Optical properties of shallow tropical cumuli derived from ARM ground-based remote sensing

This paper presents results from ground-based remote sensing of optical properties of shallow convective clouds over the Nauru ARM site using the technique developed by McFarlane et al. (2002). Herein, the results of a pilot study are presented with analysis of about six months of cloud data. The effective radius r_e shows large spatial variability, with the frequency of occurrence relatively narrow near the cloud base, and gradually widening aloft. Available column data for LWC and r_e allow derivation of the pdf of the optical thickness τ. The pdf shows that clouds with τ in the range 5 to 10 are most frequent, but there is a long tail with clouds up to τ = 100. These results are discussed in the context of traditional observations of cloud microstructure using an instrumented aircraft.