How does topography affect wind currents?
When the topography affects the weather, it is often called an orographic effect, from -oro that means ‘mountain’ in Greek. We are then talking about orographic fog, orographic convections and sometimes, katabatic and anabatic winds. The former is when cold air sinks from the hills down in the valley, at night, and the latter is the opposite, during daytime. As you understand, the wind cannot go through a hill or a mountain; it has to rise over it, to come down after it. That creates an undulation in the flow of the air that certainly affects a hot air balloon. Sometimes, at the lee of a mountains, you can see cumulus lenticularis clouds. Those are shaped like a lens and don’t move. They are made from air that rises and sinks as an eddy. This is often used by glider pilots to gain altitude from taking it from the rising side. A hot air balloon would the the same but, unfortunately, you can’t direct it. Even clouds tend to go up and down over the hills. I fly often my little airplane, h
