Abstract:
Systematic investigations of optical dayglow emissions at OI 557.7, OI 630.0, and OI 777.4 nm have been carried out simultaneously over a large field of view (~140°). These emission intensities are obtained during January–March in the years 2011 and 2012 from Hyderabad (17.5°N, 78.5°E), India, using a high spectral resolution multiwavelength imaging echelle spectrograph. Spectral analyses of planetary wave type periodicities in all the dayglow emission intensities are performed, and their association with lower atmospheric and direct solar forcings is presented. This analysis revealed that periods near the atmospheric free normal modes of 5, 10, 16, and 25 days (which are produced mainly in the troposphere) are found to register their presence in the upper atmospheric emission intensities. In an earlier study during high solar activity period (2001), sunspot numbers (SSNs) and the daily averaged OI 630.0 nm dayglow intensities were seen to be covarying. In contrast, the variability in the dayglow emission intensities during relatively low solar activity epoch (2011) shows no or weaker correlation with that of the SSN but a greater similarity with that of the equatorial electrojet strength. Periodicities of both lower atmospheric normal modes and those related to sunspots are found during moderate solar activity (2012). Based on this analysis, it appears that the upper atmospheric dayglow emissions respond mainly to lower atmospheric forcing during low solar activity, solar forcing in high solar activity, and both during moderate solar activity level.
