Why do the winds in the upper troposphere blow from west to east?

Question

In the midlatitudes of both the Northern and Southern hemisphere the winds of the upper troposphere blow from west to east. Why is this so?

Answer 1

Consider an idealized model of Earth as a non-rotational sphere with uniform solid surface. Since the sun heats the equatorial regions more intensely than the polar regions, a convection cell will develop in each hemisphere due to meridional temperature gradient on the sunny side of the globe. The planetary-scale air will then circulate between the equator and the poles such that warm (less dense) air rises at the equator, and flows toward the poles aloft, while cold (dense) air sinks at the poles and flows toward the equator at surface. If the idealized Earth begins to rotate, the Coriolis force will shift the surface winds to southwest in the Northern Hemisphere, northwest in the Southern Hemisphere.

now....

Midlatitude westerlies: the highly variable planetary-scale winds that blow from southwest in the Northern Hemisphere and from northwest in the Southern Hemisphere between 30 and 60 latitude. In middle- and upper-troposphere, midlatitude westerlies blow west to east in a wavelike pattern of ridges and troughs. These winds are responsible for the development and displacement of the weather systems (highs, lows, and air masses) and for the poleward heat transfer.

The tropopause is not continuous from poles to equator but occurs in discrete segments. The altitude of the tropopause is directly proportional to the mean temperature of the troposphere; therefore, it decreases with latitude.