Karlsruhe's Institute of Technology, Freie Universität Berlin and the University of Geneva set out to determine whether and how far laser light and plasma can influence cloud formation.

For their investigations, the researchers used the facility AIDA (Aerosol Interactions and Dynamics in the Atmosphere) on KIT's Campus North and the mobile laser lab "Teramobile" developed in Geneva and Berlin. AIDA offers unique possibilities of studying aerosol and cloud processes under atmospheric conditions and can simulate all temperature and pressure conditions occurring in the lower and middle atmosphere.

 The "Teramobile" generates high-intensity laser light pulses. Unlike normal laser light, these pulses propagate in a specific way in the atmosphere. "Due to nonlinear optical effects, these laser pulses kind of produce their own light guides, thus remaining sharply focused over long distances even if they would normally be dissipated by airborne particles and atmospheric opacity," explains KIT's Institute for Meteorology and Climate Research – Atmospheric Aerosol Research (IMK-AAF) Professor Thomas Leisner. A current-conducting plasma channel forms as the air gets ionized along the laser beam. 

At the AIDA facility on KIT's Campus North, researchers investigate aerosol and cloud processes under atmospheric conditions. Photo: Markus Breig, KIT

Effects of plasma channels on ice formation or precipitation processes could not be proved in typical storm clouds, where ice crystals and sub-cooled water droplets coexist. In high cirrus clouds, which consist purely of ice crystals, the researchers, however, came across a surprisingly strong reaction to laser irradiation: As described in their PNAS paper, the laser pulses increase the number of ice particles by up to a factor of 100 within only a few seconds.

The fact that the optical density of the cirrostratus clouds is intensified by up to three orders of magnitude makes the clouds look much brighter. "The effect exerted on a typical thin sheet of cirrostratus clouds can be imagined to resemble laser-written contrails," Leisner says.

According to Leisner, however, this laser effect on the atmosphere presently can only be applied in scientific cloud research. "Until clouds can be manipulated from the ground," the KIT climate researcher explains "much progress is required in laser technology."