Preprints
https://doi.org/10.5194/acp-2022-154
https://doi.org/10.5194/acp-2022-154
 
16 Mar 2022
16 Mar 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Evaluation of aerosol number concentrations from CALIPSO with ATom airborne in-situ measurements

Goutam Choudhury1, Albert Ansmann2, and Matthias Tesche1 Goutam Choudhury et al.
  • 1Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
  • 2Leibniz Institute for Tropospheric Research, Leipzig, Germany

Abstract. The present study aims to evaluate the available aerosol number concentration (ANC) retrieval algorithms for spaceborne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) aboard CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite with the airborne in-situ measurements from ATom (Atmospheric Tomography Mission) campaign. We used HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory model) to match both the measurements in space and identified 53 cases that were suitable for comparison. Since the ATom data include dry aerosol extinction coefficient, we used kappa parameterization to adjust the ambient measurements from CALIOP to dry conditions. As both the datasets have a different vertical resolution, we re-grid them to uniform height bins of 240 m from the surface to a height of 5 km. On comparing the dry extinction coefficients, we found a reasonable agreement between the CALIOP and ATom measurements with Spearman’s correlation coefficient of 0.715. Disagreement was found mostly for retrievals above 3 km altitude. Thus, to compare the ANC which may vary orders of magnitude in space and time, we further limit the datasets and only select those height bins for which the CALIOP derived dry extinction coefficient is within ±50 % of the ATom measurements. This additional filter further increases the probability of comparing the same air parcel. The altitude bins which qualify the extinction coefficient constraint are used to estimate ANC with dry radius >50 nm (n50,dry) and >250 nm (n250,dry). The POLIPHON (Polarization Lidar Photometer Networking) and OMCAM (Optical Modelling of CALIPSO Aerosol Microphysics) algorithms were used to estimate the n50,dry and n250,dry. The POLIPHON estimates of n50,dry and n250,dry were found to be in good agreement with the in-situ measurements with a correlation coefficient of 0.829 and 0.47, respectively. The OMCAM estimates of n50,dry and n250,dry were also in reasonable agreement with the in-situ measurements with a correlation coefficient of 0.823 and 0.463, respectively. However, we found that the OMCAM estimated n50,dry were about an order less than the in-situ measurements for marine dominated cases. We propose a modification to the OMCAM algorithm by using an AERONET-based marine model. With the updated OMCAM algorithm, the n50,dry agree well with the ATom measurements. Such concurrence between the satellite-derived ANC and the independent ATom in-situ measurements emboldens the use of CALIOP in studying the aerosol-cloud interactions.

Goutam Choudhury et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-154', Charles Brock, 30 Mar 2022
  • RC2: 'Comment on acp-2022-154', Anonymous Referee #2, 16 Apr 2022
  • AC1: 'Comment on acp-2022-154', Goutam Choudhury, 06 May 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-154', Charles Brock, 30 Mar 2022
  • RC2: 'Comment on acp-2022-154', Anonymous Referee #2, 16 Apr 2022
  • AC1: 'Comment on acp-2022-154', Goutam Choudhury, 06 May 2022

Goutam Choudhury et al.

Goutam Choudhury et al.

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Short summary
Lidars provide height-resolved type-specific aerosol properties and are key in studying vertically collocated aerosols and clouds. In this study, we compare the aerosol number concentrations derived from spaceborne lidar with the in-situ flight measurements. Our results show a reasonable agreement between both datasets. Such an agreement has not been achieved yet. It shows the potential of spaceborne lidar in studying aerosol-cloud interactions much needed to improve our model forecasts.
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