Dynamics of the polar mesopause and lower thermosphere region as observed in the night airglow emissions

This work utilizes night airglow emissions to deduce temperatures, dynamics, energetics, transport and photochemistry of the polar 80-110 km atmospheric region. The morphological behaviour of the polar 80-110 km region as seen in the night airglow emissions is best described by quasi regular to regular variations in the temperature and in the intensities of the emissions with periods ranging from minutes to a few days. Temperature amplitudes are seen from a few degrees up to ±50 K. Intensity changes up to several hundred percent may occur. Gravity waves from below are generally found to be present in the region, being responsible for much of the short period variations. The long period variations are seen to be related to circulation changes in the lower atmosphere. Stratospheric warmings are generally associated by a cooling of the 80-110 km region by a ratio approximately twice as large in amplitude as the heating at the 10 mbar level. The semidiurnal tide is found to be dominant with a peak to peak amplitude of about 5 K, in contrast to model calculations. Effects from geomagnetic phenomena on the energetics and dynamics of the region are not seen and, if present, have to be small or rare as compared to the influence from below. There is a mesopause temperature maximum at winter solstice. Pronounced differences in the day to day and seasonal behaviour of the odd oxygen associated nightglows at the North and South Pole are found. This may indicate fundamental differences at the two poles in the winter mesopause region circulation and energetics