Secondary Ice Formation Process in Cirrus; A Simulation Study

Experimental observations indicate that secondary atmospheric ice formation can occur on ice surfaces in the cirrus cloud regime. The secondary nucleation can be triggered by various factors such as mechanical disturbances, temperature changes, or specific surface characteristics. Notably, experimental findings suggest that secondary nucleation is more likely to initiate at cracks and edges on the sublimating ice crystal surface, emphasizing the critical role of surface defects. We hypothesize that the surface features, including cracks, edges, and rough edges, on pre-existing ice can also provide favorable sites for nucleation due to localized high energy and increased vapor concentration.

However, monitoring this process at short spatiotemporal scales is experimentally challenging. To address this, we employ molecular-scale simulations to study secondary nucleation behavior with high resolution over a wide range of cirrus temperatures and ambient pressures.

To examine our hypothesis, we investigate nucleation on flat, convex, and concave surfaces to understand the effect of surface roughness on ice nucleation. Since all types of roughness can be represented by combinations of convex and concave surfaces, this approach provides a comprehensive and generalized insight into the impact of surface roughness on nucleation. Beside, the ice nucleation on the convex surface provide us insight about nucleation on nanoparticles. Although limitations in computational resources may prevent us from modeling micro-sized ice-crystals with small curvatures, our simulations still provide qualitative insights into the impact of surface curvature on ice nucleation. Furthermore, we model ice nucleation of water vapor under confinement, exploring scenarios where water vapor trapped in small cracks or between ice crystals can lead to localized supersaturation, thereby promoting nucleation at these confined sites. Our preliminary results suggest that secondary ice nucleation exhibits different dynamics under varying levels of confinement.

By combining these approaches, our study offers a deeper understanding of the mechanisms driving secondary ice nucleation and the role of surface characteristics in this complex process.