#PPOD: Lee waves are atmospheric gravity waves that form when stable air flows over significant topographic obstacles like mountains, volcanoes, or large crater rims. As the wind is forced upward by the terrain, it undergoes adiabatic cooling, causing water vapor or CO2 to condense into visible, ripple-like clouds on the downwind (lee) side. They often appear as "cloud trains" or straight, parallel lines perpendicular to the wind direction. Credit: ESA's Mars Express/ESA/DLR/FU Berlin

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