Stable Surface-Based Turbulent Layer During the Polar Winter at Dome C, Antarctica: Sodar and In Situ Observations

An experiment to investigate atmospheric turbulence was performed at Concordia station (Dome C, Antarctica) during winter 2012, finding significant turbulence in a near-surface layer extending to heights of a few tens of metres, despite the strong stable stratification. The spatial and temporal behaviour of thermal turbulence is examined using a high-resolution sodar, starting from the lowest few metres with a vertical resolution better than 2 m. Sodar observations are complemented by in situ measurements using a weather station and radiometers near the surface, temperature and wind-speed sensors at six levels on a 45-m tower, and radiosondes. The depth of the surface-based turbulent layer (SBTL) at Dome C during the whole winter is directly measured experimentally for the first time, and has an average depth of ≈ 23 m, varying from a few to several tens of metres, while the inversion-layer depth ≈ 380 m. Relationships between the depth of the SBTL and atmospheric parameters such as the temperature, wind speed, longwave radiation, Brunt–Väisälä frequency and Richardson number are shown. The SBTL under steady weather conditions is analyzed and classified into three prevailing types: (i) a very shallow layer with a depth < 15 m, (ii) a shallow layer of depth 15–70 m with uniform internal structure, (iii) a shallow layer of depth 20–70 m with waves. Wave activity in the SBTL is observed during a significant portion of the time, with sometimes regular (with periodicity of 8–15 min) trains of Kelvin–Helmholtz billow-like waves occurring at periods of 20–60 s, and lasting several hours.