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Distributions of total water in cirrus provide important information on cloud-scale variability. Observations of water variables in cirrus are sparse, limiting our ability to constrain factors controlling their evolution and lifetimes. We present and analyze aircraft measurements of tropical and extratropical cirrus total water statistics. We show that observed distributions are replicated by a parametric model that only requires knowledge of in-cloud temperatures. We parameterize the temporal decay of cloud ice content and distribution skewness forced by ice crystal sedimentation and find that ice water content decays at a much faster rate than skewness in the absence of cloud ice and skewness sources. The sensitivity of skewness to changes in ice water content is small. Our methodology and findings may prove useful for studies addressing statistical cloud schemes and cirrus life cycles.

Plain Language Summary Probability distributions are important modeling tools to describe the atmospheric effects of clouds. This study reports distributions of total (gas plus ice phase) water in high tropospheric ice clouds (cirrus) obtained from measurements with research aircraft in tropical, midlatitude, and Arctic locations. We make a first attempt to base the origin of the distributions on physical processes and to reconstruct them with a statistical approach based on knowledge of cloud temperatures. We thereby show that the observed, heavy tails of the total water statistics are linked to the presence of cloud ice crystals. While cloud ice mass diminishes by ice crystal settling, the tails decay at a much slower rate. We hope that our methodology proves to be useful in support of studies analyzing cirrus life cycles.