Elena Masciadri - Academia.edu (original) (raw)
Papers by Elena Masciadri
In the context of the MOSE project, in this contribution we present a detailed analysis of the Me... more In the context of the MOSE project, in this contribution we present a detailed analysis of the Meso-NH mesoscale model performances and their dependency on the model and orography horizontal resolutions in proximity of the ground. The investigated sites are Cerro Paranal (site of the ESO Very Large Telescope - VLT) and Cerro Armazones (site of the ESO European Extremely Large Telescope - E-ELT), in Chile. At both sites, data from a rich statistical sample of different nights are available - from AWS (Automated Weather Stations) and masts - giving access to wind speed, wind direction and temperature at different levels near the ground (from 2 m to 30 m above the ground). In this study we discuss the use of a very high horizontal resolution (dX=0.1 km) numerical configuration that overcomes some specific limitations put in evidence with a standard configuration with dX=0.5 km. In both sites results are very promising. The study is co-funded by ESO and INAF.
A characterization of the optical turbulence vertical distribution and all the main integrated as... more A characterization of the optical turbulence vertical distribution and all the main integrated astroclimatic parameters derived from the C2N and the wind speed profiles above Mt. Graham is presented. The statistic includes measurements related to 43 nights done with a Generalized Scidar (GS) used in standard configuration with a vertical resolution of ~1 km on the whole 20-22 km and with the new technique (HVR-GS) in the first kilometer. The latter achieves a resolution of ~ 20-30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C2N. A discretized distribution of the typical C2N profiles useful for the Ground Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis for the LBT Laser Guide Star system ARGOS case is done including the calculation of the 'gray zones' for J, H and K bands. Mt. Graham confirms to be an excellent site with median values of the seeing without dome contribution equal to 0.72", the isoplanatic angle equal to 2.5" and the wavefront coherence time equal to 4.8 msec. We provide a cumulative distribution of the percentage of turbulence developed below H* where H* is included in the (0,1 km) range. We find that 50% of the whole turbulence develops in the first 80 m from the ground. The turbulence decreasing rate is very similar to what has been observed above Mauna Kea.
The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ra... more The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ranging (Generalized SCIDAR) are two instruments conceived to measure the optical turbulence (OT) vertical distribution on the whole troposphere and low stratosphere (~ 20 km) widely used in the astronomical context. In this paper we perform a detailed analysis/comparison of measurements provided by the two instruments and taken during the extended site testing campaign carried out on 2007 at Cerro Paranal and promoted by the European Southern Observatory (ESO). The main and final goal of the study is to provide a detailed estimation of the measurements reliability i.e dispersion of turbulence measurements done by the two instruments at different heights above the ground. This information is directly related to our ability in estimating the absolute value of the turbulence stratification. To better analyse the uncertainties between the MASS and the GS we took advantage of the availability of measurements taken during the same campaign by a third independent instrument (DIMM - Differential Imaging Motion Monitor) measuring the integrated turbulence extended on the whole 20 km. Such a cross-check comparison permitted us to define the reliability of the instruments and their measurements, their limits and the contexts in which their use can present some risk.
The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually increased with decrea... more The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually increased with decreased contiguous field of view. This trade-off is dependent on the vertical profile of the optical turbulence (Cn2 profiles). It is known that the accuracy of the vertical distribution measured by existing Cn2 profiling techniques is currently quite uncertain for wide field performance predictions 4 to 20 arcminutes. With assumed uncertainties in measurements from Generalized-SCIDAR (GS), SODAR plus MASS we quantify the impact of this uncertainty on the trade-off between field of view and image quality for photometry of science targets at the resolution limit. We use a point spread function (PSF) model defined analytically in the spatial frequency domain to compute the relevant photometry figure of merit at infrared wavelengths. Statistics of this PSF analysis on a database of Cn2 measurements are presented for Mt. Graham, Arizona and Dome C, Antarctica. This research is part of the activities of ForOT (3D Forecasting of Optical Turbulence above astronomical sites).
