Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments

Abstract. We report on the development and test results of the new optical particle counter TOPS-Ice (Thermo-stabilized Optical Particle Spectrometer for the detection of Ice). The instrument uses measurements of the cross-polarized scattered light by single particles into the near-forward direction (42.5° ± 12.7°) to distinguish between spherical and non-spherical particles. This approach allows the differentiation between liquid water droplets (spherical) and ice particles (non-spherical) having similar volume-equivalent sizes and therefore can be used to determine the fraction of frozen droplets in a typical immersion freezing experiment. We show that the numerical simulation of the light scattered on non-spherical particles (spheroids in random orientation) considering the actual scattering geometry used in the instrument supports the validity of the approach, even though the cross-polarized component of the light scattered by spherical droplets does not vanish in this scattering angle. For the separation of the ice particle mode from the liquid droplet mode, we use the width of the pulse detected in the depolarization channel instead of the pulse height. Exploiting the intrinsic relationship between pulse height and pulse width for Gaussian pulses allows us to calculate the fraction of frozen droplets even if the liquid droplet mode dominates the particle ensemble. We present test results obtained with TOPS-Ice in the immersion freezing experiments at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator) and demonstrate the excellent agreement with the data obtained in similar experiments with a different optical instrument. Finally, the advantages of using the cross-polarized light measurements for the differentiation of liquid and frozen droplets in the realistic immersion freezing experiments are discussed.

[1]  K. Liou,et al.  Finite-difference time domain method for light scattering by small ice crystals in three-dimensional space , 1996 .

[2]  U. Lohmann,et al.  Single ice crystal measurements during nucleation experiments with the depolarization detector IODE , 2008 .

[3]  K. Sassen.  The Polarization Lidar Technique for Cloud Research: A Review and Current Assessment , 1991 .

[4]  U. Lohmann,et al.  The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds , 2010 .

[5]  Jen-Ping Chen,et al.  A Classical-Theory-Based Parameterization of Heterogeneous Ice Nucleation by Mineral Dust, Soot, and Biological Particles in a Global Climate Model , 2010 .

[6]  A. Macke,et al.  Single Scattering Properties of Atmospheric Ice Crystals , 1996 .

[7]  J. Voigtländer,et al.  Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies , 2011 .

[8]  Tom Rother,et al.  Electromagnetic Wave Scattering on Nonspherical Particles: Basic Methodology and Simulations , 2010 .

[9]  M. Petters,et al.  Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles , 2011 .

[10]  A. Heymsfield,et al.  PRODUCTION OF ICE IN TROPOSPHERIC CLOUDS A Review , 2005 .

[11]  J. Hovenier,et al.  Depolarization of light backscattered by randomly oriented nonspherical particles. , 1995, Optics letters.

[12]  Joshua A. Gordon,et al.  Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC , 2010 .

[13]  A. Ansmann,et al.  Vertical profiling of convective dust plumes in southern Morocco during SAMUM , 2009 .

[14]  W. Steen.  Absorption and Scattering of Light by Small Particles , 1999 .

[15]  K Umashankar,et al.  CHAPTER 6 – Finite-Difference Time Domain Method , 1999 .

[16]  H. Jonsson,et al.  The cloud, aerosol and precipitation spectrometer: a new instrument for cloud investigations , 2001 .

[17]  Jonathan P. Taylor,et al.  Airborne instruments to measure atmospheric aerosol particles, clouds and radiation: A cook's tour of mature and emerging technology , 2011 .

[18]  Martin Gallagher,et al.  Studies of heterogeneous freezing by three different desert dust samples , 2009 .

[19]  M. Bailey,et al.  A Comprehensive Habit Diagram for Atmospheric Ice Crystals: Confirmation from the Laboratory, AIRS II, and Other Field Studies , 2009 .

[20]  M. Shupe,et al.  Evidence of liquid dependent ice nucleation in high‐latitude stratiform clouds from surface remote sensors , 2011 .

[21]  J. Klett,et al.  Microphysics of Clouds and Precipitation , 1978, Nature.

