Investigating ice formation pathways in satellite-observed cirrus clouds using Lagrangian microphysical modelling

Understanding the formation mechanisms of ice clouds is challenging due to their complex composition and diverse growth processes. Observational constraints have historically been limited, resulting in significant gaps in our understanding and representation of ice clouds. Satellite measurements are particularly limited by the absence of critical environmental context information needed to identify cloud formation mechanisms and evolution. These observations provide only a snapshot of cloud states and their microphysical properties at a single moment. This study seeks to overcome these limitations by incorporating additional metrics on ice cloud history and origin alongside operational satellite products.

We introduce a novel framework that combines satellite observations with Lagrangian transport and ice microphysical modelling to provide insights into the history and origin of air parcels contributing to ice cloud formation. The Chemical LAgrangian Model of the Stratosphere (CLaMS) is employed to trace air parcel trajectories along the DARDAR-Nice track. Additionally, the CLaMS-Ice model is used to simulate cirrus clouds along these trajectories, offering metrics on cirrus age, origin (in situ vs. liquid-origin), and ice formation pathways (heterogeneous vs. homogeneous nucleation) that can be associated with satellite observations.

To illustrate this approach, we present three case studies representative of distinct mid-latitude synoptic conditions: fast updraft, slow updraft, and orographically driven ice clouds. These cases demonstrate an in-depth analysis of air parcel evolution since cirrus formation, followed by a statistical examination of the relationship between microphysical properties and the origin-based metrics. Furthermore, the method is evaluated by comparing modeled microphysics with satellite retrievals. A sensitivity analysis is conducted to assess the impact of input parameters in CLaMS-Ice, including small-scale temperature fluctuations, environmental ice-nucleating particle (INP) concentrations, and sedimentation parameterizations. Overall, this comprehensive approach enhances our understanding of ice cloud processes, provides valuable context for interpreting satellite observations, and contributes to refining the representation of cirrus clouds in atmospheric models.