Optical turbulence simulations at Mt Graham using the Meso-NH mode

TL;DR

This study uses the Meso-NH mesoscale model to simulate optical turbulence at Mt Graham, demonstrating good accuracy in reconstructing turbulence profiles and astroclimatic parameters, with some limitations in high-altitude turbulence prediction.

Contribution

It provides a comprehensive validation of the Meso-NH model for optical turbulence forecasting at Mt Graham, including calibration, seasonal analysis, and assessment of model performance.

Findings

Model reconstructs turbulence morphology and strength with errors within 9% for seeing.

Median night-to-night error for seeing is 18.7%, showing high reliability.

Challenges remain in accurately modeling high-altitude turbulence affecting the isoplanatic angle.

Abstract

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 CN2-profiles obtained with a generalized scidar from 41 nights are used to calibrate and quantify the model's ability to reconstruct the optical turbulence. 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 CN2-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 CN2) 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 %. The median value of the relative error night by night is equal to 18.7 %, 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 mainly affects 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 %. 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.