ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-727-2012 On the observation of unusual high concentration of small chain-like aggregate ice crystals and large ice water contents near the top of a deep convective cloud during the CIRCLE-2 experiment Gayet J.-F. 1 Mioche G. 1 Bugliaro L. 2 Protat A. 3 Minikin A. 2 Wirth M. 2 Dörnbrack A. 2 Shcherbakov V. 1 4 Mayer B. 2 Garnier A. 3 Gourbeyre C. 1 Laboratoire de Météorologie Physique, UMR6016 CNRS/Université Blaise Pascal, Clermont-Ferrand, France Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany Laboratoire Atmosphères, Milieux, Observations Spatiales, UMR8190 CNRS/Université Pierre et Marie Curie, France Laboratoire de météorologie Physique, Institut Universitaire de Technologie de Montluçon, Montluçon, France 16 01 2012 12 2 727 744 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/727/2012/acp-12-727-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/727/2012/acp-12-727-2012.pdf

During the CIRCLE-2 experiment carried out over Western Europe in May 2007, combined in situ and remote sensing observations allowed to describe microphysical and optical properties near-top of an overshooting convective cloud (11 080 m/−58 °C). The airborne measurements were performed with the DLR Falcon aircraft specially equipped with a unique set of instruments for the extensive in situ cloud measurements of microphysical and optical properties (Polar Nephelometer, FSSP-300, Cloud Particle Imager and PMS 2-D-C) and nadir looking remote sensing observations (DLR WALES Lidar). Quasi-simultaneous space observations from MSG/SEVIRI, CALIPSO/CALIOP-WFC-IIR and CloudSat/CPR combined with airborne RASTA radar reflectivity from the French Falcon aircraft flying above the DLR Falcon depict very well convective cells which overshoot by up to 600 m the tropopause level. Unusual high values of the concentration of small ice particles, extinction, ice water content (up to 70 cm<sup>−3</sup>, 30 km<sup>−1</sup> and 0.5 g m<sup>−3</sup>, respectively) are experienced. The mean effective diameter and the maximum particle size are 43 μm and about 300 μm, respectively. This very dense cloud causes a strong attenuation of the WALES and CALIOP lidar returns. The SEVIRI retrieved parameters confirm the occurrence of small ice crystals at the top of the convective cell. Smooth and featureless phase functions with asymmetry factors of 0.776 indicate fairly uniform optical properties. Due to small ice crystals the power-law relationship between ice water content (IWC) and radar reflectivity appears to be very different from those usually found in cirrus and anvil clouds. For a given equivalent reflectivity factor, IWCs are significantly larger for the overshooting cell than for the cirrus. Assuming the same prevalent microphysical properties over the depth of the overshooting cell, RASTA reflectivity profiles scaled into ice water content show that retrieved IWC up to 1 g m<sup>−3</sup> may be observed near the cloud top. Extrapolating the relationship for stronger convective clouds with similar ice particles, IWC up to 5 g m<sup>−3</sup> could be experienced with reflectivity factors no larger than about 20 dBZ. This means that for similar situations, indication of rather weak radar echo does not necessarily warn the occurrence of high ice water content carried by small ice crystals. All along the cloud penetration the shape of the ice crystals is dominated by chain-like aggregates of frozen droplets. Our results confirm previous observations