Open Issues in Local Star Formation, 2003
We here review the structure and evolution of young stellar Herbig-Haro (HH) jets with the help o... more We here review the structure and evolution of young stellar Herbig-Haro (HH) jets with the help of fully 3-D hydrodynamical (HD) and magneto-hydrodynamical (MHD) simulations of radiative cooling jets, giving particular emphasis to the study of giant HH flows, and the effects of magnetic fields on the general jet structure. Also, we will discuss some relevant physical processes that arise from the interaction of these jets with the interestellar environment, like the entrainment of ambient molecular gas in the jet flow, and some implications of the numerical results on observed jet phenomena and the associated central sources.
Proceedings of SPIE - The International Society for Optical Engineering
ABSTRACT
It was recently shown (Masciadri et al. 2000, Masciadri 2001a), using a numerical simulation (Mes... more It was recently shown (Masciadri et al. 2000, Masciadri 2001a), using a numerical simulation (Meso-Nh model), that the hypothesis of considering horizontally uniform C N can have severe consequences. For example, the integration of the C N along lines of sight different from the zenith gives variations that can be larger than 0.50 . In this paper we try to validate this result following two approaches. (a) numerical approach: we compare measured and simulated C N profiles. The first ones were obtained with a Generalized Scidar (GS) and the latter are simulated with the Meso-Nh model at the same azimuth and elevation as those of the observations. Further measurements (DIMM, mast and balloons) are considered in order to support the comparison. (b) experimental approach: we compare C N profiles measured (almost simultaneously) by a GS along different lines of sight. The results of this study show that (1) the horizontal size of the turbulent layers can be finite, (2) the simulations an...
Se presentan resultados del monitoreo de perfiles de turbulencia óptica en San Pedro Mártir, Méxi... more Se presentan resultados del monitoreo de perfiles de turbulencia óptica en San Pedro Mártir, México, durante 11 noches en abril {mayo 1997 y 16 noches en mayo 2000. La velocidad de las capas turbulentas también se monitoreo, pero sólo durante la temporada del 2000. 6414 perfiles de turbulencia y 3016 perfiles de velocidad fueron medidos y analizados estadísticamente. Los resultados referentes a los perfiles de turbulencia son: (i) el seeing) producido en los primeros 1.2 km, sin incluir la turbulencia de cúpula, en los telescopios de 1.5 y 2.1 m tiene medianas de 0.0063 y 0.0044. (ii) La turbulencia por encima de 1.2 km y en la atmósfera completa produce seeing con valores medianos de 0.0038 y 0.0071. (iii) El ángulo de isoplanatismo para corrección total en óptica adaptativa tiene una valor mediano de 1.0087. (iv) La correlación temporal de la intensidad de la turbulencia cae a 50% en peródos de tiempo de 2 y 0.5 horas, aproximadamente, para alturas mayores y menores que 16 km sobr...
