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Optical Turbulence in Meso-NH: study of a site with extremely stable conditions (Dome C, Antarctica) Lascaux Franck Masciadri Elena, Hagelin Susanna INAF – Osservatorio Astrofisico di Arcetri, Florence, Italy

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-Grid-nested simulation: Δx=1 km in the innermost domain. -Low horizontal resolution monomodel simulation: Δx=100 km. Domain 1: Δx=25 km 3000 km 400 km 80 km Domain 2: Δx=5 km Domain 3: Δx=1 km Zoom over Dome C Area C A F PS C (3205 m) 6000 km C PS A C C (3230 m) MESO-NH CONFIGURATIONS (1) More details in Lascaux et al. (SPIE 2008) GTOPO30 GTOPO30 not accurate over Antarctica => Use of RAMPDEM version 2* *Liu, H et al., “Radarsat Antarctic Mapping Project Digital Elevation Model version 2”. Boulder, CO; National Snow and Ice Data Center. Digital media. 3250m 3220m

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-Grid-nested simulation: Δx=1 km in the innermost domain. Domain 1: Δx=25 km 3000 km 400 km 80 km Domain 2: Δx=5 km Domain 3: Δx=1 km; t=3 s C PS A C C (3230 m) MESO-NH CONFIGURATIONS (2) -Calibration (see last slides) made with this configuration (in grid-nesting mode only). + MASDEV 4.7 bug 4 + SURFEX 4.7 with -LPHYSDOMEC=T (physics adapted to Dome C) -LDEEPSOIL=T (force surface temperature towards a climatological value) RAMPDEMv2 -Vertical grid: 1st point at 2 m, 12 points in 100 m, and H=600 m above 3.5 km (ok for Dome C, flat orography) 3200m 3230m

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SIMULATED VERTICAL PROFILES ABOVE DOME C Meteorological parameters (Lascaux et al., 2009) H (M) H (KM) H (KM) (K) RS ANA MM GN H (KM) (m/s)H (KM) H (M) RS ANA MM GN TEMPERATURE WIND SPEED Mean vertical profiles of temperature and wind speed above Dome C for 47 winter nights. RS = radiosoundings ; ANA = ECMWF Analyses ; MM = Meso-NH monomodel simulation ; GN = Meso-NH grid-nested simulation.

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Optical Turbulence – Meso-NH V (wind intensity) + P (pressure) + T (temperature) + Lo (dynamical outer scale) From the C n 2 field we can deduce all the astroclimatic parameters that depend on it. -Especially the seeing: Refractive index structure parameter Best possible angular resolution, in arcsec (“) With λ =0, m -But also the surface layer thickness (H sl ), with the criteria used in Trinquet et al (15 winter nights observed): SL (Surface Layer) FA (Free Atmosphere) H sl Ground

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TEMPORAL EVOLUTION OF Cn² PROFILES -15 nights between 21 June 2005 and 21 September 2005 (winter) have been observed by Trinquet et al. (2008). We simulated these nights using the astro-meso-nh package developed by the team. - Examples of simulations for 3 nights: monomodel (left) and grid-nested (right) Taken from Lascaux et al H sl = 25.3 m H sl = 38.2 m H sl = 18.2 m

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MEDIAN Cn² VERTICAL PROFILE Medians of the simulated mean vertical profile of Cn² (between 12 UT and 17 UT) for the 15 nights observed in Trinquet et al. (2008), above Dome C. ε obs,FA = 0,3” ε mnh,FA = 0,45” H sl,obs = 35,3m H sl,mnh = 48,5m AVERAGE MEDIAN ε obs,TOT = 1,6” ε mnh,TOT = 3,1”

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CORRELATION PLOTS Observed J Simulated J Observed J Total JSurface Layer JFree Atmosphere J J = C n 2 (h).dh ε obs,FA = 0,3” ε mnh,FA = 0,45” H sl,obs = 35,3m H sl,mnh = 48,5m AVERAGE H sl MEDIAN ε ε obs,TOT = 1,6” ε mnh,TOT = 3,1”

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CALIBRATION AT DOME C USING OBSERVATIONS Goal: -to adjust the total intensity of the optical turbulence, especially inside the surface layer where it is too strong. Method : -first step: modification of a coefficient in the Meso-NH turbulence scheme. For this, we change XCTP in ini_cturb.f90: from 4 to 4.88 (computed from the ratio between observed and simulated H sl ) -> Change of XCSHF coefficient in the w’ v ’ term. => H sl and ε -second step: correction in the optical turbulence package in the C T 2 computations, from which is deduced the C n 2. From C T 2 as x 3 x LM 4/3 x ( / Z) 2 to C T 2 as x 3 x LM 4/3 x ( / Z) 2 (deduced from the ratio between observed and simulated median J= C n 2.dh) => ~H sl and ε -third step: correction of the TKE min, in order to have a model more active in altitude. No impact near the surface. TKE min (new) = TKE min (old) x 1.74

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AFTER CALIBRATION Potential temperature profiles, some examples: Radiosoundings ECMWF analyses M-NH before calibration M-NH after calibration Average (only 8 days) 0 m 150 m AGL

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AFTER CALIBRATION Simulations of the same sample of nights. Configuration 2. Median vertical C n 2 profiles: Observations M-NH, before calibration M-NH, after complete calibration

