Wavefront coherence time seasonal variability and forecasting at the San Pedro Mártir site

Abstract

Abstract. In order to efficiently use the recent astronomy high angular resolution techniques (Adaptive Optics and Interferometry) to correct the perturbed wavefront arriving at the telescope pupil, it is necessary to characterize a set of astroclimatic parameters. One of these is the wavefront coherence time τAO. It is an integral parameter, defining the maximum temporal correlation of the perturbed wavefront and it depends on the optical turbulence C 2 N (x, y, z) and the wind intensity |V (x, y, z)| in the whole troposphere. In this paper we use an atmospheric non-hydrostatic model (Meso-NH) conceived to simulate the classical meteorological parameters (p, T and V ) and adapted to simulate the optical turbulence (C 2 N ) to characterize the τAO in a region of some kilometers around the astronomical site of San Pedro Mártir (SPM) in Baja California (Mexico). We study the seasonal variability of the wind intensity in the whole atmosphere (20 km) above the SPM site during one year. We show that, using the C 2 N profiles simulated by Meso-Nh initialized with ECMWF (European Center for Medium Weather Forecasts) data, we obtain typical τAO values in the V band (λ = 0.5 µm). We calculate the seasonal variability of the τAO in SPM and also some preliminary results about the seasonal variability of C 2 N . Moreover, we suggest a physical explication of these variabilities. Finally we investigate the possibility of forecasting τAO.

Astroclimate at San Pedro Mártir - I. Seeing statistics between 2004 and 2008 from the Thirty Meter Telescope site-testing data

“…Results on the seeing and optical turbulence above the ground can be found in Avila, Vernin & Cuevas (), Echevarría et al (), Conan et al (), Avila et al (), Sánchez et al () and Avila et al (), and results on atmosphere modelling in Masciadri & Garfias (), Masciadri, Avila & Sánchez (, ), Masciadri et al () and Vogiatzis & Hiriart (). Extinction and opacity studies have also been performed by Schuster & Parrao (), Hiriart () and Parrao & Schuster ().…”

“…We now know that this site is one of the best astronomical locations in the world and it has been considered by the international astronomical community as a potential place for large telescopes to be built in the near future; it is a candidate site of projects such as Based on observations obtained at the Observatorio Astronómico Nacional at San Pedro Mártir, Baja California, México, operated by the Instituto de Astronomía, Universidad Nacional Autónoma de México. †E-mail: leonardo@astro.unam.mx in Masciadri & Garfias (2001), Masciadri, Avila & Sánchez (2002, 2004, Masciadri et al (2003) and Vogiatzis & Hiriart (2004). Extinction and opacity studies have also been performed by Schuster & Parrao (2001), Hiriart (2003) and Parrao & Schuster (2003).…”

Meteorological profiles and optical turbulence in the free atmosphere with NCEP/NCAR data at Oukaïmeden - I. Meteorological parameters analysis and tropospheric wind regimes

“…As already signalled by Tatarskii (1961), the atmosphere is prevalently stable during the nighttime and it is difficult to detect dynamic instabilities that cause the turbulence in strong wind shear. Furthermore, as proposed by Masciadri & Garfias (2001), following a statistical approach (VanZandt et al 1978; VanZandt, Gage & Warnock 1981), is replaced with a probability density function describing the stability and instability factors in the atmosphere provided by meteorological data at larger spatial scales. Then the probability density function for finding dynamical instability depends on the vertical gradient of wind and potential temperature () at larger scale (a few kilometres).…”

Optical turbulence vertical distribution with standard and high resolution at Mt Graham

“…The atmospheric models have been used for the first time to reconstruct and characterize the C 2 N profiles by Masciadri, Vernin & Bougeault (1999a,b). Since then, much progress has been achieved by our group: the model has been applied to different astronomical sites in a simple monomodel configuration (Masciadri, Vernin & Bougeault 2001; Masciadri & Garfias 2001) and more recently in a grid‐nesting configuration (Lascaux et al 2009), a new calibration technique has been proposed (Masciadri & Jabouille 2001) and statistically validated (Masciadri, Avila & Sanchez 2004) and the first application of the Meso‐Nh model as a tool of turbulence characterization has been presented (Masciadri & Egner 2006). However, so far we could always access GS measurements concentrated in a well‐defined period of time.…”