Spatiotemporal variations in summertime Arctic aerosol optical depth
caused by synoptic-scale atmospheric circulation in three reanalyses
Abstract
Atmospheric aerosols influence the radiation budget, cloud amount, cloud
properties, and surface albedos of sea ice and snow over the Arctic. In
spite of their climatic importance, Arctic aerosol contains large
uncertainties due to limited observations. This study evaluates the
Arctic aerosol variability in three reanalyses, JRAero, CAMSRA, and
MERRA2, in terms of the aerosol optical depth (AOD), and its
relationship to the atmospheric disturbances on synoptic timescales. The
AOD becomes highest in July–August over most of the Arctic regions,
except for the North Atlantic and Greenland, where monthly variability
is rather small. The three reanalyses show a general consistency in the
horizontal distribution and temporal variability of the total AOD in
summer. In contrast, the contributions of individual aerosol species to
the total AOD are quite different among the reanalyses. Compared with
observations, the AOD variability is represented well in all reanalyses
in summer with high correlation coefficients, albeit exhibiting errors
as large as the average AOD. The composite analysis shows that large
aerosol emissions in Northern Eurasia and Alaska and transport by a
typical atmospheric circulation pattern contribute to the high aerosol
loading events in each area of the Arctic. Meanwhile, the empirical
orthogonal function analysis depicts that the first- and second-largest
AOD variabilities on the synoptic timescales appear over Northern
Eurasia. Our results indicate that these summertime AOD variabilities
mainly result from aerosol transportation and deposition due to the
atmospheric disturbances on synoptic scales, suggesting an essential
role played by Arctic cyclones.