Characterization of mixed-phase clouds

Mixed-phase, ice, and liquid water clouds were characterized using two constant temperature sensors for approximately 81 hours of flight on the NCAR C130 aircraft during the Alliance Icing Research Study II in northeastern U.S. and southeastern Canada. Temperatures ranged from +5 to -45 °C; liquid water content (LWC) and ice content (IWC) were measured in concentrations below 1.25 and 0.45 g/m3 respectively. In addition, break-up of cloud particles due to impact at low velocity (terminal velocity) and with the aircraft instruments at high velocity was studied using data from convective and stratiform cloud particles replicated in formvar solution on the UND Citation aircraft (typical air speed 130 m/s) and video-recorded following impact on the NCAR C130 (typical air speed 130 m/s) and NASA DC-8 (typical air speed 200 m/s).;Measurements of electrical power were accomplished simultaneously every second to maintain near constant temperature during accretion and evaporation of only water on a cylindrical sensor and water and ice on a re-entrant sensor. Both sensors have identical collection efficiency. Liquid water content decreased as temperature decreased; ice content remained almost constant. The ratio of ice content to liquid water plus ice content showed a minimum value at -10°C and increased as temperature decreased. The ratio was at a minimum in the occurrence frequency between 0.1 and 0.9 throughout the range of temperatures. Liquid, glaciated and mixed-phase regions alternated within clouds. Mixed-phase regions were narrow, extending for a few hundreds of meters and occasionally even less.;Particles with a surface energy to impacting kinetic energy ratio larger than 10 break during impact. Shape and preferred orientation of the crystal at the moment of impact determine break-up severity. Physical details of the impact determines the transformation of impacting kinetic energy: (1) converting to thermal energy through viscous dissipation of deforming liquid or displacing air, (2) creating new surfaces through water splash or ice break-up, (3) forming dislocations or melt part of the crystal, or (4) retained by bouncing particles.;These conclusions are of major operational importance for the characterization of ice in the atmosphere, instrument collection efficiency, validation of remote sensing, and prediction of precipitation and electrification, and have implications for aircraft icing and forecasting.