In-situ airborne observations by the FAAM BAE-146 aircraft for CONSTRAIN - Cold Cloud Microphysical Parameterisation Studies.

The main issues are the pristine ice number concentration, snow evolution leading to surface precipitation, mixed-phase and cold cloud length scales. The main goals in order of priority are

- to provide statistical datasets to act as a critical holistic test of three phase microphysics as RICO did for warm cloud microphysics (e.g. cold air outbreak). - to test whether the background aerosol concentration active as ice nuclei can be used to predict the pristine ice concentration in cases where there is limited ice multiplication.

- to test detailed microphysical assumptions in model, which include capacitance, aggregation efficiency vs temperature (conversion rate from 'ice' to 'snow' categories), mass-dimension relations and area-dimension relations (these combine to give fall-speed).

- To investigate small ice (sub 100 microns) concentration controversy.

The project aimed to conduct studies of water vapour, ice crystal habit, turbulence and radiative properties of contrail as it either spreads into cirrus or dissipates. Boundary conditions for LEM studies of contrail lifecycles were delivered and Measurements of radiative forcing from spreading contrail were taken for comparison to other cases. Case studies for testing later contrail cirrus parameterization in the Unified Model were also be considered.