1. 1 Workshop on Measurement Problems in Ice Clouds Topic 7: Properties of cloud particles Co-leaders: Joseph Ulanowski, Simon Alexander Contributors: Alexei Korolev [alexei.korolev@ec.gc.ca] Alfons Schwarzenboeck [A.Schwarzenboeck@opgc.univ-bpclermont.fr] Andrea Flossmann [A.Flossmann@opgc.univ-bpclermont.fr] Ari Leskinen [Ari.Leskinen@fmi.fi] Biagio Esposito [b.esposito@cira.it] Darrel Baumgardner [darrel@dropletmeasurement.com] Dennis Niedermeier [niederm@tropos.de] Greg Michael McFarquhar [mcfarq@illinois.edu] Henner Bieligk [henner@tropos.de] Ismail Gultepe [Ismail.Gultepe@ec.gc.ca] Jessica Meyer [j.meyer@fz-juelich.de] Joseph Z. Ulanowski [z.ulanowski@herts.ac.uk] Martin Gallagher [martin.gallagher@manchester.ac.uk] Martina Kr ä mer [m.kraemer@fz-juelich.de] Mika Komppula [Mika.Komppula@fmi.fi] Olivier Jourdan [O.Jourdan@opgc.univ-bpclermont.fr] Paul Field [paul.field@metoffice.gov.uk] Paul Lawson [plawson@specinc.com] Simon Alexander [Simon.Alexander@aad.gov.au] Ulrich Bundke [bundke@meteor.uni-frankfurt.de] Wolfram Wobrock [W.Wobrock@opgc.univ-bpclermont.fr] Zhien Wang [ZWang@uwyo.edu]

2. 2 1. Theme and Objectives Theme: measured or derived ice particle properties Size (distribution) Shape Sphericity (SID-2, CAS-DEPOL, SID-3, CPSD)  Topics 6 and 11 Surface roughness (SID-3) Fall speed Density Optical properties - extinction coefficient (e.g. CEP - Cloud Extinction Probe) - scattering coefficient - scattering phase function (e.g. Polar Nephelometer, PHIPS) - asymmetry parameter (e.g. CIN - Cloud Integrating Nephelometer) - single scattering albedo - any others?

3. 3 Objectives summarize the strengths and weaknesses of current technology; evaluate the technological progress that has made since June 2010; and identify gaps in our measurement capabilities, where new technology or measurement approaches are needed. Some areas are covered in Topics 1 (Cirrus formation evolution and impact), 6 (Ice/liquid partitioning), 11 (New Sensors)

4. 4 [from Bundke et al. 2010, BAMS 2012 ±verbatim]: - A key question concerns optical properties as a function of ice habit - the single scattering properties of predominant habits must be determined. - Instruments are limited by ice crystal shattering and sample volume uncertainties for sizes 400 μm, given sufficiently long integration times, large uncertainties remain at smaller sizes. - Desirable: in situ measurements of ice particle density. - Ditto simultaneous measurements of complete sets of single scattering properties (phase function, extinction cross section, single scattering albedo). - New tips were designed for probes, and shown to reduce shattering. Software techniques for the removal of closely-spaced particles, assumed to result from shattering, were also proposed (but not yet rigorously evaluated). - New instruments were becoming available to differentiate liquid droplets from ice crystals at sizes <50 μm by detecting their shapes from forward light scattering and depolarization signals; the former could also provide detail of particle shape. Holographic techniques offered the promise of the better definition of sample volume, as well as obtaining images of the detailed structure of ice crystals. [more quotes from Lawson 2010]: - Size distributions of ice particles <10 μm can only be measured with scattering probes, which suffer errors from unknown scattering properties and shattering. SID is the best technological solution, but needs to be quantified. - Size distributions of ice particles 10-50 μm can be measured with the 2D-S and possibly the VIPS. 2D ‑ S DOF and sizing corrections for particles 10-30 μm need more lab calibration. - Size distributions of ice particles >50 μm to a few mm can be measured with the 2D-S, and possibly the CIP and fast 2D-C, but lab evaluations of the CIP and fast 2D-C have not been done. - Habit is best provided by CPI. VIPS and HOLODEC also provide some information. Please add your suggestions, especially regarding remote sensing and modelling 2. Status quo after 2010 workshop

5. 5 3. Recent progress Korolev 2010 [existing anti-shattering algorithms are incapable of effectively filtering out the shattering events from the measurements of the probes such as OAP-2DC and CIP.] Lawson 2011 [while the modified 2D-S tips designed to reduce shattering did reduce the number of shattered particles, the magnitude of the reduction was not as great as when a post- processing routine using particle arrival times was applied] The Korolev 2010 paper and the Lawson 2011 paper agree that both tactics - modified tips and use of post-processing algorithms to remove artifacts - probably comprise the best overall approach.

