Which mechanism explains the formation of longitudinal sand dunes parallel to trade wind streams?

💡 Explanation

When wind blows over loose sand, wind-shear convergence creates helical flow because differential velocities produce turbulent eddies, leading to alternating zones of erosion and deposition aligned with the dominant wind direction. Therefore helical flow creates the parallel alignment, rather than Coriolis deflection, evaporation, or anchoring influencing the direction.

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