Evidence for direct solar control of the mesopause dynamics through dayglow and radar measurements

The day-to-day measurements of the daytime intensities of hydroxyl (OH) Meinel (8-3) band airglow emissions at 731.6 and 740.2 nm carried out from the equatorial station Thiruvananthapuram (8.5degrees N, 76.5degrees E, 0.5degrees dip) during the period of January-March 2001 have been investigated. This investigation provides evidence for the presence of a long period (approximate to16 days) wave modulating these intensities at the mesopause altitudes. Simultaneous radar measurements of zonal wind at similar to87 km, i.e. mesopause from Tirunelveli (8.7degrees N, 77.8degrees E, 0.33degrees dip), a location nearby, also reveal the presence of these long period oscillations. The daytime airglow and zonal wind undergo changes simultaneously. Similar modulations are seen in the solar 10.7 cm flux also preceding dayglow and wind variabilities by 4-5 days. It is inferred in the present case that the changes in the solar flux are the cause of the generation of this long period wave in the atmosphere below the mesosphere. The oscillations in the measured dayglow intensities in the mesopause region and the winds at similar to87 km are resulting from the modulation caused by this wave in this region after a delay of 4-5 days.