The CIRES Tethered Lifting System: A State-of-the-art Tethersonde for the Measurement and Study of the Structure, Dynamics, and Turbulent Properties of Atmospheric Boundary Layers

Understanding the various structures, turbulent properties, and dynamics characterizing atmospheric boundary layers is of the utmost importance for a large number of applications such as Numerical Weather Predictions, Transport & Diffusion, wind energy applications, as well as agricultural and aeronautical meteorology.

The tethered lifting system (TLS) is a specialty-designed tethersonde system that was developed by the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado to complement current measurement systems with unique high-resolution insitu measurements of temperature, velocity, and turbulence.

Specialty-designed low noise and low power hot-wire (HW) and cold-wire (CW) sensors used in conjunction with a custom-built 16 bit high-rate data acquisition cards measure with high accuracy and precision the changes and fine-scale fluctuations of temperature, windspeed, and turbulence. Inertial range turbulence metrics such as the temperature structure constant CT2 and energy dissipation ε are estimated via spectral processing. The high sensitivity of the detector, low noise properties of the CW/HW circuit cards, and high sampling rate capabilities of the digitizer, allow accurate measurements of high resolution profiles of turbulence at a vertical resolution of 0.5 m or better, and down to extremely weak levels of turbulence of C_T²~10^-7 K²m^-2/3 and ε~10^-8 m²s^-3 (1/10^th of a m ^oC and mm/s fluctuations). In addition to C_T² and ε, the turbulence payload can also measure critical turbulence and dimensionless parameters such as the Kolmogorov and Taylor microscales, the Ozmidov scale, temperature and velocity turbulent length scales, Reynolds number, and turbulent Froude number. The TLS is also ideally suited for accurate measurements of local vertical gradients of temperature and velocity and thus stability parameters such as the gradient Richardson number.

The TLS is not only highly complementary of current measuring systems such as instrumented meteorological towers and remote sensors but also, thanks to the unique resolution and unprecedented sensitivity of its temperature, velocity, and turbulence measurements, provide new research opportunities. Such research applications include the empirical verification of stably stratified turbulent scaling laws, the validation of remote-sensors measurements of turbulence profiles, an improved understanding of boundary layer (BL) structures and dynamics.

This seminar will begin with a technical presentation of the TLS system, its principle of operation, measurement performances, and calibration accuracies. The second part of the talk will cover some of the research applications that the TLS has been used for to date and will open the door to suggestions on how such a system could benefit the research interests of NCAR’s Mesoscale and Microscale Meteorology division as well as complement EOL’s current measurement capabilities.