Abstract. Climate predictions for the rapidly changing Arctic are
highly uncertain, largely due to a poor understanding of the processes
driving cloud properties. In particular, cloud fraction (CF) and cloud phase
(CP) have major impacts on energy budgets, but are poorly represented in most
models, often because of uncertainties in aerosol–cloud interactions. Here,
we use over 10 million satellite observations coupled with aerosol transport
model simulations to quantify large-scale microphysical effects of aerosols
on CF and CP over the Arctic Ocean during polar night, when direct and
semi-direct aerosol effects are minimal. Combustion aerosols over sea ice are
associated with very large (∼10 W m−2) differences in longwave
cloud radiative effects at the sea ice surface. However, co-varying
meteorological changes on factors such as CF likely explain the majority of
this signal. For example, combustion aerosols explain at most 40 % of the
CF differences between the full dataset and the clean-condition subset,
compared to between 57 % and 91 % of the differences that can be
predicted by co-varying meteorology. After normalizing for meteorological
regime, aerosol microphysical effects have small but significant impacts on
CF, CP, and precipitation frequency on an Arctic-wide scale. These effects
indicate that dominant aerosol–cloud microphysical mechanisms are related to
the relative fraction of liquid-containing clouds, with implications for a
warming Arctic.
Regularities of the variability of large-scale sea ice drift structures in the Arctic Ocean (based on satellite data 1978-2017)