We present the results of a survey of young (<=300 Myr), close (= 10 mag (5 sigma) at a separa... more We present the results of a survey of young (<=300 Myr), close (= 10 mag (5 sigma) at a separation of 0.5 from the primary star on 45% of our targets and H band contrasts of 2 sigma. Followup observations were conducted on 8 < 2 sigma candidates (with separations of 3 - 15.5 AU and masses of 2-10 MJup,
Astrophysics and Space Science Library, 1997
Ground-based and Airborne Telescopes II, 2008
ABSTRACT Mesoscale model such as Meso-Nh have proven to be highly reliable in reproducing 3D maps... more ABSTRACT Mesoscale model such as Meso-Nh have proven to be highly reliable in reproducing 3D maps of optical turbulence (see Refs. 1, 2, 3, 4) above mid-latitude astronomical sites. These last years ground-based astronomy has been looking towards Antarctica. Especially its summits and the Internal Continental Plateau where the optical turbulence appears to be confined in a shallow layer close to the icy surface. Preliminary measurements have so far indicated pretty good value for the seeing above 30-35 m: 0.36&quot; (see Ref. 5) and 0.27&quot; (see Refs. 6, 7) at Dome C. Site testing campaigns are however extremely expensive, instruments provide only local measurements and atmospheric modelling might represent a step ahead towards the search and selection of astronomical sites thanks to the possibility to reconstruct 3D Cn2 maps over a surface of several kilometers. The Antarctic Plateau represents therefore an important benchmark test to evaluate the possibility to discriminate sites on the same plateau. Our group8 has proven that the analyses from the ECMWF global model do not describe with the required accuracy the antarctic boundary and surface layer in the plateau. A better description could be obtained with a mesoscale meteorological model. In this contribution we present the progress status report of numerical simulations (including the optical turbulence - Cn2) obtained with Meso-Nh above the internal Antarctic Plateau. Among the topic attacked: the influence of different configurations of the model (low and high horizontal resolution), use of the grid-nesting interactive technique, forecasting of the optical turbulence during some winter nights. Comment: 12 pages, 4 figures, SPIE 2008 conference
Ground-based and Airborne Telescopes II, 2008
Dome C is considered a site particularly suited for wide-field imaging thanks to its shallow surf... more Dome C is considered a site particularly suited for wide-field imaging thanks to its shallow surface turbulent layer and its weak turbulence in the free atmosphere. What is the quantitative gain one can hope to achieve at Dome C with respect to a mid-latitude site? With the point spread function model defined analytically in the spatial frequency domain we are better able to connect the morphological and statistical behaviour of the turbulence profile to the trade-off between the adaptive telescope's field of view and a figure of merit for survey rate. A familiar image quality figure of merit is the radius of 50% encircled energy, and for J-band images it quickly identifies the requirement that will make a Dome C telescope, 8 meters above the ice, competitive with a mid-latitude one. From the radius of 50% encircled energy we derive the wide-field survey rate equation to estimate the impact of uncertainty in the vertical distribution of ground-layer turbulence on the trade-off between field of view (in the domain 10-20 arcminutes) and their survey rate.
Ground-based and Airborne Telescopes II, 2008
The atmospheric properties above three sites on the Internal Antarctic Plateau are investigated f... more The atmospheric properties above three sites on the Internal Antarctic Plateau are investigated for astronomical applications calculating the monthly median of the analysis-data from ECMWF (European Centre for Medium-Range Weather Forecasts) for an entire year (2005) thus covering all seasons. Radiosoundings extended on a yearly time scale from Dome C and the South Pole are used to verify the reliability of the analyses in the free atmosphere and to study the wind speed in the first 100 m as the analysis-data are not optimized for this altitude-range. The wind speed in the free atmosphere is obtained from the ECMWF analyses from all three sites. It appears that the strength of the wind speed in the upper atmosphere in winter is correlated to the distance of the site from the centre of the polar high. The Richardson number is employed to investigate the stability of the free atmosphere and, consequently, the probability to trigger thermodynamic instabilities above the three sites. We find that, in a large majority of the cases, the free atmosphere over the Internal Antarctic Plateau is more stable than at mid-latitude sites. Given these data we can obtain a ranking of the three sites both with respect to wind speed, in the free atmosphere as well as in the surface layer, and with respect to the stability of the atmosphere, using the Richardson number.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
ABSTRACT During winter and springtime, the flow above Antarctica at high altitude (upper troposph... more ABSTRACT During winter and springtime, the flow above Antarctica at high altitude (upper troposphere and stratosphere) is dominated by the presence of a vortex centered above the continent. It lasts typically from August to November. This vortex is characterized by a strong cyclonic jet centered above the polar high. In a recent study1 of four different sites in the Antarctic internal plateau (South Pole, Dome C, Dome A and Dome F), it was made the hypothesis that the wind speed strength in the upper atmosphere should be related to the distance of the site to the center of the Antarctic polar vortex. This high altitude wind is very important from an astronomical point of view since it might trigger the onset of the optical turbulence and strongly affect other optical turbulence parameters. What we are interested in here is to localize the position of the minimum value of the wind speed at different heights in the troposphere, particularly above 10 km. For that we studied the analyses from the ECMWF for winter 2005 at different levels. We deduced a preferential position of this minimum, tilted with altitude, in a zone between South Pole and Dome A, for the year 2005. This extensive study over one entire winter confirms the "position space" of the polar high deduced by Ref. 1.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
