- Graduate Position
This project investigates sea salt and ice nucleating particles (INP) in air and snow above sea ice to quantify a hitherto unknown particle source associated with blowing snow during storms and to assess implications for polar-region wide background aerosol, clouds and climate.
Importance of the area of research concerned:
Atmospheric aerosols represent the largest source of uncertainty in model predictions of global climate. Aerosols influence radiative forcing and thus climate because they alter the planetary albedo both directly by absorbing and scattering sunlight and indirectly by modifying clouds. Sunlit aerosols can also release reactive chemical trace gases, which alter significantly the concentration of atmospheric pollutants, such as tropospheric ozone. Sea salt aerosol (SSA) is a major component of the global natural background aerosol and originates mainly from the open ocean. Recent in situ observations confirmed that blowing salty snow above sea ice, which undergoes sublimation, releases SSA rivalling the open ocean source per surface area. Furthermore, a fraction of SSA from blowing snow may consist of cloud condensation nuclei (CCN) or ice nucleating particles (INPs), which can significantly influence occurrence and phase of low-level clouds. Thus, in order to make a step-change in improving climate models it is paramount to quantify magnitude and climate sensitivity of the new aerosol source.
Project summary :
The project main objectives are a) to quantify the contribution of sea salt aerosol (SSA) from sea ice sources (blowing snow, frost flowers, open leads) to ice nucleating particles (INP), and b) to assess the impact of this new INP source on regional clouds and climate. A first step is to measure INP concentrations in existing snow, ice core and aerosol filter samples from the polar regions. In a second step, these data will be used to develop a parameterisation of a sea ice source of INP. To do this the existing model mechanism for SSA production from blowing snow above sea ice will be refined by taking into account the spatial variability of physical and chemical properties of sea ice surfaces. And finally, the sensitivity of SSA and INP production from blowing snow and impacts on polar climate will be estimated under modern climate change scenarios using a global climate model.
What will the student do?:
In a first step, you will analyse in the laboratory with an established off-line technique existing snow, ice core and aerosol filter samples from the polar regions both North and South to determine respective concentrations of ice nucleating particles (INP). In second step, you will use these data to develop a model parameterisation of a potential INP sea ice source with a particular focus on the mechanism of SSA production from blowing snow. You will take into account spatial and temporal variability of sea ice surface properties (sea ice extent, lead fraction, snow depth & salinity) and constrain air mass origin using back trajectory modelling. And finally, you will apply the new parameterisation in a global climate model to estimate the sensitivity of SSA and INP production from sea ice and blowing snow at high latitudes and associated impacts on climate and air quality under climate change scenarios.
- References - references should provide further reading about the project:
Frey, M. M., Norris, S. J., Brooks, I. M., Anderson, P. S., Nishimura, K., Yang, X., Jones, A. E., Nerentorp Mastromonaco, M. G., Jones, D. H., & Wolff, E. W. 2020. First direct observation of sea salt aerosol production from blowing snow above sea ice. Atmos. Chem. Phys., vol. 20, pp. 2549–2578, doi:10.5194/acp-20-2549-2020
- Creamean, J.M., Barry, K., Hill, T.C.J. et al. 2022. Annual cycle observations of aerosols capable of ice formation in central Arctic clouds. Nat Commun 13, 3537, doi:10.1038/s41467-022-31182-x.
- Yang, X., Frey, M. M., Rhodes, R. H., Norris, S. J., Brooks, I. M., Anderson, P. S., Nishimura, K., Jones, A. E., & Wolff, E. W. 2019. Sea salt aerosol production via sublimating wind-blown saline snow particles over sea ice: parameterizations and relevant microphysical mechanisms, Atmos. Chem. Phys., vol. 19, pp. 8407–8424, doi:10.5194/acp-19-8407-2019.