Aircraft measurements to validate and improve numerical model parametrisations of ice to water ratios in clouds

Eleven flights of the C-130 of the Meteorological Research Flight, in several different cloud types and air masses, have been used to determine the ratio of the mass of ice to water in mixed phase clouds. Data from the Particle Measuring System Inc. (Boulder, CO, USA) (PMS) 2D probes on the aircraft have been analysed with an automatic technique for classifying cloud particle shapes. This technique and its limitations are described in detail. The results are used to validate and improve parametrisations of cloud glaciation processes used in the UK Meteorological Office General Circulation Model and the Mesoscale Model. In general it is found that parametrisations of the ratio of the mass of ice to water of particles greater than 125 mu m in a parcel of cloud based on the ambient air temperature are more realistic than those based on cloud top temperatures.