that the chains of ice crystals are found in a continental deep convective systems which are known generally to generate intense electric fields causing efficient ice particle aggregation processes. Vigorous updrafts could lift supercooled droplets which are frozen extremely rapidly by homogeneous nucleation near the −37 °C level, producing therefore high concentrations of very small ice particles at upper altitudes. They are sufficient to deplete the water vapour and suppress further nucleation as confirmed by humidity measurements. These observations address scientific issues related to the microphysical properties and structure of deep convective clouds and confirm that particles smaller than 50 μm may control the radiative properties in convective-related clouds. These unusual observations may also provide some possible insights regarding engineering issues related to the failure of jet engines commonly used on commercial aircraft during flights through areas of high ice water content. However, large uncertainties of the measured and derived parameters limit our observations.

 References Abraham, J., Strapp, J. W., Fogarty, C., and Wolde, M.: Extratropical transition of Hurricane Michael, Bull. Amer. Met. Soc., 85, 1323–1339, 2004. Bögel, W. and Baumann, R.: Test and calibration of the DLR Falcon wind measuring system by maneuvers, J. Atmos. Oceanic Technol., 8, 5–18, 1991. Boudala, F. S., Isaac, G. A., and Hudak, D.: Ice water content and precipitation rate as a function of equivalent radar reflectivity and temperature based on in situ observations, J. Geophys. Res., 111, D11202, http://dx.doi.org/10.1029/2005JD006499doi:10.1029/2005JD006499, 2006. Bouniol, D., Protat, A., Plana-Fattori, A., Giraud, M., Vinson, J.-P., and Grand, N.: Comparison of airborne and spaceborne 95-GHz radar reflectivity and evidence of multiple scattering effects in spaceborne measurements, J. Atmos. Oceanic Technol., 25, 1983–1995, 2008. Borrmann, S., Luo, B., and Mishchenko, M.: Application of the T-matrix method to the measurement of aspherical (ellipsoidal) particles with forward scattering optical particle counters, J. Aerosol Sci., 31, 789–799, 2000. Bringi, V., Seliga, T., and Cooper, W.: Analysis of aircraft hydrometeor spectra and differential reflectivity (ZDR) radar measurements during the Cooperative Convective Precipitation Experiment, Radio Sci., 19, 157–167, 1984. Bugliaro, L., Zinner, T., Keil, C., Mayer, B., Hollmann, R., Reuter, M., and Thomas, W.: Validation of cloud property retrievals with simulated satellite radiances: a case study for SEVIRI, Atmos. Chem. Phys., 11, 5603–5624, http://dx.doi.org/10.5194/acp-11-5603-2011doi:10.5194/acp-11-5603-2011, 2011. Busen, R. and Buck, A. L.: A high-performance hygrometer for aircraft use: Description, installation, and flight data, J. Atmos. Oceanic Technol., 12, 73–84, doi:10.1175/1520-0426(1995)012<0073:AHPHFA>2.0.CO;2doi:10.1175/1520-0426(1995)012<0073:AHPHFA>2.0.CO;2, 1995. Connolly, P. J., Saunders, C. P. R., Gallagher, M. W., Bower, K. N., Flynn, M. J., Choularton, T. W., Whiteway, J., and Lawson, R. P.: Aircraft observations of the influence of electric fields on the aggregation of ice crystals, Q. J. R. Meteorol. Soc., 131, 1695–1712, 2005. Connolly, P. J., Flynn, M. J., Ulanowski, Z., Choularton, T. W., Gallagher, M. W., and Bower, K. N.: Calibration of the cloud particle imager probes using calibration beads and ice crystal analogues: The depth of field, J. Atmos. Oceanic Technol., 24, 1860–1879, 2007. Eichler, H., Ehrlich, E., Wendisch, M., Mioche, G., Gayet, J.