Abstract
Abstract. In this study we investigate to what degree it is possible to reconcile continuously recorded particle light extinction coefficients derived from dry in situ measurements at Zeppelin station (78.92° N, 11.85° E; 475 m above sea level), Ny-Ålesund, Svalbard, that are recalculated to ambient relative humidity, as well as simultaneous ambient observations with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. To our knowledge, this represents the first study that compares spaceborne lidar measurements to optical aerosol properties from short-term in situ observations (averaged over 5 h) on a case-by-case basis. Finding suitable comparison cases requires an elaborate screening and matching of the CALIOP data with respect to the location of Zeppelin station as well as the selection of temporal and spatial averaging intervals for both the ground-based and spaceborne observations. Reliable reconciliation of these data cannot be achieved with the closest-approach method, which is often used in matching CALIOP observations to those taken at ground sites. This is due to the transport pathways of the air parcels that were sampled. The use of trajectories allowed us to establish a connection between spaceborne and ground-based observations for 57 individual overpasses out of a total of 2018 that occurred in our region of interest around Svalbard (0 to 25° E, 75 to 82° N) in the considered year of 2008. Matches could only be established during winter and spring, since the low aerosol load during summer in connection with the strong solar background and the high occurrence rate of clouds strongly influences the performance and reliability of CALIOP observations. Extinction coefficients in the range of 2 to 130 Mm−1 at 532 nm were found for successful matches with a difference of a factor of 1.47 (median value for a range from 0.26 to 11.2) between the findings of in situ and spaceborne observations (the latter being generally larger than the former). The remaining difference is likely to be due to the natural variability in aerosol concentration and ambient relative humidity, an insufficient representation of aerosol particle growth, or a misclassification of aerosol type (i.e., choice of lidar ratio) in the CALIPSO retrieval.
Highlights
Introduction and motivationUnderstanding and quantifying the climatic effects of natural and anthropogenic aerosols from direct observations requires a combination of data from a variety of instruments that usually apply very different measurement techniques
About 10 % of all Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) profiles contain neither aerosol nor cloud features with a maximum and minimum occurrence rate of 25 and 4 % in July and January, respectively. This effect is due to the weaker signalto-noise ratio (SNR) of CALIOP measurements during bright daytime conditions compared to the absence of sunlight during night and the correspondingly higher threshold value that has to be exceeded for feature detection (Winker et al, 2009; Young and Vaughan, 2009)
To coarsely account for uncertainties in the trajectories, in situ extinction coefficients were averaged over 5 h centered around the time when the in situ instruments sampled the same air parcels as CALIOP, i.e., time of a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) overpass plus the time lag determined from the length of the trajectories that connect this overpass to Zeppelin station
Summary
Understanding and quantifying the climatic effects of natural and anthropogenic aerosols from direct observations requires a combination of data from a variety of instruments that usually apply very different measurement techniques. In principle, such an analysis connects information on the vertical and horizontal aerosol distribution from the CALIPSO satellite data to the more specific information about aerosol microphysical and chemical properties at the surface. Note that it is more likely that the aerosol-containing planetary boundary layer at Svalbard is between 0.5 and 1.0 km deep – which would decrease the maximum AOT as derived from the values presented in Di Pierro et al (2013) even further This discrepancy calls for a more detailed investigation of the factors that influence the reconciliation of extinction coefficients from ground-based and spaceborne observations.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
