Atmospheric stability at 90 km, 78°N, 16°E
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2007
Received: 21 February 2006
Accepted: 10 October 2006
Published: 23 March 2007
We employ observations obtained from a meteor wind radar to derive ambipolar diffusion coefficients, neutral temperatures, temperature gradients and, subsequently, Brunt-Väisälä frequencies at an altitude of 90 km over Svalbard (78°N, 16°E). The derived values showed a good agreement with independent measurements at each step of the analysis. Current atmospheric models are based on sparse data obtained at such high latitude, so these results represent a viable alternative for incorporating in subsequent studies of atmospheric dynamics, particularly if the derived monthly variabilities are included. The Brunt-Väisälä frequencies are then combined with wind shear measurements to estimate horizontally averaged gradient Richardson Numbers (Ri). We find Ri to be consistently larger in summer than winter due to wind shears being similarly larger in winter and augmented by the inverse seasonal variation in Brunt-Väisälä frequency. These seasonal variations result in Ri indicative of dynamic stability in summer and instability in winter. The variabilities in wind shear and Brunt-Väisälä frequency are then included to—albeit more qualitatively—illustrate the distribution between stability and static and dynamic instabilities as a function of season, using a novel portrayal pioneered by Zink and Vincent (J. Geophys. Res., 109, doi:10.1029/2003JD003992, 2004). The resulting picture is discussed in the framework of current conceptions of distribution of turbulent energy dissipation with height and season and of current opinion of the mesopause structure at 78°N.