Vertical Structure Of Turbulence Research Articles

Investigation of Turbulent Dissipation Rate Profiles from Two Radar Wind Profilers at Plateau and Plain Stations in the North China Plain

Turbulence is ubiquitous in the planetary boundary layer (PBL), which is of great importance to the prediction of weather and air quality. Nevertheless, the profiles of turbulence in the whole PBL as observed by radar wind profilers (RWPs) are rarely reported. In this communication, the purpose was to investigate the vertical structures of turbulence dissipation rate (ε) obtained from the Doppler spectrum width measurements from two RWPs at plateau (Zhangbei) and plain (Baoding) stations in the North China Plain for the year 2021, and to tease out the underlying mechanism for the difference of ε between Zhangbei and Baoding. Under clear-sky conditions, the annual mean value of ε in the PBL over the plateau station was found to be higher than that over the plain station throughout the daytime from 0900 to 1700 local standard time. The magnitude of ε at both stations showed significant seasonal variation, with the strongest ε in summer but the weakest in winter. If a larger difference between the 2 m air temperature and surface temperature (Ta−Ts), as a surrogate of sensible heat flux, is observed, the turbulence intensity tends to become stronger. The influence of vertical wind shear on turbulence was also analyzed. Comparison analyses showed that the plateau station of Zhangbei was characterized by larger sensible heat flux and stronger wind shear compared with the plain station of Baoding. This may account for the more intense ε within the PBL of Zhangbei. Moreover, the magnitude of ε in the PBL was positively correlated with the values of both Ta−Ts and vertical wind shear. The findings highlight the urgent need to characterize the vertical turbulence structure in the PBL over a variety of surfaces in China.

Two saturated states of the vertical shear instability in protoplanetary disks with vertically varying cooling times

Abstract Turbulence in protoplanetary disks plays an important role in dust evolution and planetesimal formation. The vertical shear instability (VSI) is one of the candidate hydrodynamic mechanisms that can generate turbulence in the outer disk regions. The VSI requires rapid gas cooling in addition to vertical shear. A linear stability analysis suggests that the VSI may not operate around the midplane where gas cooling is inefficient. In this study, we investigate the nonlinear outcome of the VSI in disks with a linearly VSI-stable midplane region. We perform two-dimensional global hydrodynamical simulations of an axisymmetric disk with vertically varying cooling times. The vertical cooling time profile determines the thicknesses of the linearly VSI-stable midplane layer and unstable layers above and below the midplane. We find that the thickness of the midplane stable layer determines the vertical structure of VSI-driven turbulence in the nonlinear saturated state. We identify two types of final saturated state: (i) T states, characterized by vertical turbulent motion penetrating into the VSI-stable midplane layer, and (ii) pT states, characterized by turbulent motion confined in the unstable layers. The pT states are realized when the midplane VSI-stable layer is thicker than two gas scale heights. We also find that the VSI-driven turbulence is largely suppressed at all heights when the VSI-unstable region lying above and below the midplane is thinner than two gas scale heights. We present empirical formulas that predict the strength of VSI-driven turbulence as a function of the thicknesses of the unstable and stable layers. These formulas will be useful for studying how VSI-driven turbulence and dust grains controlling the disk cooling efficiency evolve simultaneously.

Atmospheric turbulence characteristics in the troposphere and lower stratosphere of core monsoon zone

