Abstract. Microwave (1–300 GHz) dual-polarization
measurements above 100 GHz are so far sparse, but they
consistently show polarized scattering signals of ice clouds. Existing
scattering databases of realistically shaped ice crystals for microwaves
and submillimeter waves (>300 GHz) typically assume total
random orientation, which cannot explain the polarized signals. Conceptual
models show that the polarization signals are caused by oriented ice
particles. Only a few works that consider oriented ice crystals exist,
but they are limited to microwaves only. Assuming azimuthally randomly
oriented ice particles with a fixed but arbitrary tilt angle, we produced
scattering data for two particle habits (51 hexagonal plates and
18 plate aggregates), 35 frequencies between 1
and 864 GHz, and 3 temperatures (190, 230
and 270 K). In general, the scattering data of azimuthally randomly
oriented particles depend on the incidence angle and two
scattering angles, in contrast to total random orientation, which depends
on a single angle. The additional tilt angle further increases the
complexity. The simulations are based on the discrete dipole approximation
in combination with a self-developed orientation averaging approach.
The scattering data are publicly available from Zenodo (https://doi.org/10.5281/zenodo.3463003).
This effort is also an essential part of preparing for the upcoming
Ice Cloud Imager (ICI) that will perform polarized observations at
243 and 664 GHz. Using our scattering data
radiative transfer simulations with two liquid hydrometeor species
and four frozen hydrometeor species of polarized Global
Precipitation Measurement (GPM) Microwave Imager (GMI) observations at 166 GHz
were conducted. The simulations recreate the observed polarization
patterns. For slightly fluttering snow and ice particles, the simulations
show polarization differences up to 11 K using plate aggregates
for snow, hexagonal plates for cloud ice and totally randomly oriented
particles for the remaining species. Simulations using strongly fluttering
hexagonal plates for snow and ice show similar polarization signals.
Orientation, shape and the hydrometeor composition affect the polarization.
Ignoring orientation can cause a negative bias for vertically polarized
observations and a positive bias for horizontally polarized observations.
Microwave and submillimeter wave scattering of oriented ice particles
