Calibration of the Cloud Extinction Probe and some results of measurements

Description

Theoretical and laboratory study of the accuracy of the extinction coefficient measured by the newly developed Cloud Extinction Probe (CEP) are discussed. The Cloud Extinction probe utilizes the transmissiometric method. This method enables the calculation of the extinction coefficient from first principles based on the Beer-Bouguer law. In spite of the high sensitivity (~0.2km-1), the question about the effect of the size of cloud particles on the measured extinction coefficient remains open. In the case of large cloud particles, the CEP may underestimate the extinction coefficient due to receiving extra light caused by the narrow forward-scattering lobes and limited receiving aperture of the Extinction probe. A laboratory installation was developed for calibration of the extinction probe in the frame of the ARM Aerial Instrument proposals #09-5755 and used for the study of the effect of forward-scattering on the CEP measurements. The extinction probe has been installed on the NRC Convair 580 and participated in 26 flights during the DOE ARM ISDAC project in Alaska during April 2008. The results of this work will be used for the parameterization of the extinction coefficient in Arctic ice and mixed-phase clouds.