The geographical location of Central India (CI) is often under the influence of a variety of weather phenomena, viz., the Indian Summer Monsoon (ISM) and its associated low-pressure systems, heat waves, cold waves, and western disturbances. The present study investigates the Vertical Structure of atmospheric Turbulence (VST) in terms of the refractive index structure parameter (Cn2), in the troposphere and lower stratosphere over the core monsoon zone in the CI. Ten years (2011−2020) of GPS-radiosonde (GPS-RS) measurements and reanalysis datasets are employed to bring out the turbulence characteristics over the study region. The strong turbulence values below 12 km during the monsoon season are due to the frequent convective instabilities and higher vertical velocities, whereas contrasting VST is noted during non-monsoon seasons with significant turbulence intensities reaching up to the upper levels. The frequent convective instabilities and updrafts make the monsoon season's VST more homogeneous isotropic turbulence in character. Observed seasonal variability in VST is attributed mainly to moisture availability, thermal structure, presence of tri-model clouds, and a flip-flop pattern of mid-tropospheric wind circulation conditions. The early signature of the ISM onset with the higher cold cloud fraction is responsible for the observed weak turbulence zone centered at 14 km altitude. This striking weak Cn2 < 10−17 m−2/3 over the monsoon core zone VST is one of the most intriguing features observed in the present study. The signatures of various weather conditions such as heat waves, depressions, and cold waves are reflected in the observed variations of the VST during summer, monsoon, and winter, respectively. The variations in the pre/post VST and during specific weather events are attributed to the remarkable difference in relative humidity and temperature conditions. The present results provide a quantitative assessment of VST, including its seasonal evolution over Bhopal, using GPS-RS observations for the first time. The impact of better temporal/height sampling of GPS-RS data is evidenced by implementing the Thorpe method to estimate the outer scale of turbulence. The present analysis will also assist in designing experimental specifications for the proposed wind profiler in CI's Atmospheric Research Testbed for all-weather scale applications.

The vertical turbulent structure within the surface boundary layer above a Vineyard in California’s Central Valley during GRAPEX

The vertical turbulent structure within the surface boundary layer above a Vineyard in California’s Central Valley during GRAPEX

Vertical turbulent exchange structure and parametrization for 3D shallow water hydrodynamics models

The work describes research of vertical turbulent exchange structure and parametrization for 3D shallow water hydrodynamics models. In this paper, the coefficients of horizontal turbulent exchange are calculated using a whole set of averaging periods of turbulent velocity pulsations. Using experimental data on the pulsations of the velocity components, the coefficient of vertical turbulent exchange was calculated on the basis of various approaches to its parameterization, based on the analysis of the obtained coefficient distributions, the most adequate parameterization of the coefficient was selected, which is used in the software package. The distribution of the vertical turbulent exchange coefficient obtained in a numerical experiment was compared with the results of full-scale measurements, and the calculation results obtained using the mathematical statistics apparatus were analysed.

Modeled Three‐Dimensional Currents and Eddies on an Alongshore‐Variable Barred Beach

AbstractCirculation in the nearshore region, which is critical for material transport along the coast and between the surf zone and the inner shelf, includes strong vortical motions. The horizontal length scales and vertical structure associated with vortical motions are not well documented on alongshore‐variable beaches. Here, a three‐dimensional phase‐resolving numerical model, Simulating WAves till SHore (SWASH), is compared with surfzone waves and flows on a barred beach, and is used to investigate surfzone eddies. Model simulations with measured bathymetry reproduce trends in the mean surfzone circulation patterns, including alongshore currents and rip current circulation cells observed for offshore wave heights from 0.5 to 2.0 m and incident wave directions from 0 to 15° relative to shore normal. The length scales of simulated eddies, quantified using the alongshore wavenumber spectra of vertical vorticity, suggest that increasing wave directional spread intensifies small‐scale eddies ((10) m). Simulations with bathymetric variability ranging from alongshore uniform to highly alongshore variable indicate that large‐scale eddies ((100) m) may be enhanced by surfzone bathymetric variability, whereas small‐scale eddies ((10) m) are less dependent on bathymetric variability. The simulated vertical dependence of the magnitude and mean length scale (centroid) of the alongshore wavenumber spectra of vertical vorticity and very low‐frequency (f ≈ 0.005 Hz) currents is weak in the outer surf zone, and decreases toward the shoreline. The vertical dependence in the simulations may be affected by the vertical structure of turbulence, mean shear, and bottom boundary layer dynamics.

Effects of Vegetation and Topography on the Boundary Layer Structure above the Amazon Forest

AbstractObservational data from two field campaigns in the Amazon forest were used to study the vertical structure of turbulence above the forest. The analysis was performed using the reduced turbulent kinetic energy (TKE) budget and its associated two-dimensional phase space. Results revealed the existence of two regions within the roughness sublayer in which the TKE budget cannot be explained by the canonical flat-terrain TKE budgets in the canopy roughness sublayer or in the lower portion of the convective ABL. Data analysis also suggested that deviations from horizontal homogeneity have a large contribution to the TKE budget. Results from LES of a model canopy over idealized topography presented similar features, leading to the conclusion that flow distortions caused by topography are responsible for the observed features in the TKE budget. These results support the conclusion that the boundary layer above the Amazon forest is strongly impacted by the gentle topography underneath.

