Generalized SCIDAR Measurements at San Pedro Mártir. II. Wind Profile Statistics
Résumé
We present the results of monitoring the speed of optical turbulent layers in the atmosphere above San Pedro Mártir, Mexico, during 15 nights in 2000 May. The data were obtained using the generalized scintillation detection and ranging technique (generalized SCIDAR), developed at Nice University. This paper constitutes the second in a series. The first paper presents results concerning measurements of optical turbulence strength obtained at the same site and time. The principal results of the present article are as follows: (1) The wind profiles remain stable during each night. (2) No correlation between the turbulence intensity C2N and the speed of the turbulent layers, V, is detected for speeds lower than ~45 m s-1. Above that speed, which was only exceeded in the jet-stream layer on one night, the optical turbulence strength is seen to increase. (3) Layers in the first 4 km and higher than 16 km above sea level are similarly slow, with median speeds of 8.6 and 9.6 m s-1, respectively. (4) Between 9 and 16 km, where the jet stream flows on some of the nights, the median wind speed is 26.0 m s-1. (5) From simultaneous measurements of C2N(h) and V(h), we compute the temporal coherence of the turbulence, layer by layer, in 500 m thick layers. This is the first time that such data have been published. For a multiconjugate adaptive optics system, our measurements show that the temporal responses of three deformable mirrors conjugated on the ground and at 6 km and 13 km above sea level, each one correcting for the turbulence in 500 m thick layers, would need to be 64, 40, and 20 ms. (6) The vertical variation of V dominates the vertical variation of the coherence time. (7) For the first time, we compare wind velocity profiles obtained from three different sources: generalized SCIDAR, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, and meteorological research balloons. The comparison shows excellent agreement in both the modulus and the direction of the wind velocity.