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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 3 | Copyright
Atmos. Meas. Tech., 11, 1639-1651, 2018
https://doi.org/10.5194/amt-11-1639-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Mar 2018

Research article | 26 Mar 2018

Impact of varying lidar measurement and data processing techniques in evaluating cirrus cloud and aerosol direct radiative effects

Simone Lolli1,2, Fabio Madonna1, Marco Rosoldi1, James R. Campbell3, Ellsworth J. Welton4, Jasper R. Lewis2, Yu Gu5, and Gelsomina Pappalardo1 Simone Lolli et al.
  • 1CNR-IMAA, Istituto di Metodologie Ambientali, Tito Scalo (PZ), Italy
  • 2NASA GSFC-JCET, Code 612, Greenbelt, MD, USA
  • 3Naval Research Laboratory, Monterey, CA, USA
  • 4NASA GSFC, Code 612, Greenbelt, MD, USA
  • 5University of California Los Angeles (UCLA), Los Angeles, CA, USA

Abstract. In the past 2 decades, ground-based lidar networks have drastically increased in scope and relevance, thanks primarily to the advent of lidar observations from space and their need for validation. Lidar observations of aerosol and cloud geometrical, optical and microphysical atmospheric properties are subsequently used to evaluate their direct radiative effects on climate. However, the retrievals are strongly dependent on the lidar instrument measurement technique and subsequent data processing methodologies. In this paper, we evaluate the discrepancies between the use of Raman and elastic lidar measurement techniques and corresponding data processing methods for two aerosol layers in the free troposphere and for two cirrus clouds with different optical depths. Results show that the different lidar techniques are responsible for discrepancies in the model-derived direct radiative effects for biomass burning (0.05Wm−2 at surface and 0.007Wm−2 at top of the atmosphere) and dust aerosol layers (0.7Wm−2 at surface and 0.85Wm−2 at top of the atmosphere).

Data processing is further responsible for discrepancies in both thin (0.55Wm−2 at surface and 2.7Wm−2 at top of the atmosphere) and opaque (7.7Wm−2 at surface and 11.8Wm−2 at top of the atmosphere) cirrus clouds. Direct radiative effect discrepancies can be attributed to the larger variability of the lidar ratio for aerosols (20–150sr) than for clouds (20–35sr). For this reason, the influence of the applied lidar technique plays a more fundamental role in aerosol monitoring because the lidar ratio must be retrieved with relatively high accuracy. In contrast, for cirrus clouds, with the lidar ratio being much less variable, the data processing is critical because smoothing it modifies the aerosol and cloud vertically resolved extinction profile that is used as input to compute direct radiative effect calculations.

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We evaluate the comparability of aerosol and cloud vertically resolved optical properties obtained with varying lidar profiling techniques and/or data processing methodologies. The discrepancies are assessed by evaluating climate-sensitive direct radiative effects, computed by radiative transfer code means. Results show important discrepancies up to 0.8 W m−2 due to lidar data smoothing in cirrus clouds and a 0.05 W m−2 difference between Raman and elastic lidar technique on a dust layer aloft.
We evaluate the comparability of aerosol and cloud vertically resolved optical properties...
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