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Polar tropospheric cloud microphysics, the Antarctic point of view
Constantino Listowski
Jeudi 07/02/2019, 11:00-12:00
Bât. 714, P. 1129, LSCE Orme des Merisiers

One of the greatest challenges in atmospheric models is the correct simulation of supercooled liquid water (SLW) in clouds, and more particularly of the relative amounts of SLW and ice in mixed-phase clouds (MPCs). In the polar regions these clouds are ubiquitous. Our understanding of the underlying processes leading to their formation is incomplete and the observations keep challenging our ability to model them. This is problematic given the strong impact of MPCs on the surface radiative budget, and the known polar amplification through which the Antarctic and the Arctic are undergoing stronger warming than anywhere else on Earth. In the Southern Ocean, down to the Antarctic coasts, climate models display significant biases in the net cloud radiative effect, and this traces back to their inability to correctly account for SLW. One reason for this is our poor understanding of cloud-aerosol interactions in the remote Antarctic region where marine aerosols play a key role in MPC formation. More generally, cloud turbulence, liquid to ice conversion via primary or secondary ice production, coupling with the surface via heat and moisture fluxes make the simulation of SLW and MPCs challenging. Contrary to the Arctic where anthropogenic pollution and continental aerosols complicate aerosol-cloud interactions, the Antarctic can be seen as a natural laboratory with pre-industrial conditions where key polar-specific processes can be studied, which involve interactions with sea ice, and marine aerosols - whether mineral or biogenic. We will present observations of SLW and MPCs as well as cloud modelling results in the Antarctic. On one hand we will explain how aircraft in-situ observations allow us to point at critical microphysical processes taking place in these clouds and to investigate the links with the surrounding environment and – on the other hand - why satellites and more particularly radar and lidar observations are necessary to constraint their microphysical properties Antarctic-wide, backed up by ground-based observations. Modelling results will be presented to highlight the standing issues in capturing the occurrences of polar MPCs as well as their liquid and ice contents, and the remaining mysteries about the actual sources of the cloud condensation nuclei and the ice nucleating particles responsible for their formation. Overall this has important consequences regarding the current efforts to correctly model the surface energy balance and the surface ice mass balance in the polar regions.

Contact : Juliette Lathiere
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