EDP Sciences
Free access
Volume 366, Number 2, February I 2001
Page(s) 708 - 716
Section Instruments, observational techniques and data processing
DOI http://dx.doi.org/10.1051/0004-6361:20000110

A&A 366, 708-716 (2001)
DOI: 10.1051/0004-6361:20000110

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

E. Masciadri and T. Garfias

Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apartado Postal 70-264, 04510 D.F., Mexico

(Received 30 August 2000 / Accepted 14 November 2000)

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 $\tau_{\rm AO}$. It is an integral parameter, defining the maximum temporal correlation of the perturbed wavefront and it depends on the optical turbulence $C_{\rm N}^2 $(x, y, z) and the wind intensity $\mid$ $\mathbf{\vec{V}}$(x, y, z)$\mid$ 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 $\mathbf{\vec{V}}$) and adapted to simulate the optical turbulence ( $C_{\rm N}^2 $) to characterize the $\tau_{\rm AO}$ 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_{\rm N}^2 $ profiles simulated by Meso-Nh initialized with ECMWF (European Center for Medium Weather Forecasts) data, we obtain typical $\tau_{\rm AO}$ values in the V band ($\lambda$ = 0.5 $\mu$m). We calculate the seasonal variability of the $\tau_{\rm AO}$ in SPM and also some preliminary results about the seasonal variability of $C_{\rm N}^2 $. Moreover, we suggest a physical explication of these variabilities. Finally we investigate the possibility of forecasting $\tau_{\rm AO}$.

Key words: atmospheric effets -- site testing -- instrumentation: interferometers; adaptive optics

Offprint request: E. Masciadri, elena@astroscu.unam.mx

© ESO 2001