Springtime transitions in mesopause airglow and dynamics: photometer and MF radar observations in the Scandinavian and Canadian sectors

• Published in: Journal of Atmospheric and Solar-Terrestrial Physics
• Main Authors: Manson, A.H., Meek, C.E., Stegman, J., Espy, P.J., Roble, R.G., Hall, C.M., Hoffmann, P., Jacobi, Ch.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2002
• Subjects: Physics; Atmospheric Sciences; Tromso
• Online Access: http://nora.nerc.ac.uk/id/eprint/13548/; http://www.sciencedirect.com/science/article/pii/S1364682602000640

Observations from 2 optical ground stations and 3 MF radars at high and mid-latitudes have been combined to describe "springtime transitions" in atomic oxygen and the mesopause wind fields and waves for eight years (1991-1998). The typical signature in the Stockholm (60degreesN, 20degreesE) OI 558 nm 'green-line' emission involves a rapid (circa) 2-days rise in the nighttime value by factors of 2 or so, with a subsequent decrease by factors of 3-10. There is considerable inter-annual variability in these green-line emissions, and also the hydroxyl airglow (intensities and temperatures) at Bear Lake Observatory (Utah, 42degreesN, 115degreesW), but the 6-8 year means do show a characteristic airglow "springtime transition" (AST) near the end of March. MF radars from Tromso (70degreesN, 19degreesE), Juliusruh (55 N, 13 E) and Saskatoon (52degreesN, 107degreesW) demonstrate springtime reversals in the mean (daily) zonal winds at 85-95 km, both annually and in B year means, at times near the airglow "transitions". The "tongue" of easterlies (near March 30) is a long-established feature of mesopause dynamics, and clear indications of associated changes in tides and gravity wave fluxes are also presented. The TIME-GCM is also used to investigate the characteristics of the airglow and winds during the interval associated with the AST events. Useful similarities with the observed variations are demonstrated.