Analysis of Supercooled Liquid Water Measurements Using Microwave Radiometer and Vibrating Wire Devices

Abstract

A review is made of the theoretical basis for using a vibrating wire to measure supercooled liquid water in clouds. The device consists of a vibrating wire and associated electronics added to radiosondes. The sensing wire that collects supercooled liquid water as rime ice is placed in a specially designed duct to minimize effects from swinging of the balloon as it ascends. Profiles of supercooled liquid water are vertically integrated, so that comparisons with radiometer measurements may be made. Because the radiometer senses all liquid whether from supercooled water, melting snow, or rain, any comparisons are valid only when the entire viewing path of the radiometer remains below 0°C. Comparisons of supercooled liquid water measurements by the vibrating wire and a microwave radiometer show that the two methods are in good agreement. Even better agreement is obtained when the effect of a variable cloud radiation temperature on the radiometer measurement is taken into account. The remaining differences between the two measuring systems are attributed primarily to the different viewing paths, vertical for the radiometer and the balloon path for the vibrating wire. These results along with previous laboratory calibrations of the vibrating wire lead to the conclusion that the vibrating wire sensor included in radiosondes is suitable to obtain vertical (balloon path) profiles of supercooled liquid water. It is also concluded that use of the radiosonde device and a microwave radiometer is a powerful combination for obtaining and analyzing data on supercooled liquid water.