My understanding is that this balancing out with gravity would be true, but for horizontal mixing that occurs, as well as downdrafts of cold air and radiation (

My understanding is that this balancing out with gravity would be true, but for horizontal mixing that occurs, as well as downdrafts of cold air and radiation (which is significant enough to motivate the chimney idea, according to the author). So you have this very complex voyage of ground-heated air upward, which is responsible for most of what we think of as local weather. I understand the idea is to streamline the updraft, essentially controlling weather in the immediate vicinity.