How big should hexagonal ice crystals be to produce halos?

It has been hypothesized that the frequent lack of halos in observations of cirrus and contrails and laboratory measurements is caused by small ice crystal sizes that put the particles outside the geometrical optics domain of size parameters. We test this hypothesis by exploiting a strong similarity of ray tracing phase functions for finite hexagonal and circular ice cylinders and using T-matrix computations of electromagnetic scattering by circular cylinders with size parameters up to 180 in the visible. We conclude that well-defined halos should be observable for ice crystal size parameters of the order of 100 and larger and discuss remote-sensing implications of this result.

[1]  J. Foot,et al.  Some observations of the optical properties of clouds. II: Cirrus , 1988 .

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

[3]  Patrick Minnis,et al.  Inference of Cirrus Cloud Properties Using Satellite-observed Visible and Infrared Radiances. Part II: Verification of Theoretical Cirrus Radiative Properties , 1993 .

[4]  J. Hansen,et al.  Light scattering in planetary atmospheres , 1974 .

[5]  Robert G. Greenler,et al.  Rainbows, halos, and glories , 1980 .

[6]  M. Mishchenko,et al.  Reprint of: T-matrix computations of light scattering by nonspherical particles: a review , 1996 .

[7]  Yoshihide Takano,et al.  Radiative Transfer in Cirrus Clouds. Part III: Light Scattering by Irregular Ice Crystals , 1995 .

[8]  M. Mishchenko,et al.  Applicability of regular particle shapes in light scattering calculations for atmospheric ice particles. , 1996, Applied optics.

[9]  Kenneth Sassen,et al.  Contrail-Cirrus and Their Potential for Regional Climate Change , 1997 .

[10]  P. Francis,et al.  The retrieval of cirrus cloud properties from aircraft multi‐spectral reflectance measurements during EUCREX'93 , 1998 .

[11]  Optical and microphysical properties of a cold cirrus cloud : Evidence for regions of small ice particles. , 1989 .

[12]  Patrick Minnis,et al.  Inference of cirrus cloud properties using satellite-observed visible and infrared radiances. Part I: parameterization of radiance fields , 1993 .

[13]  K. Liou,et al.  Solar Radiative Transfer in Cirrus Clouds. Part I: Single-Scattering and Optical Properties of Hexagonal Ice Crystals , 1989 .

[14]  K. Rockwitz.  Scattering properties of horizontally oriented ice crystal columns in cirrus clouds. Part 1. , 1989, Applied optics.

[15]  William R. Thursby,et al.  Light Scattering by Ice Crystals , 1969 .

[16]  J. Buriez,et al.  POLDER observations of cloud bidirectional reflectances compared to a plane-parallel model using the International Satellite Cloud Climatology Project cloud phase functions , 1998 .

[17]  Kenneth Sassen,et al.  Remote Sensing of Planar Ice Crystal Fall Attitudes , 1980 .

[18]  M. Poellot,et al.  Role of small ice crystals in radiative properties of cirrus: a case study , 1994 .

[19]  J. Spinhirne,et al.  Cirrus infrared parameters and shortwave reflectance relations from observations , 1996 .

[20]  S. Warren,et al.  Optical constants of ice from the ultraviolet to the microwave. , 1984, Applied optics.

[21]  W. V. Hoyningen-Huene,et al.  Information about scattering properties and particle characteristics of a stratiform cloud at Helgoland by remote optical measurements , 1995 .

[22]  Harumi Isaka,et al.  Scattering Phase Function of Bullet Rosette Ice Crystals , 1995 .

[23]  Tara L. Jensen,et al.  Shapes, sizes and light scattering properties of ice crystals in cirrus and a persistent contrail during SUCCESS , 1998 .

[24]  A. Macke,et al.  Scattering of light by polyhedral ice crystals. , 1993, Applied optics.

[25]  Effects of ice-crystal structure on halo formation: cirrus cloud experimental and ray-tracing modeling studies. , 1994, Applied optics.

[26]  Cirrus properties deduced from CO2 lidar observations of zenith-enhanced backscatter from oriented crystals , 1993 .

[27]  H. Chepfer,et al.  Cirrus clouds’ microphysical properties deduced from POLDER observations , 1998 .

[28]  P. Marston.  1 - Geometrical and Catastrophe Optics Methods in Scattering , 1992 .

[29]  P. Francis.  Some Aircraft Observations of the Scattering Properties of Ice Crystals , 1995 .

[30]  M. Mishchenko,et al.  Modeling phase functions for dustlike tropospheric aerosols using a shape mixture of randomly oriented polydisperse spheroids , 1997 .

[31]  Andrew A. Lacis,et al.  Sensitivity of cirrus cloud albedo, bidirectional reflectance and optical thickness retrieval accuracy to ice particle shape , 1996 .

[32]  N. L. Abshire,et al.  Some Microphysical Properties of an Ice Cloud from Lidar Observation of Horizontally Oriented Crystals , 1978 .

[33]  K. Liou,et al.  Single-scattering properties of complex ice crystals in terrestrial atmosphere , 1998 .

[34]  Kenneth Sassen,et al.  Scattering of Polarized Laser Light by Water Droplet, Mixed-Phase and Ice Crystal Clouds. Part I: Angular Scattering Patterns , 1979 .

[35]  J. Klett.  Orientation Model for Particles in Turbulence , 1995 .

[36]  O. Crepel,et al.  A new airborne Polar Nephelometer for the measurement of optical and microphysical cloud properties. Part II: Preliminary tests , 1997 .