Statistics of turbulence profile at Cerro Tololo

Abstract

Results of 3-month continuous monitoring of turbulence profile and seeing at Cerro Tololo (Chile) in May-July 2002 are presented. Some 28000 low-resolution profiles were measured by a new MASS single-star turbulence monitor, accompanied by seeing data from DIMM. The median seeing was 0.95 arcseconds. The first 500 m contribute 60% to the total seeing, the free-atmosphere median seeing was 0.55 arcseconds. Free-atmosphere seeing is almost never better than 0.15 arcseconds because there is always some turbulence above 12 km. A 4-day period of calm upper atmosphere with a stable free-atmosphere seeing of 0.2-0.3 arcseconds was noted. A gain in resolution from adaptive compensation of ground layer will be 1.7 times typically and 2-3 times during such calm periods. Correlations of the free-atmosphere turbulence with the wind speed at tropopause and of the ground-layer turbulence with ground wind are studied. Temporal evolution of turbulence is characterized by recurrent bursts, their typical duration increases from 15 minutes in low layers to 1-2 hours in high layers. The large data base of turbulence profiles can be used to test meso-scale modeling of astronomical seeing.