Recent progress in mesospheric gravity wave studies using nightglow imaging systems

During the past four decades a variety of optical remote sensing techniques have revealed a rich spectrum of wave activity in the upper atmosphere. Many of these perturbations, with periodicites ranging from ~5 min to several hours and horizontal scales of a few ten's of km to several thousands km, are due to freely propagating acoustic-gravity waves and forced tidal oscillations. Optical observations of the spatial and temporal characteristics of these waves in the mesosphere and lower thermosphere (MLT) region (~80-100 km) are facilitated by several naturally occurring, vertically distinct nightglow layers. This paper describes the use of state-of-the-art ground-based CCD imaging techniques to detect these waves in intensity and temperature. All-sky (180°) image measurements are used to illustrate the characteristics of small-scale, short period (< 1 hour) waves and to investigate their seasonal propagation and impact on the MLT region. These results will be contrasted with measurements of mesospheric temperature made using a separate imaging system capable of determining induced temperature amplitudes of much larger-scale wave motions and investigating night-to-night and seasonal variability in mesospheric temperature.