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Short Timescale Variability of the Mesospheric Sodium Layer
O'Sullivan, Créidhe; Redfern, R.M.; Ageorges, N.; Holstenberg, H.-C.; Hackenberg, W.; Ott, T.; Rabien, S.; Davies, R.; Eckart, A.
In this article we investigate the short-term characteristics of the sodium layer and their implications for laser guide star systems. We report measurements of sodium density and centroidheight variations on timescales of 100 ms upwards. Significant centroid-height variations on short timescales may necessitate frequent refocussing of the beam and wavefront sensor system.We present results from observations of the mesospheric sodium layer taken at the Max Planck observatory in Calar Alto, Spain in September 1997 and August 1998. We describe our experiment which uses the resonant optical backscatter of 589.2 nm laser light from the upper atmosphere as a measure of sodium abundance. Short-term variations are dominated by the formation of dense sporadic layers in the normal sodium layer. Measurements were made on 3 nights in 1997 and on 2 nights in 1998. Somewhat unexpectedly for a mid-latitude site, sporadic sodium layers were seen on 4 of these 5 nights. One of the sporadic layers was observed for its duration. The 2 km wide layer reached a maximum intensity of approximately two and a half times that of the background layer and could be distinguished from the background for over five hours. Centroid height variations of up to 400 m were observed on timescales of 1–2 min. In 1998 we were sensitive to variations of 5% or more in total sodium abundance on timescales of 100 ms upwards. We found no evidence for variations of this level on these short timescales.
Keyword(s): adaptive optics; laser guide star; mesospheric sodium layer
Publication Date:
Type: Journal article
Peer-Reviewed: Yes
Institution: Maynooth University
Citation(s): O'Sullivan, Créidhe and Redfern, R.M. and Ageorges, N. and Holstenberg, H.-C. and Hackenberg, W. and Ott, T. and Rabien, S. and Davies, R. and Eckart, A. (2000) Short Timescale Variability of the Mesospheric Sodium Layer. Experimental Astronomy, 10 (1). pp. 147-156. ISSN 0922-6435
Publisher(s): Kluwer Academic Publishers
File Format(s): other
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First Indexed: 2016-05-07 05:00:07 Last Updated: 2018-09-15 06:09:32