In this study we investigate to what degree it is possible to reconcilecontinuously recorded particle light extinction coefficients derived from dryin situ measurements at Zeppelin station (78.92° N,11.85° E; 475 m above sea level), Ny-Ålesund, Svalbard, thatare recalculated to ambient relative humidity, as well as simultaneousambient observations with the Cloud-Aerosol Lidar with OrthogonalPolarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared PathfinderSatellite Observations (CALIPSO) satellite. To our knowledge, this representsthe first study that compares spaceborne lidar measurements to opticalaerosol properties from short-term in situ observations (averaged over 5 h)on a case-by-case basis. Finding suitable comparison cases requires anelaborate screening and matching of the CALIOP data with respect to thelocation of Zeppelin station as well as the selection of temporal and spatialaveraging intervals for both the ground-based and spaceborne observations.Reliable reconciliation of these data cannot be achieved with theclosest-approach method, which is often used in matching CALIOP observationsto those taken at ground sites. This is due to the transport pathways of theair parcels that were sampled. The use of trajectories allowed us toestablish a connection between spaceborne and ground-based observations for57 individual overpasses out of a total of 2018 that occurred in our regionof interest around Svalbard (0 to 25° E, 75 to 82° N) inthe considered year of 2008. Matches could only be established during winterand spring, since the low aerosol load during summer in connection with thestrong solar background and the high occurrence rate of clouds stronglyinfluences the performance and reliability of CALIOP observations. Extinctioncoefficients in the range of 2 to 130 Mm at 532 nm were found forsuccessful matches with a difference of a factor of 1.47 (median value for arange from 0.26 to 11.2) between the findings of in situ and spaceborneobservations (the latter being generally larger than the former). Theremaining difference is likely to be due to the natural variability inaerosol concentration and ambient relative humidity, an insufficientrepresentation of aerosol particle growth, or a misclassification of aerosoltype (i.e., choice of lidar ratio) in the CALIPSO retrieval.
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