Wind.

The amount of influence that the wind will hold over the distribution and quality of a sound is determined by the wind gradient - the vertical gradient of the mean horizontal wind speed in the lower atmosphere. Above the ground, plants must adapt not only to the force of the wind, but to wind's constant fluctuations - the response of plants to wind is dynamic and constantly adapting to the environmental changes that wind creates. Scientists from the University of Arizona studied gigantic wind-formed ridges of rock, "yardangs", to discover that the eroding power of wind is sufficient to keep mountains from growing. FEATURES Simply expressed, wind describes the movement of air from areas in the atmosphere of high pressure to areas of low pressure. [Extracted from the article]