The energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth’s energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 μm. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at σ = 0.1 to severely rough at σ = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75.

Small water ice crystals are the main component of cold tropospheric clouds such as cirrus. Because these clouds cover large areas of our planet, their role in the radiation budget of incoming and outgoing radiation to the planet's surface is important. At present, the representation of these clouds in climate and weather models is subject to improvements: a large part of the uncertainty error stems from the lack of precise micro-physical and radiation model schemes for ice crystal clouds. To improve the cloud representations, a better understanding of the life time dynamics of the clouds and their composition is necessary, comprising a detailed understanding of the ice particle genesis, and development over their lifetime. It is especially important to understand how the development of ice crystals over time is linked to the changes in observable variables such as water vapour content and temperature and how they change the light scattering properties of the crystals. Recent remote and aircraft based in-situ measurements have shown that many ice particles show a light scattering behaviour typical for crystals having rough surfaces or being of complex geometrical shapes. The aim of this thesis was to develop the experimental setup and experiments to investigate this further by studying the surface morphology of small water ice crystals using scanning electron microscopy (SEM). The experiments I developed study the growth of water ice crystals inside an SEM chamber under controlled environmental conditions. The influence of water vapour supersaturation, pressure and temperature is investigated. I demonstrate how to retrieve the surface topology from observed crystals for use as input to computational light scattering codes to derive light scattering phase functions and asymmetry parameters, which can be used as input into atmospheric models. Difficulties with the method for studying the growth of water ice crystals, such as the effect of the electron beam-gas ionization and charging effects, the problem of facilitating repeated and localized ice growth, and the effect of radiative influences on the crystal growth are discussed. A broad set of nucleation target materials is studied. In a conclusion, I demonstrate that the method is suitable to study the surface morphologies, but is experimentally very challenging and many precautions must be taken, such as imaging only once and preventing radiative heat exchange between the chamber walls and the crystals to avoid unwanted effects on the crystal morphology. It is also left as a question if a laboratory experiment, where crystals will need to be grown in connection to a substrate, can represent the real world well enough. Deriving the required light scattering data in-situ might be an alternative, easier way to collect data for modelling use.

This thesis examines the role of remote sensing technology in providing information to northern residents of Kugluktuk and Cambridge Bay, Kitikmeot region of Nunavut, Western Canadian Arctic, for the purpose of improving sea ice trafficability and safety. The main objectives of this thesis include 1) the identification of northern community sea ice information needs that can be addressed using remote sensing, and 2) the creation of remote sensing-based products showing sea ice surface roughness information useful to community sea ice trafficability and safety. Thesis outcomes include the refinement and dissemination of information and products with these communities. Research methods involved interviews with northern community members that were analysed using thematic analysis, as well as quantitative assessments of sea ice roughness using satellite datasets. Maps of sea ice surface roughness were created using Sentinel-1 synthetic aperture radar and the Multi-angle Imaging Spectroradiometer, and were evaluated against fine-scale airborne LiDAR data. / Graduate / 2020-07-31