Mixed-phase clouds (MPCs) consist of liquid droplets and ice crystals, and their respective amounts influence the formation of precipitation, cloud lifetime, and electrification. At the same time, the cloud’s composition controls its radiative properties as liquid droplets and ice crystals have different scattering characteristics. For ice to form at temperatures above -38°C, a special subset of aerosol particles called ice-nucleating particles (INPs) are required.
In the Arctic, it is believed that the majority of INPs are either of local origin (marine, biological particles emitted from the ocean) or stem from terrestrial dust sources transported over long distances.
However, due to the sensitive balance between liquid and ice in Arctic MPCs, it is hard to predict how these clouds will respond to a warming climate: (1) the warmer temperatures could lead to a state with more liquid water and a higher albedo, thus limiting future warming (e.g., Bjordal et al., 2020); or (2) the retreating sea ice could expose new local sources of highly active marine biological INPs, ultimately leading to more ice crystals at warmer temperatures (e.g., Carlsen and David, 2022; Creamean et al., 2022). Therefore, to elucidate the complex and competing microphysical processes, we will investigate the differences in the composition of Arctic MPCs over sea ice and open ocean.
To this end, we will use observations from the ISLAS (Isotopic links to atmospheric water's sources) 2022 airborne campaign, including in situ (imaging probes of cloud water and ice) and remote sensing (cloud radar and lidar) data sets. The transition of MPCs from sea ice to the open ocean was investigated during dedicated research flights (see Fig. 1), thus providing a significant data set to understand the influence of the surface type on the MPCs in the Arctic.
The prospective candidate will gain invaluable experience in analyzing data from state-of-the-art airborne instrumentation. The candidate should have basic programming skills (Python is preferred) and an interest in Arctic clouds. The project will begin in the Fall of 2022 and there is the possibility to participate in a field campaign in the Norwegian Arctic in the Spring of 2023.
References:
- Bjordal et al. (2020): Equilibrium climate sensitivity above 5°C plausible due to state-dependent cloud feedback, https://doi.org/10.1038/s41561-020-00649-1
- Carlsen & David (2022): Spaceborne evidence that ice-nucleating particles influence high-latitude cloud phase, https://doi.org/10.1029/2022GL098041
- Creamean et al. (2022): Annual cycle observations of aerosols capable of ice formation in central Arctic clouds, https://doi.org/10.1038/s41467-022-31182-x
