The Influence of Local and Long-Range Transported Aerosol Particles on Arctic Mixed-Phase Clouds

Arctic low-level clouds often contain both ice and water. They are highly sensitive to microphysical processes, which can either sustain or break down the unstable mixed-phase state and thereby determine the longevity of the clouds and their radiative impact. The clouds are influenced by the availability of aerosol particles, which can act as ice nuclei (IN) or cloud condensation nuclei (CCN) and sometimes become the limiting factor for cloud formation. The aerosol concentration in the Arctic boundary layer is low compared to other regions. Potential sources include local marine aerosol emissions and long-range transport. The emission of local, marine aerosol particles is connected to open water and open leads (open water channels) in the pack ice. The transported aerosol types depend on the large-scale meteorology, i.e. on air mass transport. Currently it is not very well known what governs the Arctic background aerosol concentration and its variability. Therefore, it is important to quantify Arctic aerosol concentrations and the associated impact on cloud microphysics.

The aim of our study is to derive characteristic vertical profiles of CCN and IN for two different situations in the Arctic and investigate the influence on the cloud microphysics and the evolution of a mixed-phase Arctic boundary layer cloud. The two situations investigated represent two different source types of aerosols in the Arctic region. We compare a situation where the aerosol concentrations are either predominantly governed by local sources or dominated by long-range transport. In case of local sources the aerosol particles are emitted at the surface, while the transported aerosol particles are introduced above the boundary layer inversion. To compile the vertical profiles for different aerosol scenarios we use field measurements in combination with regional modeling using the regional model COSMO-ART (Vogel et al., 2009). The influence of the different vertical aerosol profiles on the cloud microphysics is investigated using the LES model MIMICA (Savre et al., 2014).

References

Vogel, B., Vogel, H., Bäumer, D., Bangert, M., Lundgren, K., Rinke, R., Stanelle, T. (2009), The comprehensive model system COSMO-ART - Radiative impact of aerosol on the state of the atmosphere on the regional scale, Atmos. Chem. Phys., 9, p. 8661-8680.

Savre, J., Ekman, A. M. L. and Svensson, G. (2014), Technical note: Introduction to MIMICA, a large-eddy simulation solver for cloudy planetary boundary layers, J. Adv. Model. Earth Syst., 6, p. 630–649.