Measurements of the Ice Water Content in Cirrus Using an Evaporative Technique

Abstract

A technique for the measurement of the ice water content (IWC) of cirrus clouds is described. The IWC is obtained by the measurement of the total water content (TWC) and the subtraction of the saturation specific humidity with respect to ice at the ambient pressure and temperature. The method is independent of the measurement of the crystal size spectrum and also of any assumptions about the bulk densities of various crystal habits. Examples of IWC measurements made during the International Cirrus Experiment are presented and compared with conventional measurements from a 2D optical array probe. The prime sources of error are the accuracy of the calibration of the TWC probe and the occurrence of subsaturated air, which invalidates one of the main principles of the technique.