Wind speed vertical distribution at Mt Graham

The characterization of the vertical distribution of wind speed, V (h), is fundamental for anastronomical site for many different reasons: (i) the wind speed shear contributes to triggeroptical turbulence in the whole troposphere; (ii) a few of the astroclimatic parameters, suchas the wavefront coherence time (τ0), depend directly on V (h); (iii) the equivalent velocityV0, controlling the frequency at which the adaptive optics systems have to run in order towork properly, depends on the vertical distribution of the wind speed and optical turbulence.Also, too strong a wind speed near the ground can introduce vibrations in the telescopestructures. The wind speed at a precise pressure (200 hPa) has frequently been used to retrieveindications concerning τ0 and the frequency limits imposed on all instrumentation based onadaptive optics systems. However, more recently, it has been proved that V200 (the wind speedat 200 hPa) alone is not sufficient to provide exhaustive elements concerning this topic, andthus the vertical distribution of the wind speed is necessary. In this paper, we report on acomplete characterization of the vertical distribution of wind speed strength, which has beencarried out above Mt Graham (Arizona, USA), the site of the Large Binocular Telescope.We provide a climatological study extended over 10 yr using the operational analyses fromthe European Centre for Medium-Range Weather Forecasts (ECMWF). We prove that this isrepresentative of the vertical distribution of the wind speed at Mt Graham, with the exceptionof the boundary layer. We also prove that a mesoscale model can provide reliable nightlyestimates of V (h) above this astronomical site from the ground up to the top of the atmosphere(∼20 km).