tonyotony: You need to rearrange your thinking just a tad. Think of what happens when the sun comes up. As soon as it starts hitting the treetops, the sun will start warming air that in turn will suck more and more air upward. However, before the sun really gets to working, the general flow of air will be downhill, hugging the ground. I would generally fix the time that things change over to the point where I start to feel the sun's heat.
Let's just say the sun rises at 7, and there's no wind. You're in a blind on top of the hill, overlooking a ravine. From the time you get to your blind until probably 0900 the airflow will be down hill in front of you. After that, it'll reverse and start coming back up into your face.
If you're in the bottoms, the general airflow pattern until 0900 will be mostly stagnant. Your body heat will carry the scent upwards. However, once the sun starts warming the hilltops, the draft will cause swirling and the flow will be generally uphill towards the part that's getting the most sun.
Now let's say its afternoon. The draft has been coming uphill all day. On the hilltop, there will be a marked shift as the sun sets. As soon as the lower elevations stop getting sun, the air will cool and sink, sucking air downhill from the top. Down in the bottoms, there is again this swirling as the flow adjusts. If you're in a fairly tight ravine, you'll also get a flow generally down and out of the bottom of the ravine.
On flat ground, things change, but it's still all powered by the sun. Let's say you're hunting a field surrounded by woods. The air in the middle of the field has been unprotected all night, and has cooled more than the protected woods. The air from the center of the field will try to find the lowest point it can, sucking air from the surrounding woods in over the top of the cooler air. When the sun hits the treeline at the edge of the field, the flow will change. When the sun hits the center of the field, it'll change still again. If you're hunting the edge of that field, you may encounter several changes from 0600 to 1000, and then again at 1600 until dark.