Characterising the response of OAP in-situ particle imagers: implications for cirrus observations

In-situ measurements of cloud particle size, habit and concentration provide insights into cloud radiative properties and key microphysical processes such as ice nucleation, crystal growth and precipitation. This presentation will discuss the uncertainties and artefacts associated with a widely used family of instrumentation in the field of cloud physics, optical array probes (OAPs). Using a combination of modelling and laboratory experiments we will show how these measurements can be improved and their uncertainties constrained. The impact of this on field measurements and our understanding of cirrus microphysics will be examined using measurements collected during the PICASSO project (Parameterizing Ice Clouds using Airborne obServationS and triple-frequency dOppler radar). The ongoing PICASSO project has to date performed 17 flights sampling deep ice clouds using a suite of instrumentation, which includes a variety of the most advanced optical array probes and also a holographic imaging probe. At the same time, collocated triple frequency observations were obtained with synchronized 3, 35 and 94GHz radars from the NERC Facility for Atmospheric and Radar Research (NFARR) at the Chilbolton Observatory. This presentation will show how improved in-situ measurements can be used to better constrain radar retrievals of ice microphysics.