-F., Wirth, M., Emde, C., and Minikin, A.: Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study, J. Geophys. Res., 114, D19203, http://dx.doi.org/10.1029/2009JD012215doi:10.1029/2009JD012215, 2009. Davis, S. M., Avallone, L. M., Kahn, B. H., Meyer, K. G., and Baumgärdner, D.: Comparison of airborne in situ measurements and Moderate Resolution Imaging Spectroradiometer(MODIS) retrievals of cirrus cloud optical and microphysical properties during the Midlatitude Cirrus Experiment (MidCiX), J. Geophys. Res., 114, D02203, http://dx.doi.org/10.1029/2008JD010284doi:10.1029/2008JD010284, 2009. Field, P. R., Heymsfield A. J., and Bansemer, A.: Shattering and interarrival times measured by optical array probes in ice clouds, J. Atmos. Oceanic Technol., 23, 1357–1371, http://dx.doi.org/10.1175/JTECH1922.1doi:10.1175/JTECH1922.1, 2006. Fridlind, A. M., Ackerman, A. S., Jensen, E. J., Heymsfield, A. J., Poellot, M. R., Stevens, D. E., Wang, D., Miloshevich, L. M., Baumgärdner, D., Lawson, R. P., Wilson, J. C., Flagan, R. C., Seinfeld, J. H., Jonsson, H. H., VanReken, T. M., Varutbangkul, V., and Rissman, T. A.: Evidence for the predominance of mid-tropospheric aerosols as subtropical anvil nuclei, Science, 304, 718–722, http://dx.doi.org/10.1126/science.1094947doi:10.1126/science.1094947, 2004. %Frey, W., Borrmann, S., Kunkel, D., Weigel, R., de Reus, M., Schlager, H., %Roiger, A., Voigt, C., Hoor, P., Curtius, J., Krämer, M., Schiller, C., %Volk, C. M., Homan, C. D., Fierli, F., Di Donfrancesco, G., Ulanovsky, A., %Ravegnani, F., Sitnikov, N. M., Viciani, S., D'Amato, F., Shur, G. N., %Belyaev, G. V., Law, K. S., and Cairo, F.: In-situ measurements of tropical %cloud properties in the West African monsoon: upper tropospheric ice clouds, %mesoscale convective system outflow, and subvisual cirrus, Atmos. Chem. %Phys. Discuss., 11, 745–812, http://dx.doi.org/10.5194/acpd-11-745-2011doi:10.5194/acpd-11-745-2011, 2011. Frey, W., Borrmann, S., Kunkel, D., Weigel, R., de Reus, M., Schlager, H., Roiger, A., Voigt, C., Hoor, P., Curtius, J., Krämer, M., Schiller, C., Volk, C. M., Homan, C. D., Fierli, F., Di Donfrancesco, G., Ulanovsky, A., Ravegnani, F., Sitnikov, N. M., Viciani, S., D'Amato, F., Shur, G. N., Belyaev, G. V., Law, K. S., and Cairo, F.: In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus, Atmos. Chem. Phys., 11, 5569–5590, http://dx.doi.org/10.5194/acp-11-5569-2011doi:10.5194/acp-11-5569-2011, 2011. Gallagher, M. W., Connolly, P. J., Whiteway, J., Figuera-Nieto, D., Flynn, M., Choularton, T. W., Bower, K. N., Cook, C., Busen, R., and Hacker, J.: An overview of the microphysical structure of cirrus clouds observed during EMERALD-1, Q. J. Meteorol. Soc., 131, 1143–1169, http://dx.doi.org/10.1256/qj.03.138doi:10.1256/qj.03.138, 2005. Garrett, T. J., Gerber, H., Baumgärdner, D. G., Twohy, C. H., and Weinstock, E. M.: Small, highly reflective ice crystals in low-latitude cirrus, Geophys. Res. Lett., 30, 2132, http://dx.doi.org/10.1029/2003GL018153doi:10.1029/2003GL018153, 2003. %Gayet, J. F., Crépel, O., Fournol, J. F., and Oshchepkov, S.: A new %airborne polar Nephelometer for the measurements of optical and %microphysical cloud properties. Part I: Theoretical design, Ann. Geophys., %15, 451–459, http://dx.doi.org/10.1007/s00585-997-0451-1doi:10.1007/s00585-997-0451-1, 1997. Gayet, J. F., Crépel, O., Fournol, J. F., and Oshchepkov, S.: A new airborne polar Nephelometer for the measurements of optical and microphysical cloud properties. Part I: Theoretical design, Ann. Geophys., 15, 451–459, http://dx.doi.org/10.1007/s00585-997-0451-1doi:10.1007/s00585-997-0451-1, 1997. Gayet, J.