Observations of optically active turbulence in the planetary boundary layer by sodar at the Concordia astronomical observatory, Dome C, Antarctica

Abstract

Aims. An experiment was set up at the Concordia station in Antarctica during the winter-over period in 2012 to determine the behaviour of atmospheric optical turbulence in the lower part of the atmospheric boundary layer. The aim of the experiment was to study the influence of turbulence and weather conditions on the quality of astronomical observations. The Concordia station is characterised by the high quality of astronomical images thanks to very low seeing values. The surface layer in the interior of Antarctica during the winter is very stably stratified with the differences of temperature between the surface and the top of the inversion, which reach 20−35• C. In spite of this strong static stability, considerable thermal optically active turbulence sometimes occurs and extends to several tens of metres above the surface, depending on weather conditions. It is important to know the meteorological characteristics that favour good astronomical observations. Methods. The optical measurements of the seeing made by differential image motion monitors installed at two levels of 8 and 20 m were accompanied by observations of turbulence in the lowest one hundred meters. Turbulence was detected and evaluated using a high-resolution sodar developed specially for this purpose. The statistics of some relevant meteorological variables including the long-wave downward radiation, which indicates cloudiness, were determined. Results. Typical patterns of the vertical and temporal structure of turbulence shown by sodar echograms were identified, analysed, and classified. The statistics of the depth of the surface-based turbulent layer and the turbulent optical factor for different height layers are presented together with the seeing statistics. We analysed the dependence of both seeing and integral turbulence intensity within the first 100 m on temperature and wind speed. Conclusions. Seeing and turbulence intensity in the atmospheric boundary layer appear to be correlated. The best values of the seeing (<1 arcsec) are observed when the sodar shows very low turbulence intensity. The main contribution to the image distortion is due to turbulence generated within the lowest 30−50 m near the surface. The presented statistics of the vertical distribution of the atmospheric optical turbulence can be used to determine the optimal location for astronomical instruments.

Modeling the Dynamics of the Atmospheric Boundary Layer Over the Antarctic Plateau With a General Circulation Model

“…During the summer “night” (i.e., when the sun is close to the horizon), the nocturnal SBL is shallower than 50 m and an inertial low‐level jet develops (Gallée et al, ). During the polar night, the boundary layer is almost permanently stably stratified (Genthon et al, ) and the turbulent boundary layer, when present, is only a few meters or dozens of meters deep (Petenko et al, ; Pietroni et al, ). Dome C frequently experiences sudden “warming events,” when warm and moist air is advected from the coast over the Plateau resulting in a large anomaly of downward long wave radiative flux and in an abrupt warming of the low troposphere of several tens of Kelvin in a few hours (Gallée & Gorodetskaya, ; Genthon et al, ).…”

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

“…3b) was installed about 15 m from the sodar antennae. All data were quality controlled, and to remove outliers from the observations, a median absolute deviation filter (Barnett and Lewis 1984;Petenko et al 2014a) was applied to the measured time series.…”

“…New features of the surface-based turbulent layer were shown during the one-year experiment conducted at the Concordia station (Dome C, Antarctica) in 2012 (Petenko et al 2013(Petenko et al , 2014aArgentini et al 2014). A second long-term experiment using this sodar was made in 2014 at the same site investigating the diurnal behaviour of thermal turbulence in the ABL.…”

Stable boundary‐layer regimes at Dome C, Antarctica: observation and analysis

“…On the other hand, during the polar night in winter, quasi‐permanent stable stratification occurs, with extreme temperature gradients often greater than 1 K m −1 in the first metres above the ground (Genthon et al , 2013; Pietroni et al , 2014). The turbulent boundary‐layer height does not exceed a few tens of metres or even a few metres (Pietroni et al , 2012; Casasanta et al , 2014; Petenko et al , 2014).…”