1. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria I. Petenko 1,2, S. Argentini 1, G. Mastrantonio 1, A. Viola 1, M. Kallistratova 2, G. Casasanta 1, A. Conidi 1, R. Sozzi 3 1 Institute of Atmospheric Sciences and Climate, CNR, Via Fosso del Cavaliere 100, 00133, Roma, Italy. E-mail: i.petenko@isac.cnr.it 2 A.M.Obukhov Institute of Atmospheric Physics, RAS, Pyzhevskiy 3, 109117, Moscow, Russia 3 Regional Environmental Protection Agency of Lazio, Via Boncompagni 101, 00187 – Roma, Italy Spatio-temporal Pattern of the Surface-based Turbulent Layer during Polar Winter at Dome C, Antarctica as observed by Sodar

2.  1. Scientific motivations and objectives  2. Site and instrumentation  3. Occurrence and features of turbulent layers  4. Correlation between the depth of turbulent layers and meteorological parameters  5. Wavelike structures and their characteristics  6. Summary 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

3. S CIENTIFIC O BJECTIVES 1. Study the features of turbulence under extremely stable stratification observed during polar winter 2. Determine the correlation between the turbulence behaviour and meteorological conditions 3. Determine the wavelike structure features

4. We will see the features of atmospheric turbulence during the austral winter of 2012 in the interior of Antarctica French-Italian station of Concordia Dome C, Antarctica 75°S, 123°E, 3233 m a.s.l.

5. SODAR surface-layer high-resolution sodar measures a spatio-temporal structure of thermal turbulence beginning from ≈2 m up to 200 m with a vertical resolution <2 m, and a time resolution of 2 s. 1) Ultrasonic anemometer USA-1 by Metek 2) Net Radiometer CNR1 by Kipp & Zonen AWS Milos520 by Vaisaala Radiosonde RS92-SGPL 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria The experiment was held from December 2011 to December 2012 Description of the sodar and preliminary results: Argentini S., I. Petenko, et al. (2014) The surface layer observed by a high resolution sodar at Dome C, Antarctica. Annals of Geophysics, 56, 5; 10.4401/ag-6347. Frequency: 4850 Hz Pulse duration : 0.01 s Pulse repetition: 2 s

6. F EATURES OF THE P RESENTED R ESULTS “Quasi-LABORATORY” experiment – minimally influenced by external factors 1. Horizontal HOMOGENEITY - NO OROGRAPHY influence (flat surface with a slope < 0.1%) 2. NO external HEAT sources (almost no Sun) 3. (almost) NO DIURNAL VARIATIONS 4. Long-term measurements during several months – statistics is reliable 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

7. What does SODAR show? Sodar echograms show cross-section of the spatial and temporal pattern of thermal turbulence in height-time coordinates. The greyscale intensity (or conditional colours) is proportional to the Temperature Structure Parameter C T 2 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria S URFACE - BASED T URBULENT L AYER ( STL ) AS SHOWN BY SODAR The DEPTH of the STL is a HEIGHT of the top boundary

8. Variation of the STL Depth in Winter of 2012 Occurrence of Surface Turbulent Layer Depth: 0-10 m 33% 10-30 m 37% 30-50 m 17% > 50 m 13% 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

9. Surface-based Turbulent Layer occupies only the lowest 10-20% of a whole temperature inversion layer. This is the main difference between the turbulence in the long-lived stable boundary layer and the usual nocturnal inversion layer Depths of the Surface-based Turbulent Layer (from sodar) and of the Inversion Layer (from radiosonde) Heights of Surface Turbulent Layer and Inversion Layer averaged over Apr-Oct 2012 Heigth (m)Mean (m)Median (m)Std (m) Turbulent Layer 231620 Inversion Layer 13312563 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

10. M ETEOROLOGICAL C ONDITIONS FOR DIFFERENT STL D EPTHS “Shallow” STL, Depth 0-10 m, 836 hours – 33% “Deep” STL, Depth 30-50 m, 438 hours – 17%

11. The depth of the Surface-based Turbulent Layer increases with Wind Speed, and shows weak dependence on temperature STL Depth vs Wind Speed and Temperature 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Height 3.5 m Height 1.4 m

12. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Variation of STL vs Meteorological Parameters Shallow STL and Weak Turbulence Deep STL and Strong Turbulence Temperature Wind Speed & Direction

13. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria W AVELIKE P ATTERNS IN A NTARCTICA W AVELIKE PATTERNS ARE OFTEN OBSERVED IN THE INTERRIOR OF A NTARCTICA, FROM THE SURFACE TO THE UPPER ATMOSPHERIC LAYERS

