73°

Fog

Chris Bretherton (University of Washington),Boundary layer clouds and aerosols over the Southern Ocean: New observations for making better climate models.

February 20, 2019 3:30pm
MSA 7124

ABSTRACT

The Southern Ocean is stormy, cloudy and remote.  Global climate models typically simulate too little cloud in the cold sector of the extratropical cyclones that constantly sweep across it and struggle with their microphysics, with regional and global consequences for our changing climate.  Recent field and modeling studies are enriching our understanding of these processes and biases.  During 2016-2018, the U. S. and Australia jointly coordinated four campaigns studying cloud, aerosol, and ocean surface processes between Tasmania and Antarctica.  Cruises of a research ship gave a holistic view of the upper ocean and lower atmosphere during two summers; an island station provided year-round measurements, an icebreaker sampled down to the Antarctic coast, and a research aircraft sampled the clouds.  Intriguing early results include a surprisingly high concentration of small sulfate aerosol particles, an extreme lack of ice nuclei, prevalence of high-albedo multilayer supercooled liquid clouds at temperatures as low as -30 C, lightly precipitating ice and even drizzle,  and relatively high cloud droplet number concentrations much of the time.  Two climate models nudged to real temperature and wind fields were sampled at the same places and times as these observations. With realistic meteorology, they position the cloud layers reasonably but compare much less well with observed profiles of aerosols, liquid, ice and precipitation.