Response properties of atmospheric turbulence measurement instruments using Russian research aircraft

Abstract

AbstractInstruments that measure atmospheric turbulence for the estimation of turbulent fluxes of heat, water vapor, and carbon dioxide were tested in the laboratory and during in‐flight conditions aboard a Russian research Ilyushin‐18 aircraft. The response characteristics of the aircraft turbulence sensors were first tested to decrease measurement errors for turbulent heat transfer and fluxes, including water vapour flux, before being installed on the Ilyushin‐18 aircraft that was used in joint Russian–Japanese atmospheric boundary‐layer research. The results show that the atmospheric turbulence measured in a frequency range of 0·01 to 10 Hz yielded proper estimates of fluxes. Errors in measurements of the turbulence made from the aircraft were also analysed. Aerodynamic distortions linked to the aircraft's body and propellers were determined from flight test experiments. Time lags between vertical wind speed fluctuations and air temperature fluctuations measured by the aircraft thermometer, and those between vertical wind speed fluctuations and air humidity fluctuations measured by an ultraviolet hygrometer (open‐path system) and an infrared hygrometer (closed‐path system) were estimated. The vertical wind speed and air temperature sensor measurements showed no time lag, but a time lag of 0·6 s occurred between vertical wind speed and ultraviolet hygrometer measurements. The time lag between vertical wind speed and the infrared hygrometer measurements depended on flight conditions due to air pumping load, and had to be defined for each sampling leg. Accounting for the time lag was critical for water vapour flux measurements and helped to eliminate large systematic errors. Copyright © 2004 John Wiley & Sons, Ltd.