Dome C site testing: surface layer, free atmosphere seeing and isoplanatic angle statistics

TL;DR

This study analyzes 3.5 years of site testing data at Dome C, Antarctica, revealing detailed statistics of atmospheric turbulence, surface layer properties, and free atmosphere seeing, confirming Dome C's exceptional astronomical observing conditions.

Contribution

It provides a comprehensive statistical characterization of the surface and free atmosphere turbulence at Dome C using multi-elevation DIMM measurements, including surface layer height and turbulence contribution.

Findings

Surface layer is very sharp, less than 1 m thick.

Median free atmosphere seeing is 0.36 arcsec.

Surface layer accounts for 95% of turbulence outside summer.

Abstract

This paper analyses 3.5 years of site testing data obtained at Dome C, Antarctica, based on measurements obtained with three DIMMs located at three different elevations. Basic statistics of the seeing and the isoplanatic angle are given, as well as the characteristic time of temporal fluctuations of these two parameters, which we found to around 30 minutes at 8 m. The 3 DIMMs are exploited as a profiler of the surface layer, and provide a robust estimation of its statistical properties. It appears to have a very sharp upper limit (less than 1 m). The fraction of time spent by each telescope above the top of the surface layer permits us to deduce a median height of between 23 m and 27 m. The comparison of the different data sets led us to infer the statistical properties of the free atmosphere seeing, with a median value of 0.36 arcsec. The C_n^2 profile inside the surface layer is also deduced from the seeing data obtained during the fraction of time spent by the 3 telescopes inside this turbulence. Statistically, the surface layer, except during the 3-month summer season, contributes to 95 percent of the total turbulence from the surface level, thus confirming the exceptional quality of the site above it.