-F., Auriol, F., Minikin, A., Ström, J., Seifert, M., R. Krejci, R., Petzold, A., Febvre, G., and Schumann, U.: Quantitative measurement of the microphysical and optical properties of cirrus clouds with four different in situ probes: Evidence of small ice crystals, Geophys. Res. Lett., 29, 2230, http://dx.doi.org/10.1029/2001GL014342doi:10.1029/2001GL014342, 2002. Gayet, J.-F., Ovarlez, J., Shcherbakov, V., Ström, J., Schumann, U., Minikin, A., Auriol, F., Petzold, A., and Monier, M.: Cirrus cloud microphysical and optical properties at southern and northern midlatitudes during the INCA experiment, J. Geophys. Res., 109, D20206, http://dx.doi.org/10.1029/2004JD004803doi:10.1029/2004JD004803, 2004. %Gayet, J.-F., Mioche, G., Dörnbrack, A., Ehrlich, A., Lampert, A., and %Wendisch, M.: Microphysical and optical properties of Arctic mixed-phase %clouds. The 9 April 2007 case study, Atmos. Chem. Phys., 9, 6581–6595, %http://dx.doi.org/10.5194/acp-9-6581-2009doi:10.5194/acp-9-6581-2009, 2009. Gayet, J.-F., Mioche, G., Dörnbrack, A., Ehrlich, A., Lampert, A., and Wendisch, M.: Microphysical and optical properties of Arctic mixed-phase clouds. The 9 April 2007 case study., Atmos. Chem. Phys., 9, 6581–6595, http://dx.doi.org/10.5194/acp-9-6581-2009doi:10.5194/acp-9-6581-2009, 2009. Gayet, J.-F., Mioche, G., Shcherbakov, V., Gourbeyre, C., Busen, R., and Minikin, A.: Optical properties of pristine ice crystals in mid-latitude cirrus clouds: a case study during CIRCLE-2 experiment, Atmos. Chem. Phys., 11, 2537–2544, http://dx.doi.org/10.5194/acp-11-2537-2011doi:10.5194/acp-11-2537-2011, 2011. Heymsfield, A. J.: Ice particle evolution in the anvil of a severe thunderstorm during CCOPE, J. Atmos. Sci., 43, 2463–2478, 1986. Heymsfield, A. J.: On measurements of small ice particles in clouds, Geophys. Res. Lett., 34, L23812, http://dx.doi.org/10.1029/2007GL030951doi:10.1029/2007GL030951, 2007. Heymsfield, A. J. and Palmer, A.: Relationship for deriving thunderstorm anvil ice mass for CCOPE storm weather estimates, J. Clim. Appl. Meteorol., 25, 691–702, 1986. Heymsfield, A. J., Miloshevich, L. M., Schmitt, C., Bansemer, A., Twohy, C., Poellot, M. R., Fridlind, A., and Gerber, H.: Homogeneous ice nucleation in subtropical and tropical convection and its influence on cirrus anvil microphysics, J. Atmos. Sci., 62, 41–64, 2005. Heymsfield, A. J., Bansemer, A., Durden, S. L., Herman, R. L., and Bui, T. P.: Ice microphysics observations in Hurricane Humberto: Comparison with non-hurricane-generated ice cloud layers, J. Atmos. Sci., 63, 288–308, 2006. Heymsfield, A. J., Bansemer, A., Heymsfield, G., and Fierro, A. O.: Microphysics of Maritime Tropical Convective Updrafts at Temperatures from −20 to −60 °C, J. Atmos. Sci., 66, 3530–3562, 2009. Hunt, W. H, Winker, D. M., Vaughan, M. A., Powell, K. A., Lucker, P. L., and Weimer, C.: CALIPSO Lidar Description and Performance Assessment, J. Atmos. Ocean Technol., 26, 1214–1228, http://dx.doi.org/10.1175/2009JTECHA1223.1doi:10.1175/2009JTECHA1223.1, 2009. Isaac, G. A., Korolev, A. V., Strapp, J. W., Cober, S. G., Boudala, F. S., Marcotte, D., and Reich, V. L.: Assessing the collection efficiency of natural cloud particles impacting the Nevzorov total water content probe. AIAA 44th Aerospace Sciences Meeting and Exhibit, Reno, Nevada, 9–12 January 2006, AIAA-2006-1221, 2006. Jensen, E. J., Lawson, P., Baker, B., Pilson, B., Mo, Q., Heymsfield, A. J., Bansemer, A., Bui, T. P., McGill, M., Hlavka, D., Heymsfield, G., Platnick, S., Arnold, G. T., and Tanelli, S.: On the importance of small ice crystals in tropical anvil cirrus, Atmos. Chem. Phys., 9, 5519–5537, http://dx.doi.org/10.5194/acp-9-5519-2009doi:10.5194/acp-9-5519-2009, 2009. Jourdan, O., Mioche, G., Garret, T. J., Schwarzenbock, A., Vidot, J., Xie, Y., Shcherbakov, V., Duroure, C., Yang, P., and Gayet, J.