Thermodynamics of icing cylinder for measurements of liquid water content in supercooled clouds

The Rosemount Icing Detector (RICE) has been used extensively over the last three decades for aircraft measurements of the rate of ice riming in supercooled liquid and mixed clouds. Because of difficulties related to calibration and postprocessing, the RICE probe was mainly used as an indicator of the presence of supercooled liquid water. The accuracy of the RICE probe for measurements of supercooled liquid water content is studied here. The theory of ice accretion on an unheated cylinder is applied to the RICE probe. A steady-state heat balance on the surface of a riming cylinder is considered in detail. It is shown that the threshold sensitivity of the RICE probe is limited by the rate of sublimation of ice and it may exceed 0.01 g m^-3 at airspeed 200 m s^-1. The rate of ice sublimation limits the use of the RICE probe for measurements of low liquid water contents in clouds. The maximum possible measured liquid water content is restricted by the Ludlam limit. A new calibration technique of the RICE probe, based on the measurements of the rate of ice sublimation in cloud-free air, is developed here. The calibration coefficient derived using the "sublimation" technique is compared to that obtained using the conventional technique, that is, when ice is accreting on the cylinder. The sublimation technique was found to be more accurate compared to the conventional one. The accuracies of both methods are discussed.