sailing ships crossing the Atlantic.
Winds up at altitude are much greater than down where we live on the surface. To prove this just climb up to the top of a mountain peak. Rule of thumb is whatever the wind is at ground level it is double that 1,000 feet up. This is due to surface drag, which slows the wind nearest the surface down.
Because the winds are variable and change from hour to hour, there is much to be gained by predicting what the relative wind is on each side of your intended course, as it may be that you can gain by taking a different route. For example when going to the Caribbean you may notice that sometimes you route out direct over Lands End and Bermuda, whereas other times you are far to the north, and may indeed sometimes pass over Newfoundland, which is actually giving a shorter time that day, while those coming the opposite way are trying to get into the fast winds, especially the very strong but surprisingly narrow band called the Jetstream.
All other things being equal westbounds normally find it better to be further north than eastbounds. This is true crossing both the Atlantic and the Pacific - Hong Kong to New York for example routes across the Pacific and Canada coming east but often gets up over the North Pole going west. Major airlines have a whole department in Flight Operations who plan all this each day; if you have a meteorology degree from University they will be pleased to see you.