Profiles of optical extinction coefficients calculated from droplet spectra observed in marine stratus cloud layers

Airborne measurements of droplet spectra n(r) where r is droplet radius were made in stratus cloud layers over the ocean 130 km southwest of San Diego. Optical extinction coefficients sigma sub(e) were calculated as selected wavelengths ( lambda = 0.53, 3.75 and 10.59 mu m) from these n(r) and were used to construct average vertical profiles of sigma sub(e) between 200 m above cloud base to 250 m below could base. An approximation to sigma sub(e), a power function of the liquid water content w, was found to be superior compared with approximations involving linear functions of w or the cross-section area. The horizontal variability of sigma sub(e) in the clouds was examined. The average horizontal scale size of sigma sub(e) was estimated to be 3 km and the horizontal measuring distance required to obtain values of sigma sub(e) with a relative accuracy of 10% was found to be in excess of 30 km.