Originally Posted by kevinsac
..doesn't the answer have to do with the earth's rotation. The planet rotates from east to west. Even with absolutely no winds, the flight from SFO to BOS would be shorter..
It does but not in the way you allude to it here: the atmosphere is part of
the system Earth and rotates with the Earth. You have to keep in mind that
the air around the Earth is extremely thin, with the dense part more than
1000 times slimmer than the diameter of the planet, so the Earth does not
rotate in an 'ocean of air'.
But it still is caused by rotation: the higher air masses tend to drift from the
warmer equatorial regions to the cooler poles and during that movement, the Coriolis force (a force component orthogonal to the centrifugal force caused
by rotation and inertia) bend the direction of the flow. In the Norther
hemisphere that happens quite reliably from West to East.
Of course the scenario is more complex as the air has to flow back at some
stage someway and the 'hot spots' on the Earth move during the day and
season cycle.
Oceans also disrupt the naive model of jetstreams - Australia has reliable
West East jetstreams despite being in the Southerm hemisphere.
..after take-off in SFO, the earth is rotating towards you......in essence, Boston is moving closer towards you...
Actually no - if you stood in a resting system above the Earth's surface, the
you would appear to be travelling West, so hovering above SFO, Japan and
Russia would move towards you.