Improved Airborne Hot-Wire Measurements of Ice Water Content in Clouds

Airborne measurements of ice water content (IWC) in both ice and mixed-phase clouds remain one of the long-standing problems in experimental cloud physics. For nearly three decades, IWC has been measured with the help of the Nevzorov hot-wire total water content (TWC) sensor, which had an inverted cone shape. It was assumed that ice particles would be captured inside the cone and then completely melt and evaporate. However, wind tunnel experiments conducted with the help of high-speed video recordings showed that ice particles may bounce out of the TWC cone, resulting in the underestimation of the measured IWC. The TWC sensor was modified to improve the capture efficiency of ice particles. The modified sensor was mounted on the National Research Council (NRC) Convair-580 and its measurements in ice clouds were compared with the measurements of the original Nevzorov TWC sensor, a Droplet Measurement Technologies (DMT) counterflow virtual impactor (CVI), and IWC calculated from the particle size distribution measured by optical array probes (OAPs). Results indicated that the IWC measured by the modified TWC hot-wire sensor as well as the CVI and that deduced from the OAP size distributions agreed reasonably well when the maximum size of ice particles did not exceed 4 mm. However, IWC measured by the original TWC sensor was approximately 3 times lower than that measured by the other three techniques. This result can be used for the retrieval of the past IWC measurements obtained with this TWC sensor. For clouds with ice particles larger than 4 mm, the IWC measured by the modified TWC sensor and CVI exhibited diverging measurements.