5 Conclusion

The atmospheric seeing at the South Pole has been measured during a campaign of 15 balloon launches from June-August 1995. The vertical $C_{\rm N}^{2}$ profiles indicate the presence of an highly turbulent boundary layer up to an altitude of 100-250 m, with a very stable free atmosphere.

The boundary layer turbulence is closely associated with the katabatic wind and surface temperature inversion (Fig. 5). This suggests that the seeing at other sites higher on the plateau, where the katabatic wind is absent, is likely to be substantially lower than the average $1.86\hbox{$^{\prime\prime}$}$ ($1.36\hbox{$^{\prime\prime}$}$ at 2.4 $\mu$m) from surface level at the Pole, and may well approach the $0.37\hbox{$^{\prime\prime}$}$ ($0.27\hbox{$^{\prime\prime}$}$ at 2.4 $\mu$m) free atmosphere contribution. This would be significantly better than any other site studied to date, and, combined with the excellent atmospheric transmission at infrared wavelengths, the low scintillation index, and the possibility of performing long continuous observations, the potential scientific value of an appropriate observatory on the high antarctic plateau is undeniable. It is, of course, necessary to quantify the atmospheric seeing and transmission characteristics of sites such as Domes A and C, and such measurements are planned for the near future.

The vertical $C_{\rm N}^{2}$ profile at the South Pole is favourable for image restoration using an adaptive optics system that corrects for the effects of the boundary layer turbulence. At optical wavelengths, image resolution of 0.2$\hbox{$^{\prime\prime}$}$ FWHM should be attainable over an angle of 2$\hbox{$^\prime$}$ or more, which would provide excellent sky coverage even for reasonably bright reference sources. If this level of performance is found to be practically achievable, it may be that the South Pole itself would be a suitable observatory site, given the support infrastructure already in place at this location.

Acknowledgements

We wish to thank Al Harper, Bob Pernic and Bob Loewenstein from CARA (the University of Chicago), and John Storey, Michael Ashley and Michael Burton from the University of New South Wales, for their assistance. This research was supported in part by the U.S.A. National Science Foundation under a cooperative agreement with the Center for Astrophysical Research in Antarctica (CARA), grant number NSF OPP 89-20223. CARA is a National Science Foundation Science and Technology Center. Support from the Australian Department of Industry Science and Technology's Bilateral Program is gratefully acknowledged. Funding for all instrumentation was provided by l'Institut National des Sciences de l'Univers, France. We make special mention of the late Jean-François Manigault for his part in the successful completion of this research.