Temperature variation at mesopause levels during winter solstice at 78°N

Abstract

Atmospheric temperatures from the polar mesopause are deduced from spectrophotometric measurements of hydroxyl bands and lines in the night airglow made at 78°N during December and January 1980/81 and 1982/83. An overall mean temperature of 220 K is found with a range from 172 to 257 K in the daily mean values. Several warm periods lasting 3–6 days may be due to heat dissipated by gravity waves. One week of consistently low temperatures was apparently connected to a stratospheric warming. Both datasets show a warmer mean temperature later in January than for early and mid-December. The polar OH airglow seems to peak at or just above the mesopause. The data also indicate that the mesopause is situated at approx. 90 km with an upper temperature gradient of 1 K km −1 indicating a very shallow mesopause. A superposed epoch analysis of 19 consecutive 24-h periods reveals a semidiurnal variation in the temperature around winter solstice with an amplitude of 5 K. No diurnal variation of amplitude greater than 1 K is apparent. Average wind velocity deduced from the amplitude of the semidiurnal temperature variation is 9 m s −1.