Both atmospheric ice and mineral dust are considered to play important roles in our climate system through their impacts on the radiative energy budget. These impacts depend on the size, shape, composition and concentration of the ice and dust particles. However, the non-spherical shape of these particles yields uncertainties in our understanding how they interact with radiation. One of the main aims of this work is to better understand the impacts of particle size-shape distributions on radiative effects of ice and dust. For dust particles, the overall goal is to improve the treatment of optical properties of dust in global aerosol-climate models. In this thesis, the solar radiative effects of variously sized and shaped ice and dust particles are simulated using radiative transfer models. In addition, a global aerosol–climate model is used to investigate the impact of dust particle nonsphericity. Different radiative transfer models, atmospheric and surface properties etc. are used, based on the requirements of each study. Size-shape distributions of ice clouds are based on in-situ measurements, whereas for dust, carefully validated shape models of spheroids are used. This thesis offers a broad outlook on the effects of ice clouds on solar irradiances and on the angular dependence of the circumsolar radiance. In addition, it offers interesting new insight into the connections between particle morphology, cloud microphysics and cloud radiative effects. It is found that solar radiation is sensitive to the concentration of small ice crystals. In addition, comparison of simulated and measured radiation in the presence of ice clouds suggests that most natural ice crystals are not pristine, but can either have some surface roughness or other non-idealities in their shape. The results reveal that the use of spheroidal shape distributions has only small or moderate impacts on regional and global-scale direct radiative effects of dust. Consistent with this, experiments with a global aerosol–climate model indicate that the assumption of spherical shape for dust particles is not a considerable error source in climate simulations. Most probably, however, this conclusion cannot be extended to remote sensing applications.
|Myöntöpäivämäärä||2 kesäkuuta 2017|
|Tila||Julkaistu - 2 kesäkuuta 2017|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|
- 114 Fysiikka