|MadSci Network: Earth Sciences|
This question is difficult to answer without knowing more about the particular geographical layout of this canyon and it's position with respect to surrounding bodies of water or mountains. However, that said, we do know that breezes often occur due to temperature and pressure differences between two areas. If you're by an ocean, in the mornings and evenings, the ocean and land heat and cool at different rates. Water and land have different heat capacities. This causes differences in the temperature of the air over the respective areas, and a resulting difference in local pressures. These temperature and pressure differences are equilibriated when the cool and warm air masses mix. Near the coast, this mixing of two air massess is witnessed as the commonly termed "sea breeze." It doesn't just have to be an ocean either. The only thing that matters is that two nearby areas have significantly differing effective heat capacities. It could also be something like a canyon. Deep inside the canyon, the sun doesn't penetrate deeply and transfer it's radiative forcing as quickly as in the open. Therefore, a hypothesis for your particular canyon may be that during the morning, the area outside the canyon heats up at a faster rate than inside the canyon. This may result in a temperature differential and felt as the rush of air. This also happens in the evenings, although in reverse direction, because the area in the open may cool faster (release it's heat to outer space) than the area deep inside the canyon. One question for you is: is the breeze noticeably weaker on humid days? Can you think of why this might be?
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