The astroclimate of Maidanak Observatory in Uzbekistan

The atmospheric turbulence and meteorology of the Maidanak Observatory in Uzbekistan are reviewed. Night time seeing was measured during the period August 1996 - November 1999 with the ESO Differential Image Motion Monitor. The median zenith seeing (FWHM.) for the entire period of observations is 0.69 " at 0.5 mu m. A maximum clear sky season for Maidanak is July September, with about 90% of possible clear time and a median seeing of 0.69 ". The best monthly median seeing, 0.62 ", is observed in November, The winter maximum of clear time is usually observed in February (up to 50%) with a FWHM of 0.77 ". During an additional site testing campaign (9 nights) organized in July 1998, the median wavefront, outer scale L-0 of 25.9 m and a median isoplanatir angle theta(0) of 2.48 " were measured with the Generalized Seeing Monitor developed at the University of Nice. The temporal evolution of the wavefront can be described by several layers moving at slow velocities with predominant direction from the West. This corresponds tu a remarkably large atmospheric time constant. No correlation between wavefront velocity and the willd velocity at ground level was found. The good seeing, large isoplanatic angle and, especially, slow wind, place Maidanak Observatory among the best international astronomical sites fur high angular resolution observations by interferometry and adaptive optics.