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This is the first page of Part 2 of the Wind and Pressure module. In Part 1, we considered a sea breeze situation and analyzed the effects of pressure gradients, friction, and vertical motion. I didn't really go into the Coriolis force, because the Coriolis force doesn't play as big a role in the sea breeze as the other two forces.
Near the equator, the pressure gradient and friction tell the whole story. Because the orientation of the Earth is not constantly changing at the equator, the coriolis force is zero there. But here in midlatitudes, the coriolis force also affects the sea breeze.
Remember from the forces module that the Coriolis force is related to the fact that a "straight" path on the surface of the Earth actually curves as the Earth rotates beneath the air parcel (or ball). It's as though a force is acting to deflect the parcel to the right. This force's strength is directly proportional to the wind speed, and it is oriented to the right of the wind direction at any instant. So if we have this moving air crossing the coastline, the coriolis effect causes it to accelerate toward the right, changing its direction.
How much does the wind direction change? Enough so that, in mid to late afternoon in midlatitudes, the sea breeze ends up blowing at a 45 degree angle to the coastline, rather than directly onshore.
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