ON THE CALTECH ACTIVE STRAND CLOUDWATER COLLECTORS

A detailed analysis of several versions of the Caltech Active Strand C loudwater Collector (CASCC) is conducted. Efficiency calculations, des ign considerations and procedures for cloud liquid water content estim ation from the collection rates of these instruments are discussed. Th e size-fractionating CASCC is capable of simultaneous collection of sa mples representing two portions of the cloud drop size spectrum. Large drops are collected in an inlet stage while smaller drops are collect ed in a second stage. Theoretical calculations, which assume no aerody namic interaction between adjacent rows of collection rods in the inle t, suggest the inlet should have a 50% size cut corresponding to a dro p size of 23 mu m diameter. However, field test results suggest that f ocusing of the flow passing through a row of cylinders may increase th e efficiency of collection on the subsequent cylinder row, thereby dec reasing the overall size cut for the inlet. The CASCC2, a compact vers ion of the original CASCC, is designed to sample the entire cloud drop spectrum. Comparison of the cloudwater collection rates of the CASCC2 and the size-fractionating CASCC showed good agreement when normalize d by the flow rare through each collector. The Caltech Heated Rod Clou dwater Collector (CHRCC), designed for use in supercooled clouds, feat ures a theoretical 50% lower size cut corresponding to a drop diameter of 9 mu m. Liquid water content values estimated from the CHRCC cloud water collection rates correlated reasonably well with values measured with a Gerber Particle Volume Monitor (PVM-100) in both warm (r(2) = 0.83) and supercooled (r(2) = 0.71) cloud conditions.