Dome C coherence time statistics from DIMM data

TL;DR

This study reanalyzes several years of DIMM data at Dome C, Antarctica, to measure atmospheric coherence time $ au_0$, revealing seasonal, height-dependent, and daytime variations crucial for adaptive optics.

Contribution

It provides the first daytime measurements of $ au_0$ at Dome C and analyzes seasonal and height-dependent behavior using extensive DIMM data.

Findings

Median $ au_0$ of 2.9ms at 8m height

Median $ au_0$ of 6ms at 20m during winter

Daytime $ au_0$ peaks at 5pm with values above 10ms

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 $\tau_0$. Statistics and seasonal behaviour of $\tau_0$ are given at two heights above the ground, 3m and 8m, for the wavelength $\lambda=500$nm. We found an annual median value of $2.9$ms 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 $\tau_0$ 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 $\tau_0$ 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.