Very good skid, I suddenly remember this from a geography lesson:
Coriolus Effect
The deflective effect of Earth's rotation on all free-moving objects, including the atmosphere and oceans. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
1. Object moving north (or south) in N. hemisphere tends to deflect to the right; in S. hemisphere tends to deflect left
2. Why? It results from fact that at higher latitudes, any point on surface of Earth is traveling slower due to less circumference in direction Earth is rotating (WestàEast)
a. E.g., circumference at equator is 24,000 miles, so air mass at surface is traveling at 24,000 miles/day
b. At 45º N latitude, an object is traveling a circumference of Cosin 45º = 0.707, or ca. 17,000 miles/day
c. Thus, for example, south-moving air mass traveling at, say, 17,000 miles/day at 45º N. latitude encounters Earth underneath it rotating increasingly rapidly (westàeast) at lower latitudes, and “deflects right”
1. Right-deflected air masses in northern latitudes (ca. 0-30º N) cause “northeast trade winds”; southeast trade winds in corresponding S. latitudes
2. Prevailing (midlatitude) westerlies also result from Coriolus effect, but in this case from northward moving air masses within the “Ferrel Cell” (30-60º N. latitudes), again following “deflect right” rule