This study presents observational data that are used to relate the cross-sectional area of an ice particle to its maximum diameter (D), for a number of individual particle habits and for natural mixed habit populations of ice particles in midlatitude, continental, synoptically generated cirrus clouds. The cross-sectional area is expressed in terms of the shape-sensitive parameter "area ratio" (Ar), which is the ratio of a particle's projected cross-sectional area to the area of a circle having the particle's maximum diameter. The Ar(D) relationships for particles of a specific habit are derived from several diverse datasets, including high-resolution Cloud Particle Imager (CPI), Particle Measuring System, Inc., 2D-C (cloud) and 2D-P (precipitation) probes and balloon-borne replicator in situ data in the temperature range -25°C to -65°C, ice particles collected at the surface, and ice particles grown in a wind tunnel. The Ar(D) relationships for cirrus clouds are derived from CP1, 2D-C, and 2D-P data during Lagrangian spiral descents, and from balloon-borne ice crystal replicator data. The dependence of the coefficients of the Ar(D) relationship on the fractional position between cloud base and cloud top is examined and related to microphysical processes operating in the clouds. Fundamental aspects of ice particle growth and the aggregation process are also examined. The area ratio is found to decrease systematically with increasing particle diameter for most individual particle habits and for natural cirrus cloud populations. The area ratio decreases rapidly with increasing diameter for particles smaller than about 500 μm, then more slowly for larger particles. The aggregation process produces particles with higher area ratios than single particles of the same diameter, and since most particles larger than 500-1000 μm are aggregates, aggregation leads to a decrease in the slope of Ar(D) at diameters greater than about 500 μm. The Ar(D) relationships are adequately represented by power-law expressions. The coefficients of the power-law Ar(D) relationship are roughly constant with height in the lower half of the cirrus clouds studied, but dependent on height in the upper half of the cloud column. The height dependence of Ar(D) is attributed to the impact of particle growth, aggregation, and sublimation on the particle shape and other particle characteristics. Profile measurements from 10 cirrus clouds are combined to produce a single parameterization for the mean Ar(D) trend, and for the dependence of its coefficients on fractional height within the normalized cloud column. An approach is given for using the Ar(D) relationships together with particle size distribution measurements or parameterizations to derive bulk cloud properties of importance to the modeling and radiative transfer communities. © 2003 American Meteorological Society.
CITATION STYLE
Heymsfield, A. J., & Miloshevich, L. M. (2003). Parameterizations for the cross-sectional area and extinction of cirrus and stratiform ice cloud particles. Journal of the Atmospheric Sciences, 60(7), 936–956. https://doi.org/10.1175/1520-0469(2003)060<0936:PFTCSA>2.0.CO;2
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