Characteristics of gravity waves in the upper mesosphere region observed by OH airglow imaging

We present the characteristics of small-scale (<100 km) gravity waves in the upper mesosphere region derived from OH airglow imaging observations at Allahabad (25.4 degrees N, 81.8 degrees E, dip lat. similar to 16.34 degrees N) in India during January-May 2008 on cloud free and moonless nights. Horizontal and vertical propagation characteristics of the short period (<1 h) gravity waves (wavelength, apparent phase velocity, periodicity, direction) have been retrieved. Observed period, horizontal wavelength and observed horizontal phase speeds of gravity waves were typically 5-17 min, 10-37 km and 10-48 m/s. The propagation directions are in north and north-eastward in April and May. In February and March, few displays showed significant south-west motion. The possible source of wave generation has been discussed.