Laboratory Calibration of a Vibrating Wire Device for Measuring Concentrations of Supercooled Liquid Water

Abstract

Laboratory measurements of supercooled liquid water are made by a vibrating-wire sensor whose frequency of vibration varies according to the mass of ice collected on it. The vibrating-wire system is designed to be placed in the humidity duct of VIZ type radiosondes. Supercoolod clouds were generated by injecting steam into a cold room. Measurements were made using a rotating arm to generate velocities comparable to rising radiosonde balloons. Supercooled liquid water concentrations found from the vibrating-wire measurements were compared with a standard measurement based upon a high speed rotating rod. Based upon the vibrating frequency measurements and comparisons with the ice weights collected by the rotating rod, it is concluded that the vibrating-wire system measures supercooled liquid water concentration in agreement with a control measurement. The rate of frequency change found in these approximately steady-state conditions over a 2-minute interval (to correspond with the control measurement) remains essentially the same even when the time interval is reduced to 15 s, giving a vertical resolution of 75 m for a balloon rise speed of 5 m s?1. At smaller time intervals, the rate of frequency change becomes progressively more variable as the time interval is reduced.