ABSTRACT The characterization of the optical turbulence (OT) done with meso-scale models for astr... more ABSTRACT The characterization of the optical turbulence (OT) done with meso-scale models for astronomical applications is an alternative approach to this science that intrinsically presents some interesting and complementary features/advantages with respect to the characterization done with measurements. The most important advantages are namely: (1) the possibility to describe a 3D map of the CN2 in a region around a telescope, (2) the possibility to forecast the optical turbulence i.e. to know with some hours in advance the state of the turbulence conditions above an astronomical site and (3) the possibility to perform a climatology of the optical turbulence extended over decades. No other tool of investigation with comparable potentialities can be figured out at present to achieve these 3 scientific goals. The forecast of the optical turbulence is a fundamental requirement for the optimization of the management of the scientific programs to be carried out at ground-based telescopes foci. Ground-based astronomy will remain an appealing option for astronomers with respect to the spaced-based one only if the telescopes management will be performed taking advantage of the best turbulence conditions. The future of new ground-based telescopes generation relies therefore upon the success of these studies. ForOT is a scientific project but even more, it identifies a philosophic approach to studies related to the characterization of the optical turbulence in an astronomical context. In this contribution we will deal about the main success obtained so far in this discipline in the past, the new goals predetermined by ForOT and the main results we obtained so far. To conclude, we will trace a perspective at long time scale indicating where our research is addressed to and how the scientific community and the managers who lead the ground-based astronomical facilities can support our researchers to progress in these studies.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
EAS Publications Series, 2009
ABSTRACT It has already been demonstrated that a mesoscale meteorological model such as Meso-NH i... more ABSTRACT It has already been demonstrated that a mesoscale meteorological model such as Meso-NH is highly reliable in reproducing 3D maps of optical turbulence. Preliminary measurements above the Antarctic Plateau have so far indicated a pretty good value for the seeing: around 0.3&quot; at Dome C. However some uncertainties remain. That&#39;s why our group is focusing on a detailed study of the atmospheric flow and turbulence in the internal Antarctic Plateau. Our intention is to use the Meso-NH model to do predictions of the atmospheric flow and the corresponding optical turbulence in the internal plateau. The use of this model has another huge advantage: we have access to informations inside an entire 3D volume which is not the case with observations only. Two different configurations have been used: a low horizontal resolution (with a mesh-size of 100 km) and a high horizontal resolution with the grid-nesting interactive technique (with a mesh-size of 1 km in the innermost domain centered above the area of interest). We present here the turbulence distribution reconstructed by Meso-NH for 16 nights monitored in winter time 2005, looking at the the seeing and the surface layer thickness. Comment: 3rd Arena conference, 11-15 May 2009, EAS Publication Series
EAS Publications Series, 2007
ABSTRACT Due to the recent interest shown by astronomers towards the Antarctic Plateau as a poten... more ABSTRACT Due to the recent interest shown by astronomers towards the Antarctic Plateau as a potential site for large astronomical facilities, we assisted in the last years to a strengthening of site testing activities in this region, particularly at Dome C. Most of the results collected so far concern meteorologic parameters and optical turbulence measurements based on different principles using different instruments. At present we have several elements indicating that, above the first 20-30 meters, the quality of the optical turbulence above Dome C is better than above whatever other site in the world. The challenging question, crucial to know which kind of facilities to build on, is to establish how much better the Dome C is than a mid-latitude site. In this contribution we will provide some complementary elements and strategies of analysis aiming to answer to this question. We will try to concentrate the attention on critical points, i.e. open questions that still require explanation/attention. Comment: 3 figures, EAS Publications Series, Volume 25, 2007, pp.57
In the context of the MOSE project, in this contribution we present a detailed analysis of the Me... more In the context of the MOSE project, in this contribution we present a detailed analysis of the Meso-NH mesoscale model performances and their dependency on the model and orography horizontal resolutions in proximity of the ground. The investigated sites are Cerro Paranal (site of the ESO Very Large Telescope - VLT) and Cerro Armazones (site of the ESO European Extremely Large Telescope - E-ELT), in Chile. At both sites, data from a rich statistical sample of different nights are available - from AWS (Automated Weather Stations) and masts - giving access to wind speed, wind direction and temperature at different levels near the ground (from 2 m to 30 m above the ground). In this study we discuss the use of a very high horizontal resolution (dX=0.1 km) numerical configuration that overcomes some specific limitations put in evidence with a standard configuration with dX=0.5 km. In both sites results are very promising. The study is co-funded by ESO and INAF.
