Rapid variation of the vertical component of air motion causing an aircraft to jolt alternatively upward and downward. Bumpiness is associated generally with either convection currents in an unstable atmosphere or a flow of air across surface irregularities or both. It is more common and intense over land than over the sea. It is most marked in the lowest kilometer of the atmosphere but may extend to much higher levels, especially over mountainous terrain. Different types of aircraft may experience different types and intensities of bumpiness when flying through identical atmospheric conditions.