title: Polarimetry of a 22 degrees halo.
abstract: The linear polarization and intensity of a 22 degrees halo has been measured simultaneously at seven wavelengths as a function of scattering angle. The polarization pattern is found to be dominated by a narrow peak centered at the halo angle. The amount of polarization in this peak is much higher than expected from Fresnel refraction alone. The observations are explained with a birefringence-diffraction halo polarization model. The effective diameter of the hexagonal face of the halo-generating crystals is found to be 41 and 54 microm for two separate scans. An independent single-wavelength parhelion observation indicates a stronger birefringence peak concentrated in an even smaller angular scattering range and a crystal diameter of 220 microm. Crystal sizes derived from the halo intensity distributions are found to be consistent with those obtained from polarization. The data demonstrate the power of halo polarimetry as a tool for detection and identification of birefringent crystals in terrestrial or extraterrestrial atmospheres.
authors: G P
authors: GP
authors: Können
authors: J
authors: J
authors: Tinbergen