The results on the vertical distribution of optical turbulence above the five mountains which were investigated by the site testing for the Thirty Meter Telescope (TMT) are reported. On San Pedro Martir in Mexico, the 13 North site on Mauna Kea and three mountains in northern Chile Cerro Tolar, Cerro Armazones and Cerro Tolonchar, MASS-DIMM turbulence profilers have been operated over at least two years. Acoustic turbulence profilers - SODARs - were also operated at these sites. The obtained turbulence profiles indicate that at all sites the lowest 200m are the main source of the total seeing observed, with the Chilean sites showing a weaker ground layer than the other two sites. The two northern hemisphere sites have weaker turbulence at altitudes above 500m, with 13N showing the weakest 16km turbulence, being responsible for the large isoplanatic angle at this site. The influence of the jetstream and wind speeds close to the ground on the clear sky turbulence strength throughout the atmosphere are discussed, as well as seasonal and nocturnal variations. This is the sixth article in a series discussing the TMT site testing project.Comment: 36 pages, 14 figures, accepted for publication in PAS

The multiaperture scintillation sensor (MASS) has become a device widely employed to measure the altitude distribution of atmospheric turbulence. An empirical study is reported that investigates the dependence of the MASS results on the knowledge of the instrumental parameters. Also, the results of a side-by-side comparison of two MASS instruments are presented, indicating that MASS instruments permit measurements of the integrated seeing to a precision better than 0:05 arc sec and of the individual turbulence layer strength C 2 n ðhÞdh to better than 10 −14 m 1=3 .

Seeing stability is an important criterion of site characterization. Two sites, with the same seeing statistics, could in principle differ in their temporal stability and hence have their observatories perform differently. Temporal variability can, however, be defined in several ways, all of which may determine the performance of the observatories in different manner. In this paper, we propose three methods to measure variability each focusing on different applications: Selection (maximization of observation time), Image quality (seeing variation within a given integration time) and finally Scheduling (prediction of seeing fluctuation on a given time scale). We apply these methods to the seeing of the TMT candidate sites to determine their stability properties.

One of the main tools used in the TMT site testing campaign is the turbulence profiler MASS. We describe empirical investigations and a side by side comparison of two MASS systems which were performed in order to identify the accuracy of MASS turbulence data and its dependence on the instrument calibration. The accuracy of the total seeing delivered by the TMT MASS systems is found to be better than 0"05. The combination of MASS and DIMM allows to observe the seeing within the first few hundred meters of the atmosphere and can be used to investigate possible correlations with meteorological parameters measured close to the ground. We also compare the detection of clouds and cirrus by means of MASS data (LOSSAM method) with measurements of the thermal emission of clouds using a net radiation sensor. These methods are compared with the visual cloud detection using all sky cameras.