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C308: Impact of sea ice sourced sea-salt aerosols on Southern Ocean climate (Lead Supervisor: Xin Yang, British Antarctic Survey)

Supervisors: Xin Yang (British Antarctic Survey), Eric Wolff (Earth Sciences), Jeff Ridley (the Met Office), Anna Jones (British Antarctic Survey)

Importance of the area of research:

The Southern Ocean plays an important role in the earth’s climate. Current climate models, including the UK Earth System Model (UKESM), generally reflect too little solar radiation over the Southern Ocean, resulting in substantial shortwave radiation bias,  e.g. a ~3°C warmer sea surface temperature (SST) over the SO [i, ii].  This short-wave bias can lead to bias in the locations of the southern hemisphere jet and southern hemisphere tropical rain band. It also affects thermocline strength in coupled climate models and ocean mixing layer depth.The origin of the short-wave bias is not fully understood. The parameterisation of clouds has been suggested as a major reason for the poor representations of model clouds. Additional cloud condensation nuclei (CCN) and Ice Nuclei (IN) would increase cloud top albedo, thereby leading to the reflection of more sunlight and a cooling at the surface. This project will focus on the newly identified sea-salt aerosol source over sea ice [iii], which has not been included in any of the current climate models, and investigate its climate impact.

Project summary:

This project will use the Met Office UKESM to investigate the potential of the newly identified sea salt aerosols from sea ice zone to act as Cloud Condensation Nuclei (CCN) and Ice Nuclei (IN) and evaluate their climate-impact over the Southern Ocean. This project is a joint research between University of Cambridge, the Met Office and British Antarctic Survey, with aim of reducing the large SST bias over the Southern Ocean in UKESM. Focus will be on the sea ice sourced SSA parameterizations and their effect on cloud properties, precipitation and shortwave cloud forcing over the Southern Ocean.

What the student will do:

A successful candidate is expected to implement an updated scheme of the newly identified sea salt aerosol source to the chemistry and aerosol mode (UKCA-GLOMAP) of UKESM. Its effect on seasonal shortwave radiation will be evaluated against satellite data. The impact of the new aerosol source on the climatology, such as cloud microphysics and large scale dynamics (e.g. cyclone development, location of the southern hemisphere jet and sea surface temperature), will be assessed. A sensitivity study will be conducted, within the parameters of the sea salt scheme (a model ensemble), to understand the associated uncertainty.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

[i] Flato et al., 2013: Evaluation of Climate Models. In: Climate change 2013: the Physical Science Basis. Contribution of Working group I to the Fifth Assessment Report of the IPCC.

[ii] Bodas-Salcedo, A., Williams, K.D., Field, P.R., and Lock, A. P., 2012: The Surface Downwelling Solar Radiation Surplus over the Southern Ocean in the Met Office Model: The Role of Midlatitude Cyclone Clouds. J. Climate, 25, 7467–7486.  doi: doi.org/10.1175/JCLI-D-11-00702.1.

[iii]Yang, X, Pyle, J. A., and Cox, R.A., 2008: Sea salt aerosol production and bromine release: Role of snow on sea ice. Geophys. Res. Let., 35, L16815, doi:10.1029/2008GL034536.

 Follow this link to find out about applying for this project.

 

 

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