The Microphysical and Radiative Interactions of Arctic Multilayer Clouds

Multilayer clouds have been found to occur frequently in the Arctic, as determined by ship-based campaigns. Nevertheless, they remain underrepresented in the literature compared to their single-layer counterpart. To deepen our understanding of these clouds regarding microphysics and radiative processes, and to estimate the frequency of occurrence of such phenomena in the Arctic region, we utilise the numerical weather prediction model ICON. 

The model domain, encompassing 71°N-90°N, has been initialised using analysis data from ICON Global and 32 consecutive 24-hour simulations were conducted at a 2.5km grid spacing. The multilayer clouds studied here occurred during the Arctic MOSAiC campaign, active during 2019-2020. The season with the highest number of multilayer clouds, as determined by an observational algorithm, was selected: namely, early autumn (August to September 2020). Model output was acquired at a high temporal resolution following the MOSAiC drifting site and includes full regional coverage of cloud hydrometeors and radiative products. To enhance the representation of Arctic ice nucleating particles (INP), a new immersion freezing parameterisation has been developed, underpinned by extensive Arctic campaigns and station data across the Arctic sector. 

Here, we will present modelled multilayer clouds across the Arctic sector, highlighting a high occurrence of such clouds in the region. We further investigate their microphysical and radiative properties in comparison to single-layer clouds. Using observational products from the MOSAiC campaign for comparison, we further strengthen our modelled understanding of these clouds. Our findings indicate that multilayer clouds differ significantly from single-layer clouds due to both microphysical and radiative interactions. In terms of microphysics, the seeder-feeder mechanism, whereupon frozen precipitation may act as a seed for ice formation in a lower cloud layer, is prevalent, impacting the cloud phase, precipitation and the formation of new cloud particles. In terms of radiative processes, multilayer clouds have been found to have a substantial radiative impact. The presence of upper clouds may efficiently reduce the cloud-top radiative cooling of lower cloud layers, impacting macrophysical cloud properties. Furthermore, we will demonstrate that multilayer clouds exert a surface radiation budget impact that is twice that of single-layer clouds. This emphasises the necessity for further investigation into these cloud systems in this rapidly changing region.