Evaluation of Ice Microphysics Parameterizations with mm- and sub-mm Radiometry

The majority of precipitation on earth originates in the ice phase, and ice clouds play an important role in regulating the earth's energy budget. At any given time, ice clouds cover 25-30% of the Earth, making them important contributors to data assimilated at wavelengths affected by clouds. For these reasons, improving the modeling of the microphysical processes occurring within these clouds is critical to weather and climate prediction.

Remote sensing is an important tool to augment in-situ (aircraft) observations of ice clouds by providing large-scale and temporal context and global observations. In particular, passive mm-wave and submm-wave radiometry (frequencies from 150-880 GHz) fills the gap between traditional microwave (<150 GHz) observations, which are sensitive to ice water paths > 1 kg/m², and visible/infrared observations, which are sensitive to cloud top properties for all but optically thin clouds. Sub-mm sensors require smaller apertures than microwave sensors of the same resolution and are thus attractive for small (CubeSat) platforms and/or distributed measurements. Motivated by these needs, future satellite measurements, and inspired by recent work utilizing the polarized 166-GHz radiances observed by GMI, we have pursued several improvements to satellite simulation capabilities that allow the exploration of pathways to evaluate ice microphysics parameterizations with mm and sub-mm observations, including state-of the art scattering models for:

- realistic aggregates and rimed particles up to 5mm equivalent diameter

- preferentially-oriented, idealized shapes with observed size-aspect ratio relationships

Simulations of idealized single-cell and organized convection are used to demonstrate the information content in measurements at sub-mm frequencies. In particular, we note that the polarized measurements are useful for constraining the vertically integrated mass fraction of oriented ice particles, whereas differential scattering at frequencies with similar clear-sky weighting functions (e.g., near the 183 and 325 GHz H₂O absorption lines) can constrain particle density. By altering process rates in the Morrison (2009) microphysics scheme, the water content in each ice class is altered and observed multi-channel radiance pdfs can be more realistically simulated.