6. 6 Particle sizing – calibration free? - Rough or complex particles produce “speckle” in SID3 2D scattering patterns - Speckle spots are smaller for larger particles 3. Recent progress

7. 7 - Size is inversely proportional to median spot area. - Size depends on n etc. only weakly - if particles are rough or complex (Ulanowski et al. 2012a). 3. Recent progress

8. 8 CPSD probe [Darrel to contribute? Or in Topic 11?]

9. 9 3. Recent progress Lindqvist et al. 2013 - Ice-cloud particle habit classification using principal components [Greg to contribute?]

10. 10 3. Recent progress Ice particle roughness (mostly remote sensing) Gayet et al. (2011) - particles with imperfect or complex shapes are prevalent Baum et al (2011) - space-borne lidar depolarization measurements could only be explained by modeling ice crystals with rough surfaces. Cole et al (2013) - very rough-faceted particles provide an improved fit to the polarized reflectance from PARASOL.

11. 11 3. Recent progress Ice particle roughness (cont.) In situ SID-3 data indicates strong roughness in the majority of ice in mid-latitude cloud cases (Ulanowski 2010, 2012). Smooth ice analogue Rough ice analogue SID3 scattering patterns give a measure of roughness Ice analogue corresponding to typical roughness in cirrus

12. 12 3. Recent progress Ice particle roughness (cont.) Ice roughness as measured by SID3 is proportional to supersaturation (M. Schnaiter)

13. 13 3. Recent progress Ice particle roughness (cont.) G. Ritter … Growth/sublimation cycles can produce increasing roughness (C. Chou, Voigtl ä nder et al. 2013) … (A) SEM view of a growing ice crystal. (B) The same crystal after ~15 min of evaporation (Pfalzgraf 2010). ICCP-2012 – sublimation …

14. 14 3. Recent progress Modelling DESCAM CRM (Flossmann & Wobrock 2010): - Multiple growth/sublimation cycles can be present - Supersaturation is linked to aerosol concentration

15. 15 3. Recent progress Single scattering property modelling (Yang et al. 2013): Database of spectrally consistent scattering, absorption, and polarization properties of ice crystals at wavelengths from 0.2 to 100 µ m. For each ice crystal habit, three surface roughness conditions (i.e., smooth, moderately roughened, and severely roughened) are considered to account for the surface texture of large particles.

16. 16 3. Recent progress Simultaneous high-res stereo imaging and phase function measurement – PHIPS (Sch ö n et al. 2011, Abdelmonem et al. 2011)

17. 17 3. Recent progress Cotton et al. (2012) The effective density of small ice particles obtained from in situ aircraft observations of mid-latitude cirrus. [Paul Field to contribute?] Polar Nephelometer update [Olivier Jourdan to contribute?] Cloud Extinction Probe update [Alexei Korolev to contribute?]

18. 18 3. Recent progress Please send in your contribution for in situ measurement or modelling. Note that Simon Alexander is coordinating the remote sensing contributions.

19. 19 4. Measurement gaps Problems In situ: - shattering still an issue - small particle contribution to PSD - roughness/complexity: determine both actual roughness and impact on optical properties e.g. g (through single-scattering models or simultaneous measurement) - measurements at low scattering angle needed for phase function or g Modelling: - "Modelling of the ice phase in clouds is trapped between Not enough information and Too much information" (Wobrock & Flossman) Please add your suggestions

20. 20 4. Measurement gaps Solutions? - Combine open path or anti-shatter tips with interarrival time? Measure roughness through speckle patterns (SID-3), high-res holography? - Combine morphology with optical properties, e.g. phase function (e.g. PHIPS)? Please add your suggestions

