Quick look of optical turbulence measurements in the T-REX campaign

The Air Force Research Laboratory measured optical turbulence from the surface to 30km using the thermosonde in a portion of the T-REX Campaign. Participation began 20 March 2006 and continued through 6 April, which included IOPs 6 through 9. The objective of the AF participation was to study turbulence associated with mountain waves. The instruments were launched from the windward side of the Sierra Nevada Mountains near Three Rivers California.

The AFRL thermosonde estimates the optical turbulence profile by measuring a 1m horizontal temperature structure function as it ascends through the atmosphere 110m below a large weather balloon. The temperature differences are sensed by two 3.45 micro meter diameter tungsten wires which are legs of a Wheatstone bridge detecting the difference in temperature to 0.001K. Onboard instrumentation computes a 4 to 8 second running root-mean-square of the difference, which is transmitted to the ground station as spare channel data along with the met data from the attached RS-80GE radiosonde. The temperature structure function is converted to the temperature structure constant assuming that the turbulence follows Kolmogorov behavior and using Obukhov and Yaglom's deduction for passive scalars. The radiosonde data is then used to convert the temperature structure constant to the structure constant for the index of refraction, Cn2, the measure of local optical turbulence.

Eighteen thermosondes were launched with their radiosondes, 17 of which had usable Cn2 data, and 23 additional radiosondes were launched. Rawinsonde data from all launches will be used to detect mountain wave parameters to include variance in ascent rate, horizontal wind velocity, and potential temperature. Where possible, the optical turbulence strength will be tested for correlation with the wave parameters. In addition, there will be comparisons to various numerical model forecasts and possibly to other measurements in the T-REX Campaign.