Variations in Ocean Mixing from Seconds to Years.

Over the past several decades, there has developed a community-wide appreciation for the importance of mixing at the smallest scales to geophysical fluid dynamics on all scales. This appreciation has spawned greater participation in the investigation of ocean mixing and new ways to measure it. These are welcome developments given the tremendous separation in scales between the basins, [Formula: see text]) m, and the turbulence, [Formula: see text]) m, and the fact that turbulence that leads to thermodynamically irreversible mixing in high-Reynolds-number geophysical flows varies by at least eight orders of magnitude in both space and time. In many cases, it is difficult to separate the dependencies because measurements are sparse, also in both space and time. Comprehensive shipboard turbulence profiling experiments supplemented by Doppler sonar current measurements provide detailed observations of the evolution of the vertical structure of upper-ocean turbulence on timescales of minutes to weeks. Recent technical developments now permit measurements of turbulence in the ocean, at least at a few locations, for extended periods. This review summarizes recent and classic results in the context of our expanding knowledge of the temporal variability of ocean mixing, beginning with a discussion of the timescales of the turbulence itself (seconds to minutes) and how turbulence-enhanced mixing varies over hours, days, tidal cycles, monsoons, seasons, and El Niño-Southern Oscillation timescales (years).

Statistics of the Optical Turbulence from the Micrometeorological Measurements at the Baykal Astrophysical Observatory Site

The paper focuses on the investigations of the optical turbulence structure. The distributions of the repeatability of the structure characteristic of the air refractive index are obtained. A scenario of decreasing the intensity of the optical turbulence in the summer is discussed. Numerical estimates of this scenario are given. Using classical methods of wavefront analysis, the results of the first studies of the vertical structure of atmospheric turbulence at the Baykal astrophysical observatory site are presented.

Comparison of the turbulence structure during light and heavy haze pollution episodes

To obtain the differences in the turbulence structures between the light and heavy haze pollution process, a light pollution episode (LPE) from November 3 to 72,017, and a heavy pollution episode (HPE) from December 15 to 232,016, were investigated. The weather conditions, mean meteorological fields, and turbulence structures of the two episodes were analysed. The results show that the two cases have similar weather backgrounds, and the differences in mean meteorological field are mainly related to the difference in the degree of solar radiation weakening. The turbulence during the HPE was suppressed to a greater extent in both thermal and dynamic effects. The structure of turbulence is weak and typically characterized by intermittent turbulence in the stable boundary layer. The parameter IS (Intermittent Strength) is introduced to indicate the strength of intermittency. Because of the complexity of atmospheric motion, we use the change in IS, i.e., ∆IS, to indicate the change in the intensity of turbulent intermittency during each pollution process. In the accumulation stage, the weakening of turbulent exchange caused by the influence of sub-mesoscale motion may result in poor turbulent diffusion conditions, which should be considered because they can lead to heavy pollution events when ∆IS > 0.1. The same conclusions were verified in an analysis of Tianjin for these two cases. Further analysis of the vertical structure of turbulence indicated that during the pollution stage of the LPE, the turbulent energy comes from the surface and is consistent with the traditional surface layer turbulent transport mechanism. Moreover, the upper layer intermittent strength is stronger than that in the lower layer, and ∆IS < 0.1 at different heights. During the pollution stage of the HPE, the boundary layer is almost decoupled from the surface, and ∆IS > 0.1 in all layers, which suggests that the weakening of turbulent exchange affected the vertical turbulence structure and resulted in pollutant accumulation. During the dissipation stage of both the HPE and the LPE, the low-level jets provide a turbulence source in the upper layer. The effect of sub-mesoscale motion is weak, and the turbulence component diffuses pollutants. In this stage, ∆IS < 0.1 in all layers. The upside-down structure of the atmospheric boundary layer leads to full coupling with the ground and promotes the dissipation of pollutants during the HPE. And, the analysis of the pollution processes, from December 16, 2016 to January 8, 2017, also indicate that ∆IS > 0.1 is a feature of severe pollution. The results for these cases indicate that ∆IS = 0.1 can be used as an indicator to characterize the turbulent exchange conditions and different levels of contamination.