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AFTER CALIBRATION Seeing and surface layer thickness correlation plots: M-NH, before calibration M-NH, after complete calibration Total Seeing Free Atmosphere Seeing Surface Layer Thickness ε tot,before = 2.90” ε FA,before = 0.45” H sl,before = 44.4 m ε tot, after = 1.70” ε FA,after = 0.30” H sl,after = 44.2 m ε tot, OBS = 1.6” ε FA,OBS = 0.3” H sl,OBS = 36.4 m

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CONCLUSIONS Acknowledgements: This work has been funded by the Marie Curie Excellence Grant (FOROT) – MEXT-CT Data set from the MARS Catalog (ECMWF) are used in this presentation. Access to the MARS Catalog is authorized by the Servizio Meteorologico dell’Aeronautica Militare Italiana. -We presented here a detailed study of the wintertime optical turbulence at Dome C, Antarctica, with Meso-NH in which our team included an astronomical package allowing for the forecasting of optical turbulence (the astro-meso-nh package, only available at the Osservatorio Astrofisico di Arcetri). -Configuration used: o Masdev 4.7 bug 4 + Surfex LDOMEC=T + LDEEPSOIL=T o Use of the “Radarsat Antarctic Mapping Project Digital Elevation Model version 2” for the description of the orography (GTOPO30 unreliable in the Plateau). o X = 25, 5, and 1 km. o Vertical grid: first point at 2 m, 12 points in the first 100 m, 55 levels up to 22 km.

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CONCLUSIONS Acknowledgements: This work has been funded by the Marie Curie Excellence Grant (FOROT) – MEXT-CT Data set from the MARS Catalog (ECMWF) are used in this presentation. Access to the MARS Catalog is authorized by the Servizio Meteorologico dell’Aeronautica Militare Italiana. -Optical Turbulence results: o Before calibration with available observations, winter simulations with the astro- mnh package generate too much optical turbulence and a slightly too high surface layer thickness. o After a calibration process (adaption of surface fluxes, C T 2 coefficient, and modification of TKE min ), results are more satisfying. ε tot,before = 2.90” ε FA,before = 0.45” H sl,before = 44.4 m ε tot, after = 1.70” ε FA,after = 0.30” H sl,after = 44.2 m ε tot, OBS = 1.6” ε FA,OBS = 0.3” H sl,OBS = 36.4 m o Next step: looking at other sites in Antarctica (Dome A, South Pole...)

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AFTER CALIBRATION Simulations of the same sample of nights. Some examples of C n 2 profiles: Zoom up to 50m Fisrt 300 m 04/07/200507/09/200521/09/2005 Reference simulations Simulations using calibration 04/07: Hsl from 31.3m to 30.4m ε tot from 4.05” to 2.28” ε FA from 0.32” to 0.22”

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Exemple initialisation (ECMWF + MESO-NH après real step – basse et haute résolution verticale)

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SIMULATED VERTICAL PROFILES ABOVE DOME C Meteorological parameters (2) - At the surface: RadiosondesECMWF Wind speed (m/s) Temperature (K) 4.02 ± ± ± ± 5.83 MonomodelGrid-nesting 4.23 ± ± ± ± 4.97 Mean values of temperature and wind speed at the surface above Dome C for the 47 winter nights. -> Meso-NH better reproduces the surface temperature and wind speed at Dome C than the ECMWF analyses. -> The grid-nested high horizontal resolution configuration gives results closer to the observations than the low horizontal configuration.

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TEMPORAL EVOLUTION OF Cn² PROFILES -16 nights between 16 June 2005 and 21 September 2005 (winter) have been observed by Trinquet et al. (2008). We simulated these nights using the astro-meso-nh package developed by the team. - Examples of simulations for 3 of these nights: monomodel (top row) and grid-nested (bottom row) H (m AGL) Night Night 2Night H (m AGL) Night Night 2Night (UTC) (UTC) (UTC) Log(Cn²)

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SIMULATED VERTICAL PROFILES ABOVE DOME C Examples We show here the results for two different nights in winter (m/s) Wind speed (K) Potential temperature (m AGL) H (m AGL) Night Night 2 Log(Cn²) Vertical profiles at 12 UT, after 12 hours of simulation (UTC) (UTC) H (m AGL) Temporal evolutions of Cn² profiles

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MEDIAN Cn² VERTICAL PROFILE 20km m Measurements Monomodel Grid-nested Log(Cn²) Medians of the mean vertical profiles of Cn² (between 11 UT and 17 UT) over the 16 nights observed in Trinquet et al. (2008), above Dome C. For each night, using the Cn² vertical profile, we deduce the surface layer thickness of the Dome C site.

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SURFACE LAYER THICKNESS AT DOME C Winter Nights Surface Layer Thickness (m) Hsl (m) Mean values of Hsl: Observations: 34.2 m (Eq. 1) Monomodel (Eq. 1): 60.7 m / Monomodel (Eq.2): 72.1 m Grid-nested (Eq. 1): 46.8 m / Grid-nested (Eq. 2): 60 m

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SEEING Median values of the FA seeing: Observations: 0.3” Simulated (top 13 km): 0.46” Simulated (top 20 km): 0.53” Computed seeing (mean between 11 UT and 17 UT) for the same 16 nights. FA= free atmosphere, starts at: - 33 m in the observations; m in the simulations

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