Artificial rainfall

When the droplets in a cloud are too small, or there is not proper environment to create enough ice crystals, we can use artificial ways to help small water drops grow larger, or create ice crystals. And thereby the formation of precipitation occurs. This is called artificial rainfall.

There are many ways to make rain. First, In a warm cloud, spraying hydrophilic substance like powder of sodium is one of the way to make artificial rainfall. Or spraying water drops that are similar to raindrops size can be one of the way, too. They let the water drops grow though collision and coalescence to finally become rain.

The most common way make rain in a cold cloud, is to use dry ice or silver iodide. Dry ice can reduce the temperature of near water droplets, since the temperature of dry ice is –78 °C. Therefore without ice-crystal nuclei, supercooled water droplets are transformed into ice crystals, which will eventually become rain. On the other hand, Silver iodide can act as a ice-crystal nucleus. Through the process of growing the ice crystals due to coexistence of water droplets, the rain will be formed.

In conclusion, spreading cloud seeds into the clouds will increase the probability and the amount of precipitation. And that is the basic idea of artificial rainfall. In general the artificial rainfall can be divided depending on how spread the substance that help to make raindrops. Ground rainmaking and aerial rainmaking.

1) Ground rainmaking

By using the instrument that is called ground rainmaker, a silver iodide solution burns so the particle of silver iodide float up to the sky with the smoke. And they will act as ice-crystal nuclei

2) Aerial rainmaking

By using an airplane, silver iodide or dry ice cloud seeds is spread. This method is more effective than ground rainmaking, because the cloud seeds spreaded can be delivered precisely to clouds with cold enough temperatures. But the problem is that using airplane is expensive.