-F.: Coupling of the microphysical and optical properties of arctic clouds during the ASTAR 2004 experiment: Implications for light scattering modelling, J. Geophys. Res., 115, D23206, http://dx.doi.org/10.1029/2010JD014016doi:10.1029/2010JD014016, 2010. Knollenberg, R. G., Kelly, K., and Wilson, J. C.: Measurements of high number densities of ice crystals in the tops of tropical cumulonimbus, J. Geophys. Res., 98, 8639–8664, http://dx.doi.org/10.1029/92JD02525doi:10.1029/92JD02525, 1993. Korolev, A. V. and Isaac, G. A.: Shattering during sampling by OAPs and HVPS, Part I: Snow particles, J. Atmos. Ocean Technol., 22, 528–543, 2005. Korolev, A. V., Strapp, J. W., Isaac, G. A., and Emery, E.: Improved airborne hot-wire measurements of ice water content in clouds, Proceedings 15th Intl. Conf. on Clouds and Precipitation, Cancun, Mexico, Extended Abstracts Paper P13.4, (available online: http://cabernet.atmosfcu.unam.mx/ICCP-2008/), 2008. Korolev, A. V., Emery, E. F., Strapp, J. W., Cober, S. G., Isaac, G. A., Wasey, M., and Marcotte, D.: Small Ice Particles in Tropospheric Clouds: Fact or Artifact? Airborne Icing Instrumentation Evaluation Experiment, Bull. Am. Meteorol. Soc., 92, 967–973, http://dx.doi.org/10.1175/2010BAMS3141.1doi:10.1175/2010BAMS3141.1, 2011. Lawson, R. P.: Effects of ice particles shattering on the 2-D-S probe, Atmos. Meas. Tech., 4, 1361–1381, http://dx.doi.org/10.5194/amt-4-1361-2011doi:10.5194/amt-4-1361-2011, 2011. Lawson, R. P., Angus, L. G., and Heymsfield, A. J.: Cloud particle measurements in thunder storm anvils and possible weather threat to aviation, J. Aircraft, 35, 113–121, 1998. Lawson, R. P., Baker, B. A., Schmitt, C. G., and Jensen, T. L.: In situ measurements of microphysical properties of mid-latitude and anvil cirrus and validation of satellite retrievals'. Paper no. TS 32.4, Proceedings of 30th International conference on remote sensing of environment, Honolulu, Hawaii, http://www.symposia.org/proceedings.htm, 2003. Lawson, R. P., O'Connor, D., Zmarzly, P., Weaver, K., Baker, B. A., Mo, Q., and Jonsson, H.: The 2-D-S (Stereo) probe: Design and preliminary tests of a new airborne, high-speed, high-resolution imaging probe, J. Atmos. Oceanic Technol., 23, 1462–1477, http://dx.doi.org/10.1175/JTECH1927.1doi:10.1175/JTECH1927.1, 2006a. Lawson, R. P., Baker, B., Pilson, B., and Mo, Q.: In Situ Observations of the Microphysical Properties of Wave, Cirrus, and Anvil Clouds, Part II: Cirrus Clouds, J. Atmos. Sci., 63, 3186–3203, 2006b. Lawson, R. P., Jensen, E., Mitchell, D. L., Baker, B., Mo, Q., and Pilson, B.: Microphysical and radiative properties of tropical clouds investigated in TC4 and NAMMA, J. Geophys. Res., 115, D00J08, http://dx.doi.org/10.1029/2009JD013017doi:10.1029/2009JD013017, 2010. Mason, J. G., Strapp, J. W., and Chow, P.: The ice particle threat to engines in flight. 