A characterization of the optical turbulence vertical distribution and all the main integrated as... more A characterization of the optical turbulence vertical distribution and all the main integrated astroclimatic parameters derived from the C2N and the wind speed profiles above Mt. Graham is presented. The statistic includes measurements related to 43 nights done with a Generalized Scidar (GS) used in standard configuration with a vertical resolution of ~1 km on the whole 20-22 km and with the new technique (HVR-GS) in the first kilometer. The latter achieves a resolution of ~ 20-30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C2N. A discretized distribution of the typical C2N profiles useful for the Ground Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis for the LBT Laser Guide Star system ARGOS case is done including the calculation of the 'gray zones' for J, H and K bands. Mt. Graham confirms to be an excellent site with median values of the seeing without dome contribution equal to 0.72", the isoplanatic angle equal to 2.5" and the wavefront coherence time equal to 4.8 msec. We provide a cumulative distribution of the percentage of turbulence developed below H* where H* is included in the (0,1 km) range. We find that 50% of the whole turbulence develops in the first 80 m from the ground. The turbulence decreasing rate is very similar to what has been observed above Mauna Kea.
The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ra... more The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ranging (Generalized SCIDAR) are two instruments conceived to measure the optical turbulence (OT) vertical distribution on the whole troposphere and low stratosphere (~ 20 km) widely used in the astronomical context. In this paper we perform a detailed analysis/comparison of measurements provided by the two instruments and taken during the extended site testing campaign carried out on 2007 at Cerro Paranal and promoted by the European Southern Observatory (ESO). The main and final goal of the study is to provide a detailed estimation of the measurements reliability i.e dispersion of turbulence measurements done by the two instruments at different heights above the ground. This information is directly related to our ability in estimating the absolute value of the turbulence stratification. To better analyse the uncertainties between the MASS and the GS we took advantage of the availability of measurements taken during the same campaign by a third independent instrument (DIMM - Differential Imaging Motion Monitor) measuring the integrated turbulence extended on the whole 20 km. Such a cross-check comparison permitted us to define the reliability of the instruments and their measurements, their limits and the contexts in which their use can present some risk.
The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually increased with decrea... more The image quality from Ground-Layer Adaptive Optics (GLAO) can be gradually increased with decreased contiguous field of view. This trade-off is dependent on the vertical profile of the optical turbulence (Cn2 profiles). It is known that the accuracy of the vertical distribution measured by existing Cn2 profiling techniques is currently quite uncertain for wide field performance predictions 4 to 20 arcminutes. With assumed uncertainties in measurements from Generalized-SCIDAR (GS), SODAR plus MASS we quantify the impact of this uncertainty on the trade-off between field of view and image quality for photometry of science targets at the resolution limit. We use a point spread function (PSF) model defined analytically in the spatial frequency domain to compute the relevant photometry figure of merit at infrared wavelengths. Statistics of this PSF analysis on a database of Cn2 measurements are presented for Mt. Graham, Arizona and Dome C, Antarctica. This research is part of the activities of ForOT (3D Forecasting of Optical Turbulence above astronomical sites).
