Download or read book Surface Kinetic Effects on Ice Nucleation in Cirrus Clouds written by Benjamin Sherman and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In-situ measurements suggest that heterogeneous nucleation is the dominant ice formation mechanism in the upper atmosphere. Clouds formed heterogeneously typically contain lower ice concentrations and larger crystals than those formed homogeneously. Because heterogeneous ice formation occurs at lower ice supersaturations than homogeneous freezing of supercooled drops, sufficient heterogeneous freezing can suppress or eliminate the homogeneous freezing process. The difference in freezing process may significantly alter the radiative properties of and particle sedimentation rates from cirriform clouds. The underlying physical processes influencing the competition between heterogeneous and homogeneous nucleation remain poorly understood. One such process that may be of importance is surface kinetic resistance to ice vapor growth and its dependence on particle shape evolution, which is investigated in this thesis using the Kinetically Limited Adaptive Habit (KLAH) growth method in a Lagrangian parcel model framework.The KLAH model predicts axis-dependent growth efficiencies that allow for particle shape to evolve in time. After nucleation, ice particles become increasingly less isometric as they grow. This non-linearly increases the vapor flux to the semi-major axis, increasing the rate at which vapor is depleted from the ambient environment. We show that, in some cases, more surface resistance may in fact accelerate this increase in the growth rate. As a result, fewer heterogeneously-nucleated ice crystals are required to suppress homogeneous nucleation. This may help to explain the relative dominance of heterogeneous nucleation in the upper atmosphere. Furthermore, we show that simpler treatments of surface kinetics are unable to capture this effect, and may lead to both over- and under-predictions of ice concentration while also missing the evolution of ice particle shape that occurs above the cloud-base nucleation zone.