A joint velocity-intermittency analysis reveals similarity in the vertical structure of atmospheric and hydrospheric canopy turbulence

Turbulent flow through and over vegetation continues to draw significant research attention given its relevance to a plethora of applications in earth and environmental science. Canopy flows are characterized by three-dimensional coherent vortical motions not directly accessible from single-point measurements, which pose a challenge to formalizing links between vegetation structure and turbulent motion. A joint velocity-intermittency technique is applied to velocity data collected within and above aquatic vegetation in a hydraulic flume and above a forested canopy. The approach reveals behavior that provides greater insight into canopy flow dynamics than may be inferred from the vertical profiles of mean velocity, turbulence intensity and Reynolds stresses, which are the quantities usually studied. There is a remarkable similarity in the structure of such flows between the forest canopy and the flume study despite large differences in morphology and stem rigidity. In particular, these results determine an outer flow type arising above 1.5 canopy heights, while turbulent in-rushing events are most significant at the zero-plane displacement. The approach also implies ways in which improved models for canopy turbulence may be developed.

Intermittent turbulence contributes to vertical dispersion of PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; in the North China Plain: cases from Tianjin

Abstract. Heavy particulate pollution events have frequently occurred in the North China Plain over the past decades. Due to high emissions and poor dispersion conditions, issues are becoming increasingly serious during cold seasons. Although early studies have explored some potential reasons for air pollution, there are few works focusing on the effects of intermittent turbulence. This paper draws upon two typical PM2.5 (particulate matter with diameter less than 2.5 mm) pollution cases from the winter of 2016–2017. After several days of gradual accumulation, the concentration of PM2.5 near the surface reached the maximum as a combined result of strong inversion layer, stagnant wind, and high ambient humidity and then sharply decreased to a very low level within a few hours. In order to identify the strength of turbulent intermittency, an effective index, called the intermittency factor (IF), was proposed by this work. The results show that the turbulence is very weak during the cumulative stage due to the suppression by strongly stratified layers, while for the stage of dispersion, the turbulence is highly intermittent and not locally generated. The vertical structure of turbulence and wind profiles confirms the generation and downward transport of intermittent turbulence associated with low-level jets. The intermittent turbulent fluxes contribute positively to the vertical transport of particulate matter and improve the air quality near the surface. This work has demonstrated a possible mechanism of how intermittent turbulence affects the dispersion of particulate matter.

Turbulence from Breaking Surface Waves at a River Mouth

AbstractObservations of surface waves, currents, and turbulence at the Columbia River mouth are used to investigate the source and vertical structure of turbulence in the surface boundary layer. Turbulent velocity data collected on board freely drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys are corrected for platform motions to estimate turbulent kinetic energy (TKE) and TKE dissipation rates. Both of these quantities are correlated with wave steepness, which has previously been shown to determine wave breaking within the same dataset. Estimates of the turbulent length scale increase linearly with distance from the free surface, and roughness lengths estimated from velocity statistics scale with significant wave height. The vertical decay of turbulence is consistent with a balance between vertical diffusion and dissipation. Below a critical depth, a power-law scaling commonly applied in the literature works well to fit the data. Above this depth, an exponential scaling fits the data well. These results, which are in a surface-following reference frame, are reconciled with results from the literature in a fixed reference frame. A mapping between free-surface and mean-surface reference coordinates suggests 30% of the TKE is dissipated above the mean sea surface.

ANÁLISE DA ESTRUTURA VERTICAL DO BALANÇO DE ENERGIA CINÉTICA TURBULENTA DURANTE A OCORRÊNCIA DE EVENTOS DE INTERMITÊNCIA GLOBAL

This study aims to analyze the vertical structure of the terms of the ECT balance equation for the occurrence of intermittent events generated in surface and propagate upward. In order to verify that the dominant terms and the role of each term during such events. It was used FLOSSII experimental data collected in seven vertical levels (1 m, 2 m, 5 m, 10 m, 15 m, 20 m and 30 m) and have a sampling frequency of 60 Hz. The study period comprises between 20 November 2002 to 02 April 2003 and of that total, this study, we analyzed 108 nights. The majority of events generated surface (EB) are very weak compared to the events generated at the top of the tower layer and propagate down. The analyzes made by vertical turbulence structure and ECT balance for the EB’s showed that the dominant term near surface is the mechanical production. Thus, with increasing shear surface, producing turbulence and consequently, the transport of works term “loading” turbulence to higher levels of the atmosphere.

