Direct Evidence of Reduction of Cloud Water after Spreading Diatomite Particles in Stratus Clouds in Beijing, China

Artificial weather modification experiments have been intensively practiced in many years over China, and some progresses have been made, including more methodologies and advanced instruments. However, a challenge question still remains for providing convincing scientific evidence during these practices and experiments. This is a very difficult scientific issue, which is related to complicated cloud physical science, such as to accurately predict the large natural variability of cloud formation and precipitation. In this study, we report a clear evidence that the cloud water is reduced after spreading diatomite particles in stratus clouds during a field experiment in Beijing, China. The analysis shows that the diatomite particles (15–20？ m in radius) are large and have strong hygroscopic property (absorbing cloud water). As a result, during the experiment, spreading large diatomite particles lead to downward motion (producing more stable atmospheric condition) and reduction of cloud water. It is noted that due to lacks of instruments, this designed experiment only can provide a qualitative result (such as photo evidence), and no quantitative result can be drawn from this experiment. 1. Introduction and Methods The theory and experiment for artificial weather modifications have a long history. The artificial weather modifications include to enhance or to reduce cloud formation and precipitation. The early experiments for artificial reduction of precipitation occurred in early 1940s. For example, Langmuir and his colleagues discovered that silver iodide (AgI) had nucleating ability to cause a rapid conversion of the water to ice, leading quickly to the production of snowflakes and the dissipation of cloud in the seeded region. Since then, AgI is widely used in cloud seeding process. In a general case, increase in numbers of cloud condensation nuclei (CCN) leads to enhancement of cloud formation and precipitation. However, if the numbers of CCN exceed a certain amount in clouds (overspread), with a limited amount of water contents available in clouds, a large amount of small cloud particles is formed to inhibit the formation of large rain droplets. Instead of enhancement of precipitation, the overspreading AgI particle is often considered as artificial reduction of precipitation. Li et al. [1] used a state-of-the-art dynamical model, Weather Real time Forecast (WRF), coupled with a detailed cloud micro-physical model to quantify the relationship between CCN and precipitation. Their result illustrated that there is a threshold CCN value for whether the