Airborne Holographic Imaging Probe

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Clouds play a key role in understanding future climate change and their representation in global models represents the biggest uncertainty in predicting future climate change. Clouds containing the ice phase are among those about which least is known and as a result are the most poorly represented in climate models. Correct representation of these clouds in weather forecasting models is also very important. The concentration of aerosol particles in the atmosphere that can initiate the ice phase (ice forming nuclei) at temperatures slightly below 0C is small. The ice phase, once formed, very effectively converts cloud water into snow and hail. This falls from the cloud depleting it of water, leading to its break-up, as well as producing precipitation at the surface. The development of ice also has a marked influence on the interaction of the cloud with short wave radiation from the sun. This is because numerous small water droplets are partly replaced by fewer larger ice crystals with complex shapes. New measurements of the microphysics of the cloud are needed to improve the understanding and treatment of these issues in atmospheric models. Current instruments used on research aircraft have difficulty measuring small ice crystals associated with the origin of the ice phase. The way these interact with the cloud is often determined by their nearest neighbour water droplets and larger ice particles. At temperatures slightly below 0C (down to -20C) the shortage of ice-forming aerosols means that natural processes which lead to the multiplication (sometimes by several orders of magnitude) of the ice particles present are very important, and depend on the interactions between ice particles and other cloud particles present. This proposal is to acquire a new instrument, an Airborne Holographic Imaging Probe, which will give us the ability to simultaneously measure all the cloud particles, their shape, size and relative positions within its sample volume, at high resolution. In addition, these measurements will not suffer from many of the artefacts associated with other current measurement techniques. Key components of the new instrument will be constructed for us by the University of Mainz in Germany who developed the previous version of this probe. Other components will be purchased from the same suppliers as used by the University of Mainz to maintain compatibility with their tried and tested system. However we will construct an instrument with a faster camera and a larger sample volume to more reliably detect the position of small ice crystals and their relative position in the cloud, as well as measuring their size distribution and shape. This instrument will then be installed and flown on the UK community research aircraft, the FAAM BAE 146, to provide this improved capability to the UK cloud science community. We already operate a range of other probes to measure larger ice particles, water droplets and precipitation on this and other aircraft. With this new instrument we will make a significant step forward in our cloud microphysics measurement capability and understanding, bridging an important gap by providing new and improved data that can be made available to those developing climate and weather forecasting models.