44th AIAA Aerospace Sciences Meeting, Reno, Nevada, 9–12 January 2006, AIAA-2006-206, 2006. Mazzawy, R. S. and Strapp, J. W.: Appendix D – An Interim Icing Envelope: High Ice Crystal Concentrations and Glaciated Conditions, 2007 SAE Aircraft and Engine Icing International Conference, doi:10.4271/2007-01-3311, 2007. McFarquhar, G. M. and Heymsfield, A. J.: Microphysical characteristics of three anvils sampled during the Central Equatorial Pacific Experiment, J. Atmos. Sci., 53, 2401–2423, http://dx.doi.org/10.1175/1520-0469(1996)053<2401:MCOTAS>2.0.CO;2.doi:10.1175/1520-0469(1996)053<2401:MCOTAS>2.0.CO;2., 1996. McFarquhar, G., Zhang, G., Poellot, M. R., Kok, G. L., McCoy, R., Tooman, T., Fridlind, A., and Heymsfield, A.: Ice properties of single-layer stratocumulus during the Mixed-Phase Arctic Cloud Experiment, 1. Observations, J. Geophys. Res., 112, D24201, http://dx.doi.org/10.1029/2007JD008633doi:10.1029/2007JD008633, 2007. McNaughtan, I. I.: The analysis of measurements of free ice and ice/water concentrations in the atmosphere of the equatorial zone. Royal Aircraft Establishment (Farnbor-ough) Technical Note No., Mech. Eng., 283, 1959. Mishchenko, M. I. and Sassen, K.: Depolarization of lidar returns by small ice crystals: An application to contrails, Geophys. Res. Lett., 25, 309–312, http://dx.doi.org/10.1029/97GL03764doi:10.1029/97GL03764, 1998. Mioche, G., Josset, D., Gayet, J.-F., Pelon, J., Garnier, A., Minikin, A., and Schwarzenboeck, A.: Validation of the CALIPSO/CALIOP extinction coefficients from in situ observations in mid-latitude cirrus clouds during CIRCLE-2 experiment, J. Geophys. Res., 115, D00H25, http://dx.doi.org/10.1029/2009JD012376doi:10.1029/2009JD012376, 2010a. Mioche G.: Validation des produits d'inversion des observations satellitaires CALIPSO et CloudSat pour la caract$\acute\rm e$risation des propri$\acute\rm e$t$\acute\rm e$s optiques et microphysiques des nuages de glace et en phase mixte, Thèse de l'Universit$\acute\rm e$ Blaise Pascal (Mars 2010), 212~pp., 2010b. Mitchell, D. L., Zhang, R., and Pitter, R. L.: Mass-dimensional relationships for ice particles and the influence of riming on snowfall rates, J. Appl. Meteorol., 29, 153–163, 1990. Platt, C. M. R., Vaughan, M. A., and Austin, R. T.: Characteristics of CALIPSO and CloudSat Backscatter at the Top Center Layers of Mesoscale Convective Systems and Relation to Cloud Microphysics, J. Appl. Meteorol. Clim., 50, 368–378, 2011. Protat, A., Pelon, J., Testud, J., Grand, N., Delville, P., Laborie, P., Vinson, J. -P., Bouniol, D., Bruneau, D., Chepfer, H., Delano\"e , J., Haeffelin, M., No\"el, V., and Tinel, C.: Le projet RALI: Combinaison d'un radar nuage et d'un lidar pour l'étude des nuages faiblement précipitants, La Météorologie, 8e série, 47, 23–33, 2004. Protat, A., Delano\"e, J., Bouniol, D., Heymsfield, A. J., Bansemer, A., and Brown, P.: Evaluation of ice water content retrievals from cloud radar reflectivity and temperature using a large airborne in situ microphysical database, J. Appl. Meteorol. Clim., 46, 557–572, 2007. Protat, A., Bouniol, D., Delano\"e, J., O'Connor, E., May, P. T., Plana-Flattori, A., Hasson, A., Görsdorf, U., and Heymsfield, A. J.: Assessment of Cloudsat Reflectivity measurements and ice cloud properties using ground-based and airborne cloud radar observations, J. Atmos. Ocean. Technol., 26, 1717–1741, 2009. Protat, A., McFarquhar, G., Um, J., and Delano\"e, J.: Obtaining best estimates for the micro physical and radiative properties of tropical ice clouds from TWP-ICE in-situ microphysical observations, J. Appl. Meteor. Clim., 50, 895–915, http://dx.doi.org/10.1175/2010JAMC2401.1doi:10.1175/2010JAMC2401.1, 2010. Sassen, K. and Zhu, J.: A global