14. Example of long-lived STL with WAVY internal structure (WAVE TRAINS) 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria V= 7 m/s S, T= -65°C Wavy braid parttern can be associated with gravity-shear waves due to the Kelvin-Helmholtz instability

15. Example of long-lived STL with UNIFORM internal structure 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria V= 5 m/s S, T= -65°C

16. Spectral Characteristics of Wave Trains High-Frequency part P2 is the period of waves Low-Frequency part P1 is the period of trains P1≈ 700 s P2 ≈ 20 s For the temperature gradient of 6.5°C/km measured by the radiosonde in the free atmosphere, buoyancy period ≈ 520 s

17. STL can be characterized by its DEPTH and INTERNAL STRUCTURE The observed STLs can be subdivided into several groups according to their depth and internal structure. “Shallow”: 1) Depth <20 m without any visible regularity of the internal structure. 2) Depth <20 m with a wavy internal sub-layer. “Deep”: 1) Depth of 20-60 m with uniform internal structure 2) Depth of 20-60 m with wavy internal structure of a braid form with periods of 60-300 s (Kelvin-Helmoholtz instability) 3) Depth of >60 m with wavy internal structure with periods of 60-120 s through the whole depth 4)* Depth of 30-60 m with periodical (of ≈10-12 minutes) alternation of wave trains (with internal periods of ≈20-30 s and duration of ≈4-5 minutes) and zones with uniform internal structure. * This case is more complicate and often occurs. C LASSIFICATION of STL 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

18. F EATURES OF T URBULENCE IN W INTER AT D OME C: In spite of 1)the absence of the Sun and very low temperatures, 2)extremely high static stability and strong temperature inversion extending up to 100-300 m with a strength reaching 30-40°C, 3)the absence of orography features 4)relatively long periods of steady weather conditions TURBULENCE is quite VIVID and LIVELY and shows different and variable spatio-temporal structures 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

19. Correlation between Seeing and STL Depth The best image quality (lowest seeing) is observed for lower STL depth Application for Astronomy The intensity of thermal turbulence measured by a sodar is characterized by the temperature structure parameter C T 2. The intensity of optically-active turbulence is described by the refraction index structure parameter C n 2. These parameters are connected directly C n 2 (h)= B(p, T) C T 2 (h) The coefficient B(p, T)= (79.2∙10 -6 pT -2 ) 2, where p is the air pressure in mb, T is the absolute temperature in K. The Turbulent Optical Factor (TOF) TOF = ∫C n 2 (h)dh evaluates a degree of degradation of a stellar image by turbulence localized in the layer at altitudes from h 1 to h 2. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Petenko, I. et al. (2014) Observations of optically active turbulence in the planetary boundary layer by sodar at the Concordia astronomical observatory, Dome C, Antarctica. Astronomy & Astrophys, A 568, A44 (2014) Correlation between Seeing and TOF The best image quality (lowest seeing) is observed for lower TOF values

20. Considerable thermal turbulence often occurs and extends up to several tens of metres forming the Surface-based Turbulent Layer (STL) at the Antarctic plateau during the austral winter. The STL occupies only the lowest 10-20% of the whole temperature-inversion layer. The STL depth increases with wind speed. Wind Speed seems to be the most relevant variable influencing the structure and intensity of thermal turbulence in the polar STL. Distinct wave activity within the STL occurs during a large part of the time and can be assumed to be the main feature of the STL occurring under very stable stratification. Classification of typical patterns of the spatio-temporal structure of turbulence observed by the use of the advanced high-resolution sodar is presented SUMMARY 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

21. Thank you Благодаря Merci Danke Gracias Grazie Спасибо 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

22. Example of long-lived STL with WAVY internal structure 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria V= 9 m/s S, T= -60°C

23. Example of long-lived STL with WAVY internal structure (WAVE TRAINS) 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria V= 6 m/s S, T= -65°C

24. Example of long-lived STL with WAVY internal structure (WAVE TRAINS) 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria V= 6 m/s S, T= -65°C

25. Meteorological conditions in winter of 2012 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria

26. W AVY S MOKE L AYER

27. Cross-section patterns of the Surface–based Turbulent Layer (STL) shown by sodar echograms Greyscale intensity is proportional to the strength of thermal turbulence characterised by the temperature structure parameter C T 2 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Typical profiles of C T 2 within STL

28. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Variation of STL vs Meteorological Parameters Low STL and Weak Turbulence

29. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Variation of STL vs Meteorological Parameters High STL and Strong Turbulence

30. 15th EMS, 07-11 Sept 2015, Sofia - Bulgaria Variation of STL vs Meteorological Parameters Variable STL and Strong Turbulence