Monitoring the optical turbulence in the surface layer at Dome C, Antarctica, with sonic anemometers

Abstract

The optical turbulence above Dome C in winter is mainly concentrated in the first tens of meters above the ground. Properties of this so-called surface layer (SL) were investigated during the period 2007-2012 by a set of sonics anemometers placed on a 45 m high tower. We present the results of this long-term monitoring of the refractive index structure constant C 2 n within the SL, and confirm its thickness of 35m. We give statistics of the contribution of the SL to the seeing and coherence time. We also investigate properties of large scale structure functions of the temperature and show evidence of a second inertial zone at kilometric spatial scales. *

Optical Sky Brightness and Transparency during the Winter Season at Dome A Antarctica from the Gattini-All-Sky Camera

“…Good average optical seeing above the boundary layer can be obtained at South Pole (i.e., 0 ′′ .37 in 17−27 m above the ground, Marks et al 1996) and Dome C (i.e., 0 ′′ .27, Lawrence et al 2004; 0 ′′ .36±0 ′′ .19 Agabi et al 2006;0 ′′ .36, Aristidi et al 2009;<0 ′′ .3, Giordano et al 2012, in ∼30 m above the ground. ; also see Vernin et al 2009;Aristidi et al 2015). So far the best seeing among all the ground-based astronomical sites was measured to be 0 ′′ .07 at Dome C (Lawrence et al 2004).…”

“…At Dome C, Lawrence et al (2004) found seeing of 0 27, while Agabi et al (2006) determined 0 36±0 19, Aristidi et al (2009) found 0 36, and Giordano et al (2012) found <0 3 at ∼30 m above the ground. See also Vernin et al (2009) and Aristidi et al (2015). Many astronomical observations could benefit from the consecutive periods of dark time at polar latitudes.…”

Dome C coherence time statistics from DIMM data

“…Fig. 15 of [4] shows that values of τ 0,s vary from 5-6ms in winter to 30ms in summer: this is also a factor 5. Also, the surface layer is rather thin and we have reported that a telescope placed at a height of 20m would be in the free atmosphere almost 50% of the time [2].…”

“…Long-term statistics of turbulence parameters as well as vertical profiles of turbulence were obtained. In particular, we pointed out the bimodal distribution of the seeing caused by a strong turbulent surface layer whose thickness was estimated to about 30m [1,2,3,4].…”

“…All these measurements were made at night time during the period 2004-2006. The coherence time in the surface layer (up to an altitude of 45m) was also measured during several years by a set of sonic anemometers placed on the 45m high US tower [4].…”