Thirty Meter Telescope Site Testing VI: Turbulence Profiles

TL;DR

This study compares optical turbulence profiles at five potential TMT sites, revealing ground-layer turbulence as the main seeing factor and highlighting differences in high-altitude turbulence and seasonal variations.

Contribution

It provides detailed turbulence profiles for five sites, including ground and high-altitude layers, using MASS-DIMM and SODAR measurements over multiple years.

Findings

Chilean sites have weaker ground-layer turbulence.

13N site exhibits the weakest high-altitude turbulence.

Turbulence strength varies seasonally and with wind conditions.

Abstract

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.