A Balloonborne Instrument for the Measurement of Vertical Profiles of Supercooled Liquid Water Concentration

Abstract

A vibrating wire placed in the humidity duct of a standard U.S. rawinsonde is used to measure vertical profiles of the concentration of supercooled liquid water in clouds. The natural frequency of vibration varies according to the mass of ice accumulated by contact freezing. By monitoring the natural frequency and the airspeed relative to the wire, the supercooled liquid water concentration can be found. Suitable electronics are developed for both individual expendable rawinsonde units and a ground-based receiver so that the vibration frequency can be recorded. Calibration of the frequency change versus mass accumulation is done theoretically along with measurements made in a wind tunnel with supercooled water present. Further verification is found by the use of paint, uniformly sprayed on the ?upwind? side of an exposed wire. For exposition of the instrument, a sample sounding is described.