Open Issues in Local Star Formation, 2003
We here review the structure and evolution of young stellar Herbig-Haro (HH) jets with the help o... more We here review the structure and evolution of young stellar Herbig-Haro (HH) jets with the help of fully 3-D hydrodynamical (HD) and magneto-hydrodynamical (MHD) simulations of radiative cooling jets, giving particular emphasis to the study of giant HH flows, and the effects of magnetic fields on the general jet structure. Also, we will discuss some relevant physical processes that arise from the interaction of these jets with the interestellar environment, like the entrainment of ambient molecular gas in the jet flow, and some implications of the numerical results on observed jet phenomena and the associated central sources.
Proceedings of SPIE - The International Society for Optical Engineering
ABSTRACT
It was recently shown (Masciadri et al. 2000, Masciadri 2001a), using a numerical simulation (Mes... more It was recently shown (Masciadri et al. 2000, Masciadri 2001a), using a numerical simulation (Meso-Nh model), that the hypothesis of considering horizontally uniform C N can have severe consequences. For example, the integration of the C N along lines of sight different from the zenith gives variations that can be larger than 0.50 . In this paper we try to validate this result following two approaches. (a) numerical approach: we compare measured and simulated C N profiles. The first ones were obtained with a Generalized Scidar (GS) and the latter are simulated with the Meso-Nh model at the same azimuth and elevation as those of the observations. Further measurements (DIMM, mast and balloons) are considered in order to support the comparison. (b) experimental approach: we compare C N profiles measured (almost simultaneously) by a GS along different lines of sight. The results of this study show that (1) the horizontal size of the turbulent layers can be finite, (2) the simulations an...
Se presentan resultados del monitoreo de perfiles de turbulencia óptica en San Pedro Mártir, Méxi... more Se presentan resultados del monitoreo de perfiles de turbulencia óptica en San Pedro Mártir, México, durante 11 noches en abril {mayo 1997 y 16 noches en mayo 2000. La velocidad de las capas turbulentas también se monitoreo, pero sólo durante la temporada del 2000. 6414 perfiles de turbulencia y 3016 perfiles de velocidad fueron medidos y analizados estadísticamente. Los resultados referentes a los perfiles de turbulencia son: (i) el seeing) producido en los primeros 1.2 km, sin incluir la turbulencia de cúpula, en los telescopios de 1.5 y 2.1 m tiene medianas de 0.0063 y 0.0044. (ii) La turbulencia por encima de 1.2 km y en la atmósfera completa produce seeing con valores medianos de 0.0038 y 0.0071. (iii) El ángulo de isoplanatismo para corrección total en óptica adaptativa tiene una valor mediano de 1.0087. (iv) La correlación temporal de la intensidad de la turbulencia cae a 50% en peródos de tiempo de 2 y 0.5 horas, aproximadamente, para alturas mayores y menores que 16 km sobr...
We present the results of a survey of young (<=300 Myr), close (= 10 mag (5 sigma) at a separa... more We present the results of a survey of young (<=300 Myr), close (= 10 mag (5 sigma) at a separation of 0.5 from the primary star on 45% of our targets and H band contrasts of 2 sigma. Followup observations were conducted on 8 < 2 sigma candidates (with separations of 3 - 15.5 AU and masses of 2-10 MJup,
Astrophysics and Space Science Library, 1997
Ground-based and Airborne Telescopes II, 2008
ABSTRACT Mesoscale model such as Meso-Nh have proven to be highly reliable in reproducing 3D maps... more ABSTRACT Mesoscale model such as Meso-Nh have proven to be highly reliable in reproducing 3D maps of optical turbulence (see Refs. 1, 2, 3, 4) above mid-latitude astronomical sites. These last years ground-based astronomy has been looking towards Antarctica. Especially its summits and the Internal Continental Plateau where the optical turbulence appears to be confined in a shallow layer close to the icy surface. Preliminary measurements have so far indicated pretty good value for the seeing above 30-35 m: 0.36&quot; (see Ref. 5) and 0.27&quot; (see Refs. 6, 7) at Dome C. Site testing campaigns are however extremely expensive, instruments provide only local measurements and atmospheric modelling might represent a step ahead towards the search and selection of astronomical sites thanks to the possibility to reconstruct 3D Cn2 maps over a surface of several kilometers. The Antarctic Plateau represents therefore an important benchmark test to evaluate the possibility to discriminate sites on the same plateau. Our group8 has proven that the analyses from the ECMWF global model do not describe with the required accuracy the antarctic boundary and surface layer in the plateau. A better description could be obtained with a mesoscale meteorological model. In this contribution we present the progress status report of numerical simulations (including the optical turbulence - Cn2) obtained with Meso-Nh above the internal Antarctic Plateau. Among the topic attacked: the influence of different configurations of the model (low and high horizontal resolution), use of the grid-nesting interactive technique, forecasting of the optical turbulence during some winter nights. Comment: 12 pages, 4 figures, SPIE 2008 conference
