The tests of IN seeding materials used in Iran for cloud seeding (PV-26) and introduction of a cloud chamber


Ph.D. in Physics, Research Staff of National Research Center for Cloud Seeding, Yazd, Iran


The aim of this research is to report the results of testing of the PV-26 pyro-techniques materials and to report the operating conditions of a cloud and an aerosol chambers and also to introduce and describe these chambers of National Research Center of Cloud Seeding in Iran for further researches. The effect of ice nuclei produced by PV-26 pyro-techniques on artificial clouds has been surveyed under laboratory conditions. These tests show that this materials cause of increase the terminal velocities of ice crystals by  using an exponential fit, and by  using a linear fit. Also having captured using a microscope, the vivid photographs of ice crystals which, in the temperature  and 
the relative humidity less than 95%, had grown to the size of about , prove the reliability of the cloud chamber for scientific research. More than 54% of crystals have been greater than 20 microns and fit well in Magono-Lee classification.
Numerous tests have been performed to examine the toleration of chambers (especially, the more complicated one, cloud chamber) in extreme conditions and also to examine the capability of cloud chamber to produce reliable data. The results of these tests show that the gradient of the temperature in cloud chamber which is equipped with four temperature, one humidity and one pressure sensor, has a reasonable span. These testes are still being carried out.
In case of cloud chamber, the temperature could be varied from temperature of the environment to, the pressure, from pressure of environment to  below that, and the humidity, from humidity of environment to the maximum value that environmental conditions allow. Both of the chambers have centrifugal pump and filters to clean their internal air from background aerosols. The cloud chamber has an extra pump to keep the inside pressure at the desired value (Langsdorf, 1939; Donnan & wright, 1969). This chamber also has four thermometers to control the chiller compressors and monitor the gradient of the temperature.
At the present, the laboratory is equipped with two separate measurement tools. One of them consist a (Helium-Neon) laser and a digital detector for visible light which measures the intensity of the laser beam (Wagner et al., 2009). This system works like a turbidimeter and measures the transparency inside the cloud chamber. Having had a greater terminal velocity, bigger ice crystals precipitate faster and leave the internal space of cloud chamber for laser beam to pass (Heymsfield 1972, Heymsfield & Kajikawa 1987). When all other quantities are constant, the time interval in which the clarity of the cloud returns to the value corresponding to empty chamber, could be a criterion of the size of ice crystals (Wagner et al., 2006).
The other measurement system consists of an optical microscope and a special chemical gel to inscribe the shape of the crystals. The number of crystals and their shapes could be varied with respect to the physical circumstances like temperature, pressure, the number and type of the aerosols, etc (Mitchell et al., 1990). Although we know the ingredients of this gel, its suitable usage seems to be hard to achieve and there are still difficulties to make it practical. I will give more details in section 5. According to the Magono-Lee classification of natural snow crystals (Magono and Chung 1966), in these experiments, P1b, P1c, C1h and CP1c made the major portion amongst other crystals.