Developing and Testing of an Expansion Cloud Chamber for Cloud Physics Research

The expansion cloud chamber is an important equipment for the research on nucleation process and mechanism of aerosol and weather modification seeding agents. It provides experimental conditions, in which the vapor can transform to water or ice super saturated. But for a long time, expansion cloud chamber with advanced cloud particle spectrum and image measurement system is absent in China. A independently developed expansion cloud chamber is established recently to investigate cloud physical and chemical processes. It consists of cloud chamber equipment, environmental and cloud physics parameter measurement systems, data communication systems and control system.The cloud chamber system mainly includes an experimental reaction chamber and a pre-vacuum tank, and adopts the split design. They are connected through controllable valves. The inside capacity of the experimental reaction chamber and pre-vacuum tank are 1.5 m³ and 9 m³, respectively. The control target air pressure of the reaction chamber is 100 hPa, and that of the pre-vacuum tank is 30 hPa. The cloud chamber system is equipped with advanced measuring instruments, such as environmental parameter detectors, cloud particle spectrometer, the precipitation particle spectra instrument, cloud particle imager, visibility meter, aerosol particle spectrometer, high speed camera system, etc.It is the first time that the chamber system uses domestic cloud particle spectrometer and imager measurement system. Tests show that the cloud chamber system has good temperature and pressure controlling ability. The average cooling rate can reach 0.26℃·min^-1 and temperature distribution in cloud chamber is uniform. In the chamber, the fog formed by expansion process lasts 4 minutes. The maximum concentration of fog droplets reaches 6.1 cm^-3, the droplet spectrum range is 3-8 μm, and the average effective diameter is about 6.5 μm. At the same time, clear fog droplet images can be obtained by high speed camera. It can control the low-temperature environment from room temperature to -50℃, and achieve pressure expansion cloud simulation and microphysical parameter monitoring. The lack of indoor experimental equipment for aerosols and warm cloud seeding agents will be solved. It has important significance for verification of nuclear properties of warm cloud seeding agents and improving the technology of warm cloud precipitation enhancement.