Unraveling ice multiplication in winter orographic clouds via in-situ observations, remote sensing and modeling.

Recent years have shown that secondary ice production (SIP) is ubiquitous, affecting all clouds from polar to tropical regions. SIP is not described well in models and may explain biases in warm mixed-phase cloud ice content and structure. Through modeling constrained by in-situ observations and its synergy with radar we show that SIP in orographic clouds exert a profound impact on the vertical distribution of hydrometeors and precipitation, especially in seeder-feeder cloud configurations. The mesoscale model simulations coupled with a radar simulator strongly support that enhanced aggregation and SIP through ice-ice collisions contribute to observed spectral bimodalities, skewing the Doppler spectra toward the slower-falling side at temperatures within the dendritic growth layer, ranging from -20 °C to -10 °C. This unique signature provides an opportunity to infer long-term SIP occurrences from the global cloud radar data archive, particularly for this underexplored temperature regime.

Effect of macromolecular architecture on the self-assembly behavior of copolymers in a selective polymer host.

We present a detailed simulation study of the structural and dynamical behavior of star-shaped mikto-arm (polystyrene)8(poly(ethylene oxide))8, (PS)8(PEO)8, copolymers with eight arms of each type, versus that of a linear polystyrene-block-poly(ethylene oxide), PS-b-PEO, diblock, in a selective homopolymer host. Both copolymers are blended at the same weight fraction 33% with an oligomeric PEO host. We use atomistic molecular dynamics simulations to account for the molecular interactions present in the blends and to study quantitatively the dynamical and structural properties of these systems. The presence of the selective oligomeric PEO host leads to the formation of complex self-assembled structures. While cylindrical structures are formed in the case of linear diblock copolymers, mikto-arm star copolymers form percolated interconnected assemblies within the PEO host. The cylindrical objects formed by the linear diblock copolymers exhibit a higher degree of compactness and a weaker temperature dependence than the percolated network formed by their star-shaped analogues. The dynamics is governed primarily by the local structural heterogeneity, i.e., the environment around a segment, which is determined by the interaction between the different components, the macromolecular architecture of the copolymer as well as the associated geometrical constrains. Our data further stress the fact that the structural and dynamical properties in these blends may be controlled/tuned by the macromolecular architecture of the copolymer and/or by adjusting the temperature.