Abstract
Abstract. The day-to-day measurements of the daytime intensities of hydroxyl (OH) Meinel (8-3) band airglow emissions at 731.6 and 740.2nm carried out from the equatorial station Thiruvananthapuram (8.5° N, 76.5° E, 0.5° dip) during the period of January-March 2001 have been investigated. This investigation provides evidence for the presence of a long period (≈16 days) wave modulating these intensities at the mesopause altitudes. Simultaneous radar measurements of zonal wind at ~87km, i.e. mesopause from Tirunelveli (8.7° N, 77.8° E, 0.33° 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 10.7cm 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 ~87km are resulting from the modulation caused by this wave in this region after a delay of 4-5 days.
Highlights
The understanding of the aeronomy at and around the mesopause altitudes has significantly improved in the last decade
Significant long period oscillations (∼16 day) in the OH dayglow intensity and the zonal wind have been observed with a time delay of 4–5 days, following similar variations in the solar flux, as seen in the 10.7 cm solar flux index
The observed phases of westward deceleration of zonal wind and the ∼16-day period involved, indicate this to be a planetary wave having eastward momentum. This wave seems to have originated in the lower atmosphere, i.e. stratosphere/troposphere, as a consequence of the changes in the solar flux and propagated upwards as the phase of Semi Annual Oscillation (SSAO) for this period is eastward
Summary
The understanding of the aeronomy at and around the mesopause altitudes has significantly improved in the last decade. The daytime airglow intensity measurements were made using Multi Wavelength Dayglow PhotoMeter (MWDPM) on two rotational lines at 731.6 and 740.2 nm in the OH Meinel (8–3) band at Thiruvananthapuram (8.5◦N, 76.5◦E, 0.5◦dip) during January-March 2001 for a period of 47 days. The three independent parameters, i.e. daytime Hydroxyl airglow intensity, zonal wind at ∼87 km and the solar F10.7 cm flux, all having important implications in the dynamics and energetic of the MLTI region, exhibit similar variability seemingly under the influence of a dynamical forcing present in this region. These observations are discussed, with the perspectives of MLTI energetics and dynamics
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