Publication Date:
2018-01-09
Description:
We compared star-photometry-derived, polar winter
aerosol optical depths (AODs), acquired at Eureka,
Nunavut, Canada, and Ny-Ålesund, Svalbard, with GEOSChem
(GC) simulations as well as ground-based lidar and
CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization)
retrievals over a sampling period of two polar winters.
The results indicate significant cloud and/or low-altitude
ice crystal (LIC) contamination which is only partially corrected
using temporal cloud screening. Spatially homogeneous
clouds and LICs that remain after temporal cloud
screening represent an inevitable systematic error in the estimation
of AOD: this error was estimated to vary from 78 to
210% at Eureka and from 2 to 157% at Ny-Ålesund. Lidar
analysis indicated that LICs appeared to have a disproportionately
large influence on the homogeneous coarse-mode
optical depths that escape temporal cloud screening. In principle,
spectral cloud screening (to yield fine-mode or submicron
AODs) reduces pre-cloud-screened AODs to the aerosol
contribution if one assumes that coarse-mode (super-micron)
aerosols are a minor part of the AOD. Large, low-frequency
differences between these retrieved values and their GC analogue
appeared to be often linked to strong, spatially extensive
planetary boundary layer events whose presence at either
site was inferred from CALIOP profiles. These events
were either not captured or significantly underestimated by
the GC simulations. High-frequency AOD variations of GC
fine-mode aerosols at Ny-Ålesund were attributed to sea
salt, while low-frequency GC variations at Eureka and NyÅlesund
were attributable to sulfates. CALIOP profiles and
AODs were invaluable as spatial and temporal redundancy
support (or, alternatively, as insightful points of contention)
for star photometry retrievals and GC estimates of AOD.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf