Coherence time and turbulence velocity at the Roque de los Muchachos Observatory from G-SCIDAR turbulence profiles and operational radiosounding wind speed.

Abstract

The coherence time (τ 0) is one of the relevant atmospheric optical parameters for the design of AO systems, being directly related with the band width and the stability requirements. A proper retrieval of τ 0 implies the combination of vertical turbulence and wind profiles. In this work we have used 140 nights of G-SCIDAR C 2 n (h) turbulence profiles obtained at the Roque de los Muchachos Observatory (ORM) and wind profiles from simultaneous operational radiosounding balloons launched from the neighbour island of Tenerife (∼ 155 km distant) at midnight by the Spanish Meteorological Agency (AEMet). The wind data have been processed to retrieve the average velocity of the turbulence (V 0) for each night. Here we present the statistical results of τ 0 and V 0 for the ORM and median monthly vertical profiles of wind speed for the Canary Islands. The median τ 0 is 4.9 ms, with quartiles P25=2.9 ms and P75=6.5 ms. The same values for V 0 are 6.2, 9.5 and 12.4 m/s for P25, P50 and P75, respectively. The average wind profile shows a maximum driven by the Tropopause at an altitude ranging from 10 to 12 km over the Observatory.