Movements of airglow structures within the intertropical arc observed from southern Kenya

6300 Å airglow observations from Olorgesailie, Kenya (1.6°S, 36.4°E) show two types of movement within the southern intertropical red arc. The arc moves as a whole equatorwards at a rate of 3–4° per hour before local midnight tending to reverse direction after midnight. The second movement is an east-west wave propagation with a wavelength of approximately 600 km and a velocity of 120–130 m s −1. The wavelike movements have properties similar to medium scale atmospheric gravity waves.