Seasonal variations in the mesopause temperature over Yakutsk (63°N, 129.5°E)

Results of mesopause temperature measurements, performed with the infrared digital spectrograph at Maimaga station (63degrees N, 125degrees E) 150 km north of Yakutsk, have been presented. The atmospheric temperature at the mesopause altitude (similar to87 km) was determined from the emission rate distribution in the OH(3,0) and OH(6,2) bands. The average temperatures were estimated for 217 nights from August 1997 to April 2000 in order to analyze the seasonal temperature variations. When comparing the measured temperature with the atmospheric temperature at the 87- km altitude estimated with the use of the CIRA-86 and MSIS-90 empirical models, it turned out that both models describe well the variation in the mesopause temperature regime at a latitude of similar to60degrees in winter months, but the actual temperatures differ from model values in early spring and late fall. It has been found that the form of the seasonal temperature variations at an atmospheric altitude of 87 km, observed at high-latitude stations, differ from such variations at midlatitudes. The temperature maxima are observed in late fall and early spring at high latitudes and in the middle of winter at midlatitudes.