Seasonal variations of emission characteristics of hydroxyl molecules with different vibrational excitation

Hydroxyl emission characteristics are under influence of aeronomical processes in the mesopause region. Therefore the ground-based observations of the rotation - vibration OH bands give some information about these processes. Spectrographical measurements of the hydroxyl emission spectrum in the infrared region have been made at the Zvenigorod Observatory (56N, 37E), Russia during more four decades. In this paper, the data on the observations for 2000 to 2001 are analyzed to derive seasonal variations of rotational temperatures and intensities of different OH bands. The analysis showed that the basic features of the seasonal variations are as follows. (1) Amplitudes of the annual and semiannual intensity variations of the emissions from the higher vibrational levels (v>6) of the hydroxyl are approximately 18 % and 7 % of the corresponding mean annual intensities. The intensity variations of the emissions from the lower vibrational levels (v<6) are characterized by the annual and semiannual harmonics with amplitudes of about 11 % of the mean annual intensities. (2) The mean annual rotational temperatures, derived from the bands arising from different vibrational levels, are close (for example, T(v=3) = 202 K, T(v=9) = 201 K). However, the temperature difference between T(v=3) and T(v=9) is significant in the periods close to summer and winter solstices and autumn equinox. (3) The maxima of the annual variations of the emission characteristics from the higher vibrational levels lead those from the lower vibrational levels.