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Optical turbulence simulations at Mt Graham using the Meso-NH model
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2011 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 412, no 4, 2695-2706 p.Article in journal (Refereed) Published
Abstract [en]

The mesoscale model Meso-NH is used to simulate the optical turbulence at Mt Graham (Arizona, USA), site of the Large Binocular Telescope. Measurements of the C2(N) profiles obtained with a generalized scidar from 41 nights are used to calibrate and quantify the model's ability to reconstruct the optical turbulence above the site. The measurements are distributed over different periods of the year, permitting us to study the model's performance in different seasons. A statistical analysis of the simulations is performed for all the most important astroclimatic parameters: the C2(N) profiles, the seeing epsilon, the isoplanatic angle theta(0) and the wavefront coherence time tau(0).

The model shows a general good ability in reconstructing the morphology of the optical turbulence (the shape of the vertical distribution of C2(N)) as well as the strength of all the integrated astroclimatic parameters. The relative error (with respect to measurements) of the averaged seeing on the whole atmosphere for the whole sample of 41 nights is within 9.0 per cent. The median value of the relative error night by night is equal to 18.7 per cent, so that the model still maintains very good performances. Comparable percentages are observed in partial vertical slabs (free atmosphere and boundary layer) and in different seasons (summer and winter). We prove that the most urgent problem, at present, is to increase the ability of the model in reconstructing very weak and very strong turbulence conditions in the high atmosphere. This evidence in the model mainly affects, at present, the model's performances for the isoplanatic angle predictions, for which the median value of the relative error night by night is equal to 35.1 per cent. No major problems are observed for the other astroclimatic parameters. A variant to the standard calibration method is tested but we find that it does not provide better results, confirming the solid base of the standard method.

Place, publisher, year, edition, pages
2011. Vol. 412, no 4, 2695-2706 p.
Keyword [en]
turbulence, atmospheric effects, methods, numerical, site testing
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-132797DOI: 10.1111/j.1365-2966.2010.18097.xISI: 000289295800046OAI: oai:DiVA.org:uu-132797DiVA: diva2:359206
Available from: 2010-10-27 Created: 2010-10-27 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Optical Turbulence Characterization for Ground-Based Astronomy
Open this publication in new window or tab >>Optical Turbulence Characterization for Ground-Based Astronomy
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The optical turbulence, which creates perturbations of the wavefronts coming from the stars, is caused by small-scale fluctuations in the index of refraction of the atmosphere and is a problem for astronomers because it limits the maximum resolution of the ground-based telescopes. One way of identifying the best sites to build astronomical observatories, where the influence of the optical turbulence is as small as possible, is to use the standard meteorological parameters to get a first idea of the potential of a site. In the first part of this thesis the three sites on the Internal Antarctic Plateau that are the most interesting for astronomers (Dome A, Dome C and the South Pole) are investigated using the operational analyses of the ECMWF and a ranking of these three sites is presented.

The second part of this thesis focuses on the ability of the mesoscale model Meso-NH to simulate the optical turbulence as well as the wind speed at Mt Graham (AZ, USA). A rich sample of measurements of the vertical distribution of the optical turbulence, the largest sample used in this type of study so far, is used to calibrate the Meso-NH model and to quantify its ability to simulate the optical turbulence. The measurements are distributed over different periods of the year thus making it possible to evaluate the performance of the model in different seasons. Both the vertical distribution of the optical turbulence and the astroclimatic parameters (seeing, wavefront coherence time and isoplanatic angle) are investigated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 68 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 778
Keyword
site testing, atmospheric effects, turbulence, optical turbulence, applied meteorology, mesoscale models
National Category
Meteorology and Atmospheric Sciences Astronomy, Astrophysics and Cosmology
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-132798 (URN)978-91-554-7926-8 (ISBN)
Public defence
2010-12-09, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 708Available from: 2010-11-17 Created: 2010-10-27 Last updated: 2011-03-21Bibliographically approved

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Hagelin, Susanna

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