Exploring Vertical Turbulence Structure in Neutrally and Stably Stratified Flows Using the Weather Research and Forecasting–Large-Eddy Simulation (WRF–LES) Model

Following Sun et al. (J Atmos Sci 69(1):338–351, 2012), vertical variations of turbulent mixing in stably stratified and neutral environments as functions of wind speed are investigated using the large-eddy simulation capability in the Weather Research and Forecasting model. The simulations with a surface cooling rate for the stable boundary layer (SBL) and a range of geostrophic winds for both stable and neutral boundary layers are compared with observations from the Cooperative Atmosphere–Surface Exchange Study 1999 (CASES-99). To avoid the uncertainty of the subgrid scheme, the investigation focuses on the vertical domain when the ratio between the subgrid and the resolved turbulence is small. The results qualitatively capture the observed dependence of turbulence intensity on wind speed under neutral conditions; however, its vertical variation is affected by the damping layer used in absorbing undesirable numerical waves at the top of the domain as a result of relatively large neutral turbulent eddies. The simulated SBL fails to capture the observed temperature variance with wind speed and the observed transition from the SBL to the near-neutral atmosphere with increasing wind speed, although the vertical temperature profile of the simulated SBL resembles the observed profile. The study suggests that molecular thermal conduction responsible for the thermal coupling between the surface and atmosphere cannot be parameterized through the Monin–Obukhov bulk relation for turbulent heat transfer by applying the surface radiation temperature, as is common practice when modelling air–surface interactions.

Dynamics of stratified turbulence decaying from a high buoyancy Reynolds number

We present direct numerical simulations (DNS) of unforced stratified turbulence with the objective of testing the strongly stratified turbulence theory. According to this theory the characteristic vertical scale of the turbulence is given by $\ell _{v}\sim u_{h}/N$, where $u_{h}$ is the horizontal velocity scale and $N$ the Brunt–Väisälä frequency. Combined with the hypothesis of the energy dissipation rate scaling as ${\it\epsilon}\sim u_{h}^{3}/\ell _{h}$, this theory predicts inertial range scalings for the horizontal spectrum of horizontal kinetic energy and of potential energy, according to $E(k_{h})\propto k_{h}^{-5/3}$. We begin by presenting a scaling analysis of the horizontal vorticity equation from which we recover the result regarding the vertical scale, $\ell _{v}\sim u_{h}/N$, highlighting in the process the important dynamical role of large-scale vertical shear of horizontal velocity. We then present the results from decaying DNS, which show a good agreement with aspects of the theory. In particular, the vertical Froude number is found to reach a constant plateau in time, of the form $Fr_{v}=u_{h}/(N\ell _{v})=C$ with $C=O(1)$ in all the runs. The derivation of the dissipation scaling ${\it\epsilon}\sim u_{h}^{3}/\ell _{h}$ at low Reynolds number in the context of decaying stratified turbulence highlights that the same scaling holds at high $\mathscr{R}=ReFr_{h}^{2}\gg 1$ as well as at low $\mathscr{R}\ll 1$, which is known (see Brethouwer et al., J. Fluid Mech., vol. 585, 2007, pp. 343–368) but not sufficiently emphasized in recent literature. We find evidence in our DNS of the dissipation scaling holding at $\mathscr{R}=O(1)$, which we interpret as being in the viscous regime. We also find ${\it\epsilon}_{k}\sim u_{h}^{3}/\ell _{h}$ and ${\it\epsilon}_{p}\sim u_{h}^{3}/\ell _{h}$ (with ${\it\epsilon}={\it\epsilon}_{k}+{\it\epsilon}_{p}$), in our high-resolution run at earlier times corresponding to $\mathscr{R}=O(10)$, which is in the transition between the strongly stratified and the viscous regimes. The horizontal spectrum of horizontal kinetic energy collapses in time using the scaling $E_{h}(k_{h})=C_{1}{\it\epsilon}_{k}^{2/3}k_{h}^{-5/3}$ and the horizontal potential energy spectrum is well described by $E_{p}(k_{h})=C_{2}{\it\epsilon}_{p}{\it\epsilon}_{k}^{-1/3}k_{h}^{-5/3}$. The presence of an inertial range in the horizontal direction is confirmed by the constancy of the energy flux spectrum over narrow ranges of $k_{h}$. However, the vertical energy spectrum is found to differ significantly from the expected $E_{h}(k_{v})\sim N^{2}k_{v}^{-3}$ scaling, showing that $Fr_{v}$ is not of order unity on a scale-by-scale basis, thus providing motivation for further investigation of the vertical structure of stratified turbulence.

