In Situ Observations of Cirrus Cloud Microphysical Properties Using the Counterflow Virtual Impactor

Abstract

This study presents a new technique for making in situ measurements of cirrus cloud microphysical properties. Sampling of cirrus clouds was performed using a counterflow virtual impactor (CVI). The CVI was used to sample cloud elements larger than 4 µm in aerodynamic diameter. In conjunction with a Lyman-α hygrometer, this gave a direct measurement of the condensed water content. Sampling the cloud elements with the CVI also allowed the authors to examine the size distribution of the residual particles produced by evaporation of the cloud elements. This study discusses and evaluates the CVI technique for use in sampling cirrus clouds, especially for sampling small cloud elements. Measurements of condensed water content and cloud-element (crystal and droplet) concentrations for cirrus uncinus, floccus, and cirrostratus clouds made using the CVI during the International Cirrus Experiment experiment are presented. Examples of size distributions of the residual aerosol particles from cirrus cloud elements are also presented.