Evaluation of the McCready Turbulence Sensor

Xia Feng

MS Defense

Dept of Atmospheric Sciences, University of Wyoming

One measure of atmospheric turbulence intensity is the eddy dissipation rate, e, which is related by the Kolmogoroff's inertial subrange hypothesis to the power spectral density of the wind components. McCready (1964) described an airborne instrument, which estimates e from the aircraft airspeed alone neglecting the ground speed in the wind equation. In this talk, we evaluate the McCready technique by comparison with e estimates using airspeed and groundspeed in the complete three-dimensional wind equation.

The analysis confirms that groundspeed has little variance at frequencies > 1 Hz on aircraft such as the University of Wyoming King Air (UWKA), a light twin-engine turboprop. Thus the estimates of e using airspeed only are valid.

The Universal Indicated Turbulence System (UITS) manufactured by Meteorology Research Incorporated (MRI) implements the McCready method. The principle of operation of the UITS is examined and numerically simulated. A comparison of the UITS with the full wind system on the UWKA is presented and the limitations of the UITS discussed. It is concluded that the UITS can provide estimates of e to within 5% of estimates from the full wind system.