Aerosol-cloud interaction from aircraft observations in VOCALS
Authors
Peter Daum — Brookhaven National Laboratory
John Hubbe — Pacific Northwest National Laboratory
Larry Kleinman — Brookhaven National Laboratory
Jian Wang — Washington University in St. Louis
Yin-Nan Lee — Brookhaven National Laboratory
Gunnar I. Senum — Brookhaven National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Arthur J Sedlacek — Brookhaven National Laboratory
Category
Aerosol-Cloud-Radiation Interactions
Description
Comparison of cloud droplet number concentration with sub-cloud aerosol for the entire VOCALS campaign. Data points that are connected are sequential in time. Breaks appear because aircraft flight patterns consisted of transects and vertical profiles in and out of cloud.
During the VOCALS field campaign, the U.S. DOE G-1 aircraft was used to make cloud and aerosol measurements. Flight plans were designed so that cloud penetrations could be associated with pre-cloud (or sub-cloud) aerosol particles around which cloud droplets formed. This poster describes the aerosol size distributions and the relation between pre-cloud aerosol and cloud droplet number concentration.
Sub-cloud aerosol typically had an Aitken and accumulation mode separated by a Hoppel minimum at 70 to 90 nm. Sub-micron aerosol had an average composition of 1/4 neutralized H2SO4 (i.e. H1.5(NH4)0.5SO4) with a 10% admixture of organics that reflected large SO2 emission rates from smelters and power plants located near the coast of Chile. Aerosol with this composition is expected to be easily activated as confirmed by CCN measurements. At a supersaturation of 0.2%, particles with a diameter greater than ~ 100 nm are on average activated. Variations in aerosol composition were minor.
Cloud droplet number concentration (CDNC) as a function of below-cloud aerosol are shown in the attached figure. Results are within the range of values obtained at different locations by other investigators. Measurements of dried interstitial aerosol from a DMA and PCASP in the cabin and from a PCASP mounted outside of the aircraft indicate a significant fraction of large particles in the size range 150–300 nm. Partially dried cloud droplets appear at larger sizes in the nose-mounted PCASP. Mechanisms for the creation of a population of large hygroscopic interstitial particles are discussed.
