"The Characterisation of the Mesospheric Sodium Layer Above Cerro Tololo"

The intrinsic properties and characteristics of the mesospheric sodium layer have come under intense investigation of late due to the layer's importance in producing sodium Laser Guide Stars (LGSs), and the increasing prevalence of such LGS systems on the world's leading telescopes. It is the knowledge of the mesospheric sodium layer's short and long term behaviour that will allow observatories to predict and maximize the performance of their respective LGS adaptive optics (AO) systems. For example, variation of the mean altitude of the sodium layer introduces a focus error that cannot be distinguished from optical turbulence and can lead to loss of AO performance.

While the sodium layer has been extensively investigated in the northern hemisphere, very little measurements of the sodium layer have been performed in Chile. What I will present are the results from a year long sodium monitoring run conducted by the 0.9 m and Curtis-Schmidt telescopes located at Cerro Tololo, from February 2001 to February 2002. This includes such information as the annual and short term altitude variation of the sodium layer, the equivalent width of the layer and the concentration of the sodium atoms. I will conclude on what these results mean for the use of the LGS system installed on Gemini South.