The effects of probe-induced flow distortion on atmospheric turbulence measurements: extension to scalars

Abstract

I prove that in a steady velocity field the frequency spectrum of a conservative scalar is unaffected by flow distortion. This is a good approximation in turbulent flow if (qa1/3/U1l1/3)<< 1, where q and l are velocity and length scales of the energy-containing turbulence, a is the crossstream dimension of the body, and U1 is the mean flow speed. Criteria seem easily met for scalar mixing ratio measurements in typical aircraft applications but are more difficult to satisfy on towers. At aircraft speeds, crosstalk from air density fluctuations can seriously contaminate species density signals measured in regions of strong flow distortion. These errors can be very important in aircraft measurements of the vertical fluxes of CO2 and water vapor, whose sensors typically measure species density rather than mixing ratio. These errors can be minimized through boom design. Temperature measurements from aircraft can also be seriously affected by flow distortion. -from Author