New microphysics sensor for aircraft use

Abstract

A new optical sensor, PVM-100A, for aircraft cloud-microphysical measurements is described. The sensor measures the liquid water content (LWC), the integrated particle surface area (PSA) and the effective droplet radius r e of cloud droplets. The measurements are simultaneous, are made on a cloud volume of 1.25 cm 3, are made in situ and in real time, and have a maximum bandwidth of 5 KHz. Results are presented of calibrations of the PVM-100A in the fog-wind tunnel at ECN, Petten, The Netherlands where the LWC channel was compared to gravimetric measurements of droplets collected in filters, and the PSA channel was compared to measurements made with a corrected FSSP-100. The PVM-100A, CSIRO (King) and Johnson-Williams hot-wire probes, and another FSSP-100 were compared on flights made with the University of Washington C-131A aircraft in stratocumulus clouds during the 1992 ASTEX experiment near the Azores. The hot-wire probes were unable to resolve fine features in broken clouds, because of insufficient time response; the uncorrected FSSP-100 underestimated LWC when either LWC or droplet sizes was large and the measurements of r e made with the FSSP-100 and PVM-100A showed a large systematic difference. A simple method is proposed for retrieving acuurate FSSP-100 droplet spectra using the difference and PVM-10A measurements of LWC.