Cloud physics and aerosol research

Aerosol are small particles that have a wide range of important impacts on the atmosphere; they interact with solar and terrestrial radiation to perturb the Earth's energy budget; they play a key role in determining cloud properties; and in high concentrations they degrade air quality and visibility. Aerosol particles undergo complex atmospheric life-cycles and exhibit a vast range of properties, making their accurate representation in numerical models used for weather, climate and air quality prediction a significant challenge.

Clouds form and evolve through the interaction of a range of physical processes. Dynamical processes modulated by radiative heating and cooling lead to the lifting of air parcels and the condensation of water vapour. Cloud droplets and ice crystals form on pre-existing aerosol nuclei and may subsequently grow to form precipitation.

We study these processes using a range of instrumentation that is flown on board the FAAM BAe146 research aircraft.

We operate a range of advanced aerosol and cloud instrumentation on the aircraft including aerosol scattering, absorption, extinction and hygroscopicity instruments, optical particle counters, spectral radiometers and an aerosol backscatter LIDAR. The particle counters span the size range 0.1 to several thousand micrometres (0.0001 to several millimetres). These probes use the scattering of laser light from single particles and imaging techniques, both of which can give information on the size and phase (liquid or ice) of the particles. We have improved techniques to measure the bulk ice water content of cold clouds. This can vary by three orders of magnitude between convective clouds in the lower troposphere and cirrus in the upper troposphere.

Much of our research is focused on major international observing campaigns. These are often joint ventures with the UK and international academic groups. We work closely with colleagues in the Atmospheric Processes and Parametrizations group, from UK universities including Leeds and Manchester and also internationally to provide guidance on the improved representation of cloud and precipitation processes in the Unified Model.

Key aims

• Improved understanding of microphysical processes in cloud and precipitation systems.
• Guidance on the development of improved parametrization schemes for microphysical processes in the Unified Model.
• Development of improved observational techniques to study microphysical processes and bulk cloud properties.
• To measure the physical and optical properties of atmospheric aerosols.
• To determine the impact of aerosols on atmospheric radiation, visibility, cloud microphysics and air quality.
• To support development and testing of aerosol modelling within the Met Office and the UK academic community.
• To develop state-of-the-art instrumentation for aerosol measurement.

Current projects

• Arctic Cold Air Outbreak experiment - A field campaign based in Kiruna, Sweden, that will examine key processes that control the development and evolution of mixed-phase clouds (those that contain both ice and supercooled liquid water) in cold-air outbreaks.
• INC – Development of a new custom-built aircraft instrument for in situ characterisation of ice nucleating particles (INP) using a continuous flow diffusion chamber. The instrument will provide high quality measurements needed to test the representation of INP on ice cloud formation in Met Office NWP and climate models.