MICROphysicS of COnvective PrEcipitation (MICROSCOPE)

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This project will improve predictions of severe convective rainfall by addressing the problem of the microphysicsof precipitation in convective clouds. For the first time, study of the microphysics is embedded in aproject that includes the larger-scale dynamics of convective clouds, as part of the COnvective PrecipitationExperiment (COPE). COPE will connect this microphysical study with the system-scale dynamics of severeconvective UK weather events. COPE will also provide a programme of weather-system modelling, which willbring the microphysical understanding through to the improved prediction of rainfall at the weather-system, orcatchment scale.Weather forecast models are now run at resolutions of 1.5 km, which has helped to improve the predictionof the location and timing of convection. However, quantitative precipitation forecasts are still often poor ashighlighted in the Boscastle event (Golding et al., 2005). This is due in part to the lack of knowledge about thenucleation of ice particles in convective clouds, the warm rain process, and the rates of production of secondaryice particles and the subsequent growth of precipitation particles. However, high local accumulations were theresult of both intensity (microphysics of precipitation) and duration (organisation of and interaction between cellsalong the convergence line) of precipitation. The latter issue and wider-scale problem will be addressed in otherparts of COPE.There are two key parts to MICROSCOPE. The first concerns a fundamental problem: how do ice particlesform in clouds as a result of ice nuclei (IN), particularly at high temperatures? The second concerns precipitation:how do precipitation particles form and what are the rates of production and development? MICROSCOPE willaddress the challenge of explaining the production of primary ice particles in cumulus clouds, in the followingways.* We will make measurements of the properties of the aerosol particles, particularly soils and biologicalmaterial, on the ground and in the boundary-layer with the FAAM 146 aircraft.* Measurements will be made of the evolution of the droplet size distribution, the possible presence ofsupercooled raindrops and the formation of the first ice particles with carefully-guided penetrations of theaircraft that has been equipped with new instruments that can detect and characterise small ice particlesunambiguously (SID, 2DS, CAS-DPOL).* The dual-polarisation, Doppler radars will provide measurements of the location and time of the first precipitationechoes, the air motions and the types of particles.In order to explain the production and development of precipitation, process model and NWP model resultswill be compared to observations of the entrainment process, the development of the warm rain process, thegrowth of ice particles into precipitation particles by diffusional growth, the freezing of raindrops into graupelparticles, multiplication by secondary production processes, and riming. The comparisons will be achieved bymaking multiple penetrations at increasing altitudes measuring the particle size distributions in space and timeas well as the thermodynamics and dynamics of the cloud, and by obtaining information about the particles andthe rate of increase of the reflectivity echo from the dual-polarisation radar.The final step of MICROSCOPE, that will be led by the Met Office, is to incorporate the new information intoNWP models and to test against the data gathered during the project.