WAVE BREAKING SIGNATURES IN OH AIRGLOW AND SODIUM DENSITIES AND TEMPERATURES .1. AIRGLOW IMAGING, NA LIDAR, AND MF RADAR OBSERVATIONS

The Collaborative Observations Regarding the Nightglow (CORN) campaign took place at the Urbana Atmospheric Observatory during September 199 2. The instrumentation included, among others, the Aerospace Corporati on narrowband nightglow CCD camera, which observes the OH Meinel (6-2) band (hereafter designated OH) and the O-2 atmospheric (0-1) band (he reafter designated O-2) nightglow emissions; the University of Illinoi s Na density/temperature lidar; and the University of Illinois MF rada r. Here we report on observations of small-scale (below 10-km horizont al wavelength) structures in the OH airglow images obtained with the C CD camera. These small-scale structures were aligned perpendicular to the motion of 30- to 50-km horizontal wavelength waves, which had obse rved periods of about 10-20 min. The small-scale structures were prese nt for about 20 min and appear to be associated with an overturned or breaking atmospheric gravity wave as observed by the lidar. The breaki ng wave had a horizontal wavelength of between 500 and 1500 km, a vert ical wavelength of about 6 km, and an observed period of between 4 and 6 hours. The motion of this larger-scale wave was in the same directi on as the approximate to 30- to 50-km waves. While such small-scale st ructures have been observed before, and have been previously described as ripple-type wave structures [Taylor and Hapgood, 1990], these obse rvations are the first which can associate their occurrence with indep endent evidence of wave breaking, The characteristics of the observed small-scale structures are similar to the vortices generated during wa ve breakdown in three dimensions in simulations described in Part 2 of this study [Fritts et al., this issue]. The results of this study sup port the idea that ripple type wave structures we observe are these vo rtices generated by convective instabilities rather than structures ge nerated by dynamical instabilities.