Ground-based and Airborne Telescopes II, 2008
Dome C is considered a site particularly suited for wide-field imaging thanks to its shallow surf... more Dome C is considered a site particularly suited for wide-field imaging thanks to its shallow surface turbulent layer and its weak turbulence in the free atmosphere. What is the quantitative gain one can hope to achieve at Dome C with respect to a mid-latitude site? With the point spread function model defined analytically in the spatial frequency domain we are better able to connect the morphological and statistical behaviour of the turbulence profile to the trade-off between the adaptive telescope's field of view and a figure of merit for survey rate. A familiar image quality figure of merit is the radius of 50% encircled energy, and for J-band images it quickly identifies the requirement that will make a Dome C telescope, 8 meters above the ice, competitive with a mid-latitude one. From the radius of 50% encircled energy we derive the wide-field survey rate equation to estimate the impact of uncertainty in the vertical distribution of ground-layer turbulence on the trade-off between field of view (in the domain 10-20 arcminutes) and their survey rate.
Ground-based and Airborne Telescopes II, 2008
The atmospheric properties above three sites on the Internal Antarctic Plateau are investigated f... more The atmospheric properties above three sites on the Internal Antarctic Plateau are investigated for astronomical applications calculating the monthly median of the analysis-data from ECMWF (European Centre for Medium-Range Weather Forecasts) for an entire year (2005) thus covering all seasons. Radiosoundings extended on a yearly time scale from Dome C and the South Pole are used to verify the reliability of the analyses in the free atmosphere and to study the wind speed in the first 100 m as the analysis-data are not optimized for this altitude-range. The wind speed in the free atmosphere is obtained from the ECMWF analyses from all three sites. It appears that the strength of the wind speed in the upper atmosphere in winter is correlated to the distance of the site from the centre of the polar high. The Richardson number is employed to investigate the stability of the free atmosphere and, consequently, the probability to trigger thermodynamic instabilities above the three sites. We find that, in a large majority of the cases, the free atmosphere over the Internal Antarctic Plateau is more stable than at mid-latitude sites. Given these data we can obtain a ranking of the three sites both with respect to wind speed, in the free atmosphere as well as in the surface layer, and with respect to the stability of the atmosphere, using the Richardson number.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
ABSTRACT During winter and springtime, the flow above Antarctica at high altitude (upper troposph... more ABSTRACT During winter and springtime, the flow above Antarctica at high altitude (upper troposphere and stratosphere) is dominated by the presence of a vortex centered above the continent. It lasts typically from August to November. This vortex is characterized by a strong cyclonic jet centered above the polar high. In a recent study1 of four different sites in the Antarctic internal plateau (South Pole, Dome C, Dome A and Dome F), it was made the hypothesis that the wind speed strength in the upper atmosphere should be related to the distance of the site to the center of the Antarctic polar vortex. This high altitude wind is very important from an astronomical point of view since it might trigger the onset of the optical turbulence and strongly affect other optical turbulence parameters. What we are interested in here is to localize the position of the minimum value of the wind speed at different heights in the troposphere, particularly above 10 km. For that we studied the analyses from the ECMWF for winter 2005 at different levels. We deduced a preferential position of this minimum, tilted with altitude, in a zone between South Pole and Dome A, for the year 2005. This extensive study over one entire winter confirms the "position space" of the polar high deduced by Ref. 1.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
