Wednesday, 17 January 2007: 5:00 PM
Cloud seeding as a technique for studying aerosol-cloud Interactions in marine stratocumulus
207A (Henry B. Gonzalez Convention Center)
The response of the microphysical characteristics of marine stratocumulus clouds to aerosol perturbations was studied using hygroscopic flares burned in clouds observed off the coast of California in June 2006. These seeding experiments were designed to establish the feasibility of using this method for studying cloud-aerosol interactions in a relatively steady cloud environment. Aerosol, cloud and drizzle measurements for these experiments were made from the CIRPAS Twin Otter research aircraft, which in addition to its normal complement of aerosol and cloud physics probes was equipped with an FMCW 94 GHz radar for observing the fine structure of large-drop populations in the clouds seeded. To demonstrate this technique, we show results from a case study made in a stratocumulus cloud approximately 300 m thick with mean cloud droplet concentrations of about 200 cm-3. Magnesium/potassium perchlorate flares (manufactured by Ice Crystal Engineering) were burned cross-wind in the cloud to give two seeded lines ~ 8 km in length and about 1 km apart. In-cloud intersects of the flare plumes were made with the Twin Otter. Aerosols concentrations in the 0.1-0.3 micrometer range were found to give clear signatures of the plume crossings. For this case, 16 crossings were made during a 30 minute period and provided direct observations of the time evolution of the cloud and drizzle characteristics relative to the cloud background during this time. Results from the cloud evolution characterization, the merits of this approach, and potential for extending this technique for future applications will be discussed.