Cloud seeding as a technique for studying aerosol-cloud interactions in marine stratocumulus

[1] Giant hygroscopic aerosols were introduced into a solid marine stratocumulus cloud ( 200 m thick) by burning hygroscopic flares mounted on an aircraft. The cloud microphysical response in two parallel seeding plumes was observed using an instrumented aircraft making 16 transects of the plumes. The cloud drop size distribution width increased in the plumes due to an increased number of small cloud drops ( 3-5 mu m) on the earlier transects and a 5- fold increase in the number of large drops ( 20 - 40 mu m) relative to the background cloud 30 minutes later. The cloud effective diameter increased from about 11 mm in the background to 13 mm in the plumes. Although the giant nuclei were only a small fraction of the total aerosols produced by the flares, they dominated the cloud response. The merit of the seeding approach for controlled observational studies of aerosol- cloud interactions in marine stratocumulus was demonstrated.