26 Aug 2020
26 Aug 2020
Characterising optical array particle imaging probes: implications for small ice crystal observations
- 1School of Earth and Environmental Sciences, University of Manchester, UK
- 2National Centre for Atmospheric Science, University of Manchester, UK
- 3Department of Physics and Astronomy, University of Manchester, UK
- 4Particle Chemistry Department, Max Planck Institute for Chemistry, Germany
- 5Institute for Atmospheric Physics, Johannes Gutenberg University, Germany
- 6Met Office, Exeter, UK
- 7Department of Meteorology, University of Reading, UK
- 8Centre for Atmospheric and Climate Processes Research, University of Hertfordshire, UK
- 9British Antarctic Survey, NERC, Cambridge, UK
- anow at: Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
- 1School of Earth and Environmental Sciences, University of Manchester, UK
- 2National Centre for Atmospheric Science, University of Manchester, UK
- 3Department of Physics and Astronomy, University of Manchester, UK
- 4Particle Chemistry Department, Max Planck Institute for Chemistry, Germany
- 5Institute for Atmospheric Physics, Johannes Gutenberg University, Germany
- 6Met Office, Exeter, UK
- 7Department of Meteorology, University of Reading, UK
- 8Centre for Atmospheric and Climate Processes Research, University of Hertfordshire, UK
- 9British Antarctic Survey, NERC, Cambridge, UK
- anow at: Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
Abstract. The cloud particle concentration, size and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory and field experiments. Significant uncertainties are found to exist with such probes for ice crystal measurements. We describe and test two independent methods to constrain a probe's sample volume that removes the most severely mis-sized particles: (1) greyscale image analysis and (2) co-location using stereoscopic imaging. These methods are tested using field measurements from three research flights in cirrus. For these cases, the new methodologies significantly improve agreement with a holographic imaging probe compared to conventional data processing protocols, either removing or significantly reducing the concentration of small ice crystals (< 200 µm) in certain conditions. This work suggests that the observational evidence for a ubiquitous mode of small ice particles in ice clouds is likely due to a systematic instrument bias. Size distribution parameterisations based on OAP measurements need to be revisited using these improved methodologies.
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Sebastian O'Shea et al.


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RC1: 'Review', Anonymous Referee #2, 22 Sep 2020
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AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
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AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
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RC2: 'Reviewer Comment on amt-2020-265', Anonymous Referee #1, 23 Sep 2020
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AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
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AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020


-
RC1: 'Review', Anonymous Referee #2, 22 Sep 2020
-
AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
-
AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
-
RC2: 'Reviewer Comment on amt-2020-265', Anonymous Referee #1, 23 Sep 2020
-
AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
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AC1: 'Authors response', Sebastian O'Shea, 01 Dec 2020
Sebastian O'Shea et al.
Sebastian O'Shea et al.
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