The signature of short-period gravity waves imaged in the OI [formula omitted] and near infrared OH nightglow emissions over Panhala

Abstract

With the development of cooled CCD detector, it has become possible to detect the spatial and temporal variation of the small-scale structure in airglow emission more accurately. Using tilting filter photometers ( 630 nm and OH) and a CCD-based multi-channel all-sky imager, the night airglow observations were carried out from Kolhapur (16.8°N,74.2°E) and Panhala (17.0°N,74.2°E; height above mean sea level 3200 ft ), India, during the clear and moonless nights of January–February, 2001. The multi-wavelength airglow imaging enables us to study the horizontal structures of the small-scale gravity waves at various heights in the region of emissions and to investigate propagation of those waves in detail. Hydroxyl (OH) and OI 557.7 nm images on the night of February 18, 2001 showed row-like structures moving from north to south direction spanning over 500 km in the sky. The observed horizontal phase speed (∼50 m/ s) , wavelength (∼25 km) , wave period (∼8 min) of the atmospheric gravity waves have been determined from a set of sequential images of OI 557.7 nm (at 97 km ) and OH (at 86 km ) observed at Panhala. These are the first observation of the signature of atmospheric gravity waves using an all-sky imager in Indian region indicating perturbation in density in the mesospheric region (80– 100 km ). The possible sources of the waves to the extended region have been discussed.