Optical turbulence and wind speed distributions above the Tibetan Plateau from balloon-borne microthermal measurements

Abstract

ABSTRACT The vertical profiles of wind speed and the optical turbulence are critical to the design and operation of a new generation of highly sophisticated astronomical telescopes and adaptive optics instrumentation. We present the first study of the temporal evolution behaviours and probability distributions of wind speed [V(h) profiles, as well as the 200 hPa pressure level wind speed, V200] and optical turbulence [$C_n^2(h)$ profiles, and the most relevant integrated astronomical parameters derived from $C_n^2(h)$ profiles, i.e. the seeing ε, the isoplanatic angle θAO, the wavefront coherence time τAO, the average velocity of turbulence VAO, and the seeing layer height hAO] above the Dachaidan site of the Tibetan Plateau. The field campaigns of wind speed and optical turbulence were collected using the balloon-borne microthermal measurement system. From the whole field campaigns, the results are remarkable: The median VAO is 21.1 m s−1, the median V200 is 32.5 m s−1, the median hAO is 7566 m, the median ε is 1.04 arcsec (below 1.00 arcsec 52 per cent of the time), the median θAO is 0.74 arcsec, and the median τAO is 1.33 ms; these conditions are comparable to some of the best astronomical observatories in the world. In particular, the linear relationship of average velocity and 200 hPa level wind at this site is VAO = 0.627V200. In this study, we flag the temporal evolution and probability distribution feature of wind speed, optical turbulence profile, and the relevant integrated astronomical parameters for astronomical applications.