Gales in Wigton again today! One of my classes asked me what causes wind. The answer is basically convection. Hot sunshine on the Equator makes air expand, become less dense and float upwards. What goes up must come down. In the Northern Hemisphere it comes down over the latitudes of the Sahara desert. Then at ground level it flows back to the Equator. There is another cell like this taking air up from Europe and down over the Arctic. It is symmetrical in the two hemispheres. It is the joing up at ground level to complete the loop that gives us our winds. They don't go north/south because of the turning Earth but that's another story.
