A New Classification of In Situ and Anvil Cirrus Clouds Uncovers Their Properties and Interhemispheric Connections

Abstract The challenge of distinguishing convective anvil cirrus from in situ cirrus has long limited the quantification of their distinct roles in regulating upper‐tropospheric moisture and modulating Earth's energy budget. In this study, we address this ambiguity by introducing a physically constrained classification framework that applies advanced computer vision techniques to CloudSat‐CALIPSO observations. By tracking the complete physical evolution of cloud systems from their convective origins, this method enables a robust global separation of anvil and in situ cirrus. Our results illuminate stark contrasts in their macro‐ and micro‐properties, governed by fundamentally different mechanisms. Anvil cirrus extent is tightly coupled to dynamic factors, whereas in situ cirrus, while linked to local tropopause thermodynamics, exhibits strong modulation by remote atmospheric influences from the opposite hemisphere. This identified linkage shows a previously unrecognized interhemispheric teleconnection: wherein large‐scale deep convective systems in one hemisphere rapidly influence in situ cirrus formation in the other. We hypothesize that this coupling is mediated by planetary‐scale waves—likely fast‐propagating Kelvin waves that transmit energy across the equator, cooling the remote tropical tropopause layer, with subsequent interactions with the subtropical jet fostering mid‐latitude in situ development. This newly quantified atmospheric coupling provides a pathway for improving representation of cirrus in climate models and suggests a mechanism by which regional shifts in convection under global warming could reshape global cirrus distributions and their radiative impact.