[22]  H. V. Hulst.  Light Scattering by Small Particles , 1957 .

[23]  S. Brooks,et al.  A new method for measuring optical scattering properties of atmospherically relevant dusts using the Cloud and Aerosol Spectrometer with Polarization (CASPOL) , 2013 .

[24]  P. Yang,et al.  Calculation of the single-scattering properties of randomly oriented hexagonal ice columns: a comparison of the T-matrix and the finite-difference time-domain methods. , 2001, Applied optics.

[25]  R. Jaenicke,et al.  The fast Ice Nucleus chamber FINCH , 2008 .

[26]  S. Brooks,et al.  A new method for measuring optical scattering properties of atmospherically relevant dusts using the Cloud Aerosol Spectrometer Polarization (CASPOL) instrument , 2012 .

[27]  Heterogeneous freezing of droplets with immersed mineral dust particles – measurements and parameterization , 2009 .

[28]  B. Draine,et al.  Discrete-Dipole Approximation For Scattering Calculations , 1994 .

[29]  W. Cooper,et al.  Field Evidence Supporting Quantitative Predictions of Secondary Ice Production Rates , 1987 .

[30]  Ping Yang,et al.  Sensitivity of the backscattering Mueller matrix to particle shape and thermodynamic phase. , 2003, Applied optics.

[31]  Michael I. Mishchenko,et al.  Depolarization of lidar returns by small ice crystals: An application to contrails , 1998 .

[32]  F. Stratmann,et al.  White-light optical particle spectrometer for in situ measurements of condensational growth of aerosol particles. , 2005, Applied optics.

[33]  M. Mishchenko,et al.  Scattering properties of needlelike and platelike ice spheroids with moderate size parameters. , 2000, Applied optics.

[34]  M. Schnaiter,et al.  Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals – cloud chamber measurements in the context of contrail and cirrus microphysics , 2012 .

[35]  M. Hartmann,et al.  Light scattering by small particles. Von H. C. VANDE HULST. New York: Dover Publications, Inc. 1981. Paperback, 470 S., 103 Abb. und 46 Tab., US $ 7.50 , 1984 .

[36]  Albert Ansmann,et al.  Saharan dust and heterogeneous ice formation : Eleven years of cloud observations at a central European EARLINET site , 2010 .

[37]  D. Rogers.  Development of a continuous flow thermal gradient diffusion chamber for ice nucleation studies , 1988 .

[38]  R. Engelmann,et al.  Evolution of the ice phase in tropical altocumulus: SAMUM lidar observations over Cape Verde , 2009 .

[39]  M. Schnaiter,et al.  Circular depolarization ratios of single water droplets and finite ice circular cylinders: a modeling study , 2011 .

[40]  Tom Rother,et al.  Electromagnetic Wave Scattering on Nonspherical Particles , 2009 .

[41]  U. Lohmann,et al.  The Zurich Ice Nucleation Chamber (ZINC)-A New Instrument to Investigate Atmospheric Ice Formation , 2008 .

[42]  Albert Ansmann,et al.  Influence of Saharan dust on cloud glaciation in southern Morocco during the Saharan Mineral Dust Experiment , 2008 .

[43]  M. Wendisch,et al.  Minimizing Instrumental Broadening of the Drop Size Distribution with the M-Fast-FSSP , 2004 .

[44]  C. Linke,et al.  A review of optical measurements at the aerosol and cloud chamber AIDA , 2009 .

[45]  G. McFarquhar,et al.  Ice nuclei characteristics from M‐PACE and their relation to ice formation in clouds , 2009 .

[46]  Laboratory Studies and Numerical Simulations of Cloud Droplet Formation under Realistic Supersaturation Conditions , 2004 .

[47]  Y. Takano,et al.  Scattering phase matrix for hexagonal ice crystals computed from ray optics. , 1985, Applied optics.

[48]  Thomas Wriedt,et al.  New Scattering Information Portal for the light-scattering community , 2008 .