title: Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo.
abstract: Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties-ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration N d of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed N d. Enhanced N d is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in N d is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35(o) to 45(o)S) and by organic matter in sea spray aerosol at higher latitudes (45(o) to 55(o)S). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m(-2) over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere.
authors.affiliation: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195-1640, USA.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: McCoy
authors.affiliation: Atmospheric Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Susannah M
authors.initials: SM
authors.lastname: Burrows
authors.affiliation: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195-1640, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Wood
authors.affiliation: School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Grosvenor
authors.affiliation: Climate Ocean Sea Ice Modeling team, Computational Physics and Methods group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Elliott
authors.affiliation: Atmospheric Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Po-Lun
authors.initials: PL
authors.lastname: Ma
authors.affiliation: Atmospheric Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Rasch
authors.affiliation: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195-1640, USA.
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Hartmann
keywords: Atmospheric science; Climate; Southern Ocean; aerosols; albedo; clouds; sea spray; weather