Cloud clearing with a CO(2) laser in a cirrus cloud simulation facility.

We report experiments that confirm our prediction that clouds consisting of ice crystals with properties similar to those of cirrus clouds can be cleared with relatively low pulsed CO(2) laser energy density and that the cleared channel is resistant to obscuration by recondensation of the evaporated water. For the experiments reported here, we use a unique cloud-generating apparatus consisting of a low-speed wind tunnel with water spray injectors to generate water droplets or, with ice nucleus seeding at low temperatures, ice crystals. The air temperature can be controlled over the range of ambient to -40 degrees C. A significant clearing of ice crystal clouds was observed with pulsed CO(2) laser fluence in the range 0.2 to 1.5 J/cm(2) and, as expected, recondensation was found to depend on ice particle mass concentration. At ice particle concentrations similar to those found in cirrus clouds, recondensation did not occur.