Dome C coherence time statistics from DIMM data

Abstract

We present a reanalysis of several years of DIMM data at the site of Dome C, Antarctica, to provide measurements of the coherence time τ 0 .Statistics and seasonal behaviour of τ 0 are given at two heights above the ground, 3m and 8m, for the wavelength λ = 500nm. We found an annual median value of 2.9ms at the height of 8m. A few measurements could also be obtained at the height of 20m and give a median value of 6ms during the period June-September. For the first time, we provide measurements of τ 0 in daytime during the summer, which appears to show the same time dependence as the seeing with a sharp maximum at 5pm local time. Exceptional values of τ 0 above 10ms are met at this particular moment. The continuous slow variations of turbulence conditions during the day offers a natural test bed for a solar adaptive optics system.