Ice Cloud Bulk Scattering Property Models From 0.2 to 100 μm

Ice cloud bulk single-scattering property models are necessary to simulate radiances at the top of the atmosphere, within the atmosphere, and at the surface. These models are also essential for broadband radiative transfer simulations necessary for assessing ice cloud radiative forcing. For remote sensing purposes, our goal has been to develop models that maximize the consistency between various active and passive sensors in the NASA A-Train constellation. We have developed bulk scattering models at 445 discrete wavelengths between 0.2 μm and 100 μm for pure ice clouds, i.e., clouds with no contamination from heavy aerosol events. The models are based on microphysical data from eleven field campaigns using a variety of in situ probes; the 2D (and similar) probe data are corrected to mitigate the impact of ice particles that shatter at the probe inlets. A library of the ice particle single-scattering properties is available for plates, droxtals, hollow and solid columns, hollow and solid bullet rosettes, an aggregate of solid columns, and a small/large aggregate of plates. Particle surface texture, i.e., surface roughness, is considered in the optical properties of ice particles. Two sets of models are developed that assume the use of an individual habit only (solid columns and the aggregate of solid columns), and a third set is based on a general habit mixture that incorporates all nine habits. While the general habit mixture provides consistency with in situ microphysical measurements and the closest agreement with polarized reflectivities observed by the POLDER instrument on the PARASOL satellite, the aggregate of severely–roughened solid columns provides the closest agreement between solar and infrared optical thicknesses.

While our work to date has focused on “pure” ice clouds, we are now turning attention to events where the ice clouds become contaminated with absorbing aerosols from severe fires that become pyroconvective. When a fire becomes pyroconvective, large quantities of absorbing aerosols are injected into the upper troposphere and often penetrate briefly into the stratosphere. Once at high altitudes, the heavy aerosol plumes can travel thousands of kilometers from the source region very quickly. Over the past year, we have captured a number of pyroconvection events in which smoke plumes directly impact existing ice clouds. As part of this presentation, we will summarize work regarding both pure and contaminated ice clouds.