The "Ground Effect", "Pressure Waves" and surfing pelicans The weather is cold and overcast and I am a stay behind in our 12th floor rental on the beach this afternoon while the wife and sister are shopping the outlet malls. I made a new (to me) observation from the balcony: pelicans not only use the ground effect to skim over the surface of the water, they use high pressure air waves created by mechanical waves in the surf to "surf" the air above the waves. I had never really noticed this from ground level and had never really paid attention to it before from an appropriate height and angle to see what the birds do. They glide just in front of a rolling wave, (in a high pressure up draft) until the wave crests (and the air becomes turbulent), then they flap and fly diagonally outward to the next roller, then they glide, etc. etc. So, they not only use the passive aerodynamic advantage of ground effect, they also use the active effect of air pressure waves above the ocean's waves to their advantage.