survey of CALIPSO linear depolarization ratios in ice clouds: Initial findings, J. Geophys. Res., 114, D00H07, http://dx.doi.org/10.1029/2009JD012279doi:10.1029/2009JD012279, 2009. Sassen, K., Comstock, J. M., Wang, Z., and Mace, G.: Cloud and aerosol research capabilities at FARS: The facility for atmospheric remote sensing, Bull. Am. Meteorol. Soc., 82, 1119–1138, 2001. Saunders, C. P. R. and Wahab, N. M. A.: The influence of electric fields on the aggregation of ice crystals, J. Meteorol. Soc. Jpn., 53, 121–126, 1975. Sayres, D. S., Smith, J. B., Pittman, J. V., Weinstock, E. M., Anderson, J. G., Heymsfield, G., Li, L., Fridlind, M., and Ackerman, A. S.: Validation and determination of ice water content-radar reflectivity relationships during CRYSTAL-FACE: Flight requirements for future comparisons, J. Geophys. Res., 113, D05208, http://dx.doi.org/10.1029/2007JD008847doi:10.1029/2007JD008847, 2008. Shcherbakov, V., Gayet, J.-F., Jourdan, O., Minikin, A., Ström, J., and Petzold, A.: Assessment of cirrus cloud optical and microphysical data reliability by applying statistical procedures, J. Atmos. Oceanic. Technol., 22, 409–420, 2005. Sherwood, S. C., Phillips, V. T. J., and Wettlaufer, J. S.: Small ice crystals and the climatology of lightning, Geophys. Res. Lett., 33, L05804, http://dx.doi.org/10.1029/2005GL025242doi:10.1029/2005GL025242, 2006. Stephens, G. L., Tsay, S. C., Stackhouse, P. W., and Flatau, P. J.: The relevance of the microphysical and radiative properties of cirrus clouds to climate and climatic feedback, J. Atmos. Sci., 47, 1742–1753, http://dx.doi.org/10.1175/1520-0469doi:10.1175/1520-0469, 1990. Stephens, G. L., Vane, D.G., Boain, R. J., Mace, G. G., Sassen, K., Wang, Z., Illingworth, A. J., O'Connor, E. J., Rossow, W. B., Durden, S. L., Miller, S. D., Austin, R. T., Benedetti, A., Mitrescu, C., and CloudSat Science Team: The CloudSat mission and the A-TRAIN: A new dimension to space-based observations of clouds and precipitation, Bull. Am. Meteorol. Soc., 83, 1771–1790, 2002. Stith, J. L., Dye, J., Bansemer, A., Heymsfield, A. J., Grainger, C. A., Petersen, W. A., and Ciffelli, R.: Microphysical observations of tropical clouds, J. Appl. Meteorol., 41, 97–117, 2002. Strapp, J. W., Chow, P., Maltby, M., Bezer, A. D., Korolev, A., Stromberg, I., and Hallett, J.: Cloud microphysical measurements in thunderstorm outflow regions during Allied/BAe 1997 flight trials, 37th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV., 11–14 Jan 1999, AIAA 99-0498, 1999. Wahab, N. M. A.: Ice crystal interactions in electric fields, PhD thesis, UMIST, 1974. Winker, D. M., Pelon, J., and McCormick, M. P.: The CALIPSO mission: Spaceborne lidar for observation of aerosols and clouds, Status and Performance, Proceedings of SPIE, 4893, 1–11, 2003. Winker, D. M., Pelon, J., Coakley Jr., J. A., Ackerman, S. A., Charlson, R. J., Colarco, P. R., Flamant, P., Fu, Q., Hoff, R., Kittaka, C., Kubar, T. L., LeTreut, H., McCormick, M. P., Megie, G., Poole, L., Powell, K., Trepte, C., Vaughan, M. A., Wielicki, B. A.: The CALIPSO Mission: A Global 3-D View Of Aerosols And Clouds, Bull. Am. Meteorol. Soc., 91, 1211–1229, http://dx.doi.org/10.1175/2010BAMS3009.1doi:10.1175/2010BAMS3009.1, 2010. Wirth, M., Fix, A., Mahnke, P., Schwarzer, H., Schrandt, F., and Ehret, G.: The airborne multi-wavelength water vapor differential absorption lidar WALES: system design and performance, Appl. Phys. B, 96, 201–213, http://dx.doi.org/10.1007/s00340-009-3365-7doi:10.1007/s00340-009-3365-7, 2009.