Observations of turbulence within the surf and swash zone of a field-scale sandy laboratory beach

Current coastal-evolution models generally lack the ability to accurately predict bed level change in shallow (<~2m) water, which is, at least partly, due to the preclusion of the effect of surface-induced turbulence on sand suspension and transport. As a first step to remedy this situation, we investigated the vertical structure of turbulence in the surf and swash zone using measurements collected under random shoaling and plunging waves on a steep (initially 1:15) field-scale sandy laboratory beach. Seaward of the swash zone, turbulence was measured with a vertical array of three Acoustic Doppler Velocimeters (ADVs), while in the swash zone two vertically spaced acoustic doppler velocimeter profilers (Vectrino profilers) were applied. The vertical turbulence structure evolves from bottom-dominated to approximately vertically uniform with an increase in the fraction of breaking waves to ~50%. In the swash zone, the turbulence is predominantly bottom-induced during the backwash and shows a homogeneous turbulence profile during uprush. We further find that the instantaneous turbulence kinetic energy is phase-coupled with the short-wave orbital motion under the plunging breakers, with higher levels shortly after the reversal from offshore to onshore motion (i.e. wavefront).

Vertical structure of turbulence within a depression surrounded by coral reef colonies

Turbulence is important in coral reefs but is difficult to measure in the field. In this paper, I present in situ measurements of waves, currents, and turbulence to study the vertical structure of turbulence within a depression (curved channel) that is surrounded by coral reef colonies on a fringing reef in Hobihu, Nan-Wan Bay, southern Taiwan. Turbulence was measured using a dual-velocimetry technique, and wave bias contamination in the turbulence is controlled using ogive curve testing of the turbulent shear stress (TSS). The observed turbulent dissipation rate (e) is approximately five times greater than simultaneous observations over the nearby sandy bottom site, which indicates stronger mixing within the coral reef than on sandy bottoms. The low ratio of the TSS to the turbulent kinetic energy (TKE) and sweeping events indicate that energetic momentum is transported downward into the depression of the coral reef canopies. The observed value of e exceeds the shear production rate, which suggests that transport terms or other source terms might be important. Direct evaluation of the transport terms suggests that vertical turbulent transport and advection are significant mechanisms that diffuse and convect the TKE downward into the depression. The observed TSS can be described well by the Prandtl–von Karman eddy viscosity model and a two-equation turbulence model, which suggests that it is possible to develop a physically based model to quantify nutrient uptake and mass transfer in coral reefs under complex wave–current coastal flows.

Sediment dynamics on a steep, megatidal, mixed sand–gravel–cobble beach

Abstract. Results are presented from a pilot study of shore-face sediment dynamics on a steep, poorly sorted, coarse-grained, megatidal beach at the head of the Bay of Fundy, Nova Scotia, Canada. The experiment involved the first field deployment of a prototype wideband, pulse-coherent, bistatic acoustic Doppler profiling system. Measurements of the vertical structure of flow and turbulence above a sloping bed, as well as bed material velocity, demonstrate the capabilities of this instrument vis-à-vis studies of nearshore sediment dynamics at the field scale. The second focus of the paper is the unexpected observation that the surficial sediment median diameter, across the lower two-thirds of the intertidal zone, underwent a pronounced decrease when wave forcing was more energetic, compared to values observed during calmer conditions. The explanation for this result appears to involve the formation – in wave-dominated conditions – of metre-scale wavelength, 20 cm high ripples on the rising tide, which are then planed flat by the swash and/or the shore break on the subsequent ebb.

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

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.