Bifurcation and Stability of the Co‐Condensation Dynamics of H ₂ SO ₄ ‐H ₂ O Droplets in Venusian Clouds

Abstract The clouds covering Venus globally, that are primarily composed of ‐O droplets, strongly influence the thermal structure and dynamics of the atmosphere. However, the mechanism governing their growth and long‐term maintenance remains poorly understood. In this study, the bifurcation structure of the droplets' growth dynamics through the co‐condensation of O and is investigated by constructing a box model under the assumption of a monodisperse droplet population. Our analysis reveals that the phase portrait which is a diagram with the masses of O and liquids in the droplet as the axes, showing how each evolves over time, depends on the saturation ratios of the O and gases and that the mass of O in the droplet varies much more rapidly than that of under conditions near the Venusian cloud base. The condition for the stable existence of Venusian cloud droplets is also investigated in terms of the saddle‐node bifurcation. Based on these findings, we simulate the droplets' growth under the thermodynamic conditions near the Venusian cloud base and find that the small cloud droplets, such as Mode 1, may rapidly grow into larger ones, such as Modes 2 or 3, depending on the droplet number density.