Noctilucent Clouds Polarimetry: Twilight Measurements in a Wide Range of Scattering Angles

TL;DR

This study measures the polarization of twilight sky light affected by noctilucent clouds over Russia, using wide-angle observations to infer particle sizes through comparison with simulations.

Contribution

It introduces a method for separating cloud scattering from twilight background and estimates ice particle sizes using polarization data and T-matrix modeling.

Findings

Particle size estimated at 0.06 microns

Maximum particle radius about 0.1 microns

Polarization dependence sensitive to particle size

Abstract

Wide-field polarization measurements of the twilight sky background during the several nights with bright and extended noctilucent clouds in central and northern Russia in 2014 and 2015 are used to build the phase dependence of degree of polarization of sunlight scattered by clouds particles in a wide range of scattering angles (from 40 to 130 degrees). This range covers the linear polarization maximum near 90 degrees and large-angle slope of the curve which are most sensitive to the particle size. The method of separation of scattering on clouds particles on the twilight background is presented. Results are compared with T-matrix simulations for different sizes and shapes of ice particles, the best-fit model radius of particles (0.06 microns) and maximum radius (about 0.1 microns) are estimated.