Laser pulses can initiate artificial precipitation
Physicists from Germany, Switzerland and France have shown that exposure to high-power laser promotes condensation of water vapor in the atmosphere.
A relatively well-studied method for initiating precipitation is the so-called seeding clouds – delivery into the atmosphere of particles of any substance (most often silver iodide is used), which should serve as condensation nuclei. However, meteorologists still cannot give an accurate assessment of the effectiveness of this technique; some scientists also point to the possibility of a negative effect of silver iodide particles on the environment and human and animal health.
The new technology, which is absolutely environmentally friendly, has been tested using a Teramobile IR laser capable of delivering 100 fs pulses (10-13 s) and a power of 5 TW. In 2008, researchers experimented with this setup, aiming a beam at thunderclouds and causing electrical discharges.
The laser, the authors explain, ionizes nitrogen and oxygen molecules in the air, creating a kind of plasma channel, and the resulting molecular ions can become natural condensation nuclei. In order to evaluate the effect of the exposure, the scientists turned on a second laser of standard power and observed backscattering of radiation, which becomes more pronounced when more droplets are formed.
The experiments were carried out both in laboratory conditions (in a condensation chamber) and in nature. In the laboratory, immediately after the passage of the pulse along the plasma channel, droplets with a diameter of about 50 μm were formed, which united within three seconds and grew up to 80 μm. Under natural conditions with high humidity, physicists have also been able to register an increase in backscattering after impulses have been applied.
The technology is now at an early stage of development. “Of course, as long as we can only initiate condensation along the plasma channel, and we will not be able to cause rain,” admits study participant Jérôme Kasparian from the University of Geneva.
Research colleagues are skeptical about the prospects of the new technique. Thus, Bill Cotton (Bill Cotton) from the University of Colorado (USA) calls the results “intriguing”, but argues that the technology will most likely never seriously affect the formation of clouds and precipitation. In experiments with a condensing chamber, Mr. Cotton notes, the relative humidity of the air reached 230%, while in the atmosphere it rarely rises above 100%.