21. 21 References Abdelmonem, A.; Schnaiter, M.; Amsler, P.; Hesse, E.; Meyer, J.; Leisner, T. (2011) First correlated measurements of the shape and scattering properties of cloud particles using the new Particle Habit Imaging and Polar Scattering (PHIPS) probe. Atmos. Meas. Tech., 4, 2125-2142. Baum, B. A., P. Yang, A. J. Heymsfield, C. G. Schmitt, Y. Xie, A. Bansemer, Y-X, Hu, Z. Zhang (2011) Improvements in shortwave bulk scattering and absorption models for the remote sensing of ice clouds., J. Appl. Meterol. Climatol., 50, 1037-1056. Baumgardner D. et al. 2012 In situ, airborne instrumentation: addressing and solving measurement problems in ice clouds. Bull. Amer. Meteor. Soc., 93, ES29-ES34. Bundke U., Gayet, Mőhler O., Wendisch M., Stetzer O., Petters M.D. 2010 Properties of cloud particles. Workshop on airborne, in situ instrumentation to measure ice clouds. Seaside, Oregon, USA. Cole, B. H., Yang, P., Baum, B. A., Riedi, J., Labonnote, L. C., Thieuleux, F., & Platnick, S. (2013). Comparison of PARASOL observations with polarized reflectances simulated using different ice habit mixtures. J. Appl. Meteor. Climatol. 52, 186-196. Cotton, R. J., Field, P. R., Ulanowski, Z., Kaye, P. H., Hirst, E., Greenaway, R. S., Crawford, I., Crosier, J. and Dorsey, J. (2012) The effective density of small ice particles obtained from in situ aircraft observations of mid-latitude cirrus. Q. J. Royal Met. Soc. DOI: 10.1002/qj.2058 Flossmann, A. I., Wobrock, W. (2010) A review of our understanding of the aerosol-cloud interaction from the perspective of a bin resolved cloud scale modeling. Atmos. Res. 97, 478-497. Gayet, J.-F., Mioche, G., Shcherbakov, V., Gourbeyre, C., Busen, R., and Minikin, A. (2011) Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment, Atmos. Chem. Phys. 11, 2537-2544. Korolev A. V., E. F. Emery, J. W. Strapp, S. G. Cober, G. A. Isaac, M. Wasey, D. Marcotte (2011) Small ice particles in tropospheric clouds: fact or artifact? Airborne Icing Instrumentation Evaluation Experiment. Bull. Am. Met. Soc. 92, 967-973. Lawson R. P. 2010 Instrument limitations and uncertainties. Workshop on airborne, in situ instrumentation to measure ice clouds. Seaside, Oregon. Lawson, R. P. 2011 Effects of ice particles shattering on the 2D-S probe. Atmos. Meas. Tech. 4, 1361-1381. Lindqvist, H., K. Muinonen, T. Nousiainen, J. Um, G. M. McFarquhar, P. Haapanala, R. Makkonen, H. Hakkarainen. (2012) Ice-cloud particle habit classification using principal components. J. Geophys. Res. 117, D16206. Pfalzgraff W. C., R. M. Hulscher, and S. P. Neshyba (2010) Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals. Atmos. Chem. Phys. 10, 2927–2935. R. Schön, M. Schnaiter, Z. Ulanowski, S. Benz, O. Möhler, S. Vogt, R. Wagner & U. Schurath (2011) Particle habit imaging using incoherent light: a first step towards a novel instrument for cloud microphysics. J. Atm. Oceanic Technol. 28, 493-512. Ulanowski, Z., P.H. Kaye, E. Hirst & R.S. Greenaway (2010) Light scattering by ice particles in the Earth's atmosphere and related laboratory measurements. In: Proc. 12th Int. Conf. Electromagnetic & Light Scatt., Helsinki, pp. 294-297. http://www.helsinki.fi/els/articles/74/article.pdf Ulanowski Z., P. H. Kaye, E. Hirst, R. S. Greenaway, R. Cotton (2012) Rough and irregular ice crystals in mid-latitude clouds, 16th Int. Conf. Clouds Precipitation, Leipzig. http://researchprofiles.herts.ac.uk/portal/files/1838820/Ulanowski_ICCP_2012_extended.pdf Ulanowski Z., E. Hirst, P.H. Kaye, R. Greenaway (2012a) Retrieving the size of particles with rough and complex surfaces from two-dimensional scattering patterns. J. Quantit. Spectr. Rad. Transf. 113, 2457-2464 Ulanowski Z., P.H. Kaye, E. Hirst, R.S. Greenaway, E. Hesse1, R.J. Cotton (in preparation) Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements. ACPD. Voigtländer, J. H. Bieligk, D. Niedermeier, T. Clauss, C. Chou, Z. Ulanowski, F. Stratmann 2013 A new experimental setup to investigate nucleation, dynamic growth and surface properties of single ice crystals. EGU, Vienna. Yang, P., Bi, L., Baum, B. A., Liou, K. N., Kattawar, G. W., Mishchenko, M. I., & Cole, B. (2013). Spectrally consistent scattering, absorption, and polarization properties of atmospheric ice crystals at wavelengths from 0.2 to 100 µ m. J. Atm. Sci. 70, 330-347.