M.I.C.C - Manchester Ice Cloud Chamber
The new cold room facility in the Simon Building of The University of Manchester houses one of the tallest cloud chambers in Europe at a height of 10 m. The 1 m diameter fall tube spans 3 floors and can reach temperatures as low as -55°C. The chamber can also be pressure sealed and evacuated to simulate conditions found in the upper troposphere. Liquid water, mixed phase, or entirely glaciated clouds can be generated in the chamber, with cloud liquid water contents ranging from zero to the highest values found in nature being reproducible.
Water clouds are typically generated in two main ways. Most commonly, a water boiler is situated at the base of the chamber and boils to produce a cloud of droplets. At sub-zero temperatures, these become supercooled. It is also possible to use atomisers to generate a cloud of water droplets. Alternatively, a high power pump is used to rapidly evacuate the chamber, and the expansion of chamber air from ambient sources heterogeneously generates a cloud.
Ice clouds can be formed from clouds of supercooled liquid water droplets by either heterogeneously or homogeneously nucleating clouds. Homogeneous cloud nucleation when warmer than -40°C is achieved using one of two methods. Traditionally, a liquid nitrogen-cooled rod (-200°C) is inserted into the cloud to cause nucleation. Alternatively, a compressor expansion technique is used in which a small volume of compressed air is adiabatically expanded to locally reduce air temperature below the homogeneous freezing temperature and force ice formation. The crystals generated then grow at the expense of the available water vapour and droplets. By varying the environmental chamber conditions and nucleation techniques, a range of habits, sizes and number concentrations of ice crystals can be produced for experimental studies. The large height associated with the new chamber provides a longer crystal fall and growth time, and a new opportunity to grow particularly large, mm-sized, ice crystals in experiments.
The chamber is also laced with sensors and probes. In addition to pressure and humidity detectors and a network of temperature sensors, a number of inlets and port holes into the chamber allow the insertion of cloud and aerosol sampling probes. The majority of the probes are located at the base of the cloud chamber and sample falling cloud hydrometeors. Manchester utilises two Cloud Particle Imaging probes (CPI) and a Cloud Droplet Probe (CDP) amongst others; both the CPIs and CDP have been used extensively in chamber studies to sample ice crystals and droplets. Also used in the chamber is a Welas aerosol detection probe.
Research in the chamber has covered several scientific topics, ranging from aggregation, ice crystal light scattering, nucleation, cloud microphysics, and thunderstorm electrification. More details about the results of the electrification studies can be found in the results section.
Summary of Key Features:
- The Manchester Ice Cloud Chamber (MICC) is a fall-tube 10 m tall and 1 m in diameter. It is one of the tallest such facilities in Europe.
- The chamber is located inside three cold rooms spanning three stories, and each can be independently set to reach temperatures as low as -55°C.
- The 10 m high fall tube can be separated into three independent chambers for some experiments.
- The chamber can be sealed and internal pressure reduced to 50 mbar to simulate upper tropospheric conditions.
- Port holes in the chamber walls allow instruments to be fed into the chamber at different heights and allow the clouds to be viewed from outside.
- A number of cloud measurement probes can be located at the base of the chamber and sample cloud as it falls through the many port holes.
Current Research Topics:
Dr. Christopher Emersic maintains his own M.I.C.C webpages describing the chamber and the results of chamber studies.