In synoptic scale weather systems (hurricanes and large mid-latitude storms), the Coriolis force causes the air to rotate around a low pressure center in a cyclonic direction. The air flowing around a hurricane spins counter-clockwise in the northern hemisphere, and clockwise in the southern hemisphere (as does the earth, itself). In both hemispheres, this rotation is called cyclonic. If the earth did not rotate, the air would flow directly in towards the low pressure center, but on a spinning earth, the Coriolis force results in the are arcing in towards the low pressure center. The coriolis force is of much too small a magnitude to have any relevance to the direction of rotation in a sink or toilet.