Using large-eddy simulation to investigate intermittency fluxes of clear-air radar reflectivity in the atmospheric boundary layer

Clear-air Doppler radars, also known as clear-air radar windprofilers, have been used for decades to remotely monitor wind velocities in the troposphere, stratosphere, and mesosphere. The traditional assumption is that the Doppler velocity (the first normalized moment of the Doppler spectrum) is an unbiased measure of the radial wind velocity within the radar's observation volume. Here we show that “intermittency fluxes”, i.e., covariances of the turbulently fluctuating clear-air radar reflectivity and the turbulently fluctuating radial wind velocity, lead to systematic differences between the Doppler velocity and the (true) radial wind velocity. We use turbulent fields computationally generated by means of a large-eddy simulation to quantify this effect. We show that these biases may amount to several tens of centimeters per second in the atmospheric boundary layer, which is consistent with the biases observed with vertically pointing boundary-layer radar windprofilers.