Airglow meridional intensity gradients (MIG) that moved from east to west with the antisolar meridian have been observed during times of considerably magnetic activity. The magnitude of the gradient is around 0.1 R/km or more. We believe the MIG phenomenon develops as a result of a velocity gradient that is produced by the meeting of opposing meridional neutral winds. The northern wind system arises from the auroral heating at high latitude that produces meridional winds penetrating to low latitudes in the summer hemisphere. The southern wind system is produced by the equatorial midnight pressure bulge that is formed by the thermal tides of the lower atmosphere combined with the in situ forcing by EUV radiation absorption in the daytime. In a magnetic storm the merging of the two wind systems produces a sharp front over a latitudinal width of several hundred kilometers. North of the front the ionosphere is evated, and the airglow is weak. South of the front the ionosphere is depressed, and the airglow is inhanced with a surface brightness of the order of 100 R. The conceptual model that evolved from these observations accounts for the overall behavior of the MIG as well as the normal midnight collapse. a simple calculation shows that the MIG can be used to estimate the meridional velocity gradient as well as the magnitude of the winds in the midnight pressure bulge.