ABSTRACT The characterization of the optical turbulence (OT) done with meso-scale models for astr... more ABSTRACT The characterization of the optical turbulence (OT) done with meso-scale models for astronomical applications is an alternative approach to this science that intrinsically presents some interesting and complementary features/advantages with respect to the characterization done with measurements. The most important advantages are namely: (1) the possibility to describe a 3D map of the CN2 in a region around a telescope, (2) the possibility to forecast the optical turbulence i.e. to know with some hours in advance the state of the turbulence conditions above an astronomical site and (3) the possibility to perform a climatology of the optical turbulence extended over decades. No other tool of investigation with comparable potentialities can be figured out at present to achieve these 3 scientific goals. The forecast of the optical turbulence is a fundamental requirement for the optimization of the management of the scientific programs to be carried out at ground-based telescopes foci. Ground-based astronomy will remain an appealing option for astronomers with respect to the spaced-based one only if the telescopes management will be performed taking advantage of the best turbulence conditions. The future of new ground-based telescopes generation relies therefore upon the success of these studies. ForOT is a scientific project but even more, it identifies a philosophic approach to studies related to the characterization of the optical turbulence in an astronomical context. In this contribution we will deal about the main success obtained so far in this discipline in the past, the new goals predetermined by ForOT and the main results we obtained so far. To conclude, we will trace a perspective at long time scale indicating where our research is addressed to and how the scientific community and the managers who lead the ground-based astronomical facilities can support our researchers to progress in these studies.
Optical Turbulence - Astronomy Meets Meteorology - Proceedings of the Optical Turbulence Characterization for Astronomical Applications, 2010
EAS Publications Series, 2009
ABSTRACT It has already been demonstrated that a mesoscale meteorological model such as Meso-NH i... more ABSTRACT It has already been demonstrated that a mesoscale meteorological model such as Meso-NH is highly reliable in reproducing 3D maps of optical turbulence. Preliminary measurements above the Antarctic Plateau have so far indicated a pretty good value for the seeing: around 0.3&quot; at Dome C. However some uncertainties remain. That&#39;s why our group is focusing on a detailed study of the atmospheric flow and turbulence in the internal Antarctic Plateau. Our intention is to use the Meso-NH model to do predictions of the atmospheric flow and the corresponding optical turbulence in the internal plateau. The use of this model has another huge advantage: we have access to informations inside an entire 3D volume which is not the case with observations only. Two different configurations have been used: a low horizontal resolution (with a mesh-size of 100 km) and a high horizontal resolution with the grid-nesting interactive technique (with a mesh-size of 1 km in the innermost domain centered above the area of interest). We present here the turbulence distribution reconstructed by Meso-NH for 16 nights monitored in winter time 2005, looking at the the seeing and the surface layer thickness. Comment: 3rd Arena conference, 11-15 May 2009, EAS Publication Series
EAS Publications Series, 2007
ABSTRACT Due to the recent interest shown by astronomers towards the Antarctic Plateau as a poten... more ABSTRACT Due to the recent interest shown by astronomers towards the Antarctic Plateau as a potential site for large astronomical facilities, we assisted in the last years to a strengthening of site testing activities in this region, particularly at Dome C. Most of the results collected so far concern meteorologic parameters and optical turbulence measurements based on different principles using different instruments. At present we have several elements indicating that, above the first 20-30 meters, the quality of the optical turbulence above Dome C is better than above whatever other site in the world. The challenging question, crucial to know which kind of facilities to build on, is to establish how much better the Dome C is than a mid-latitude site. In this contribution we will provide some complementary elements and strategies of analysis aiming to answer to this question. We will try to concentrate the attention on critical points, i.e. open questions that still require explanation/attention. Comment: 3 figures, EAS Publications Series, Volume 25, 2007, pp.57