Classification of Fog Life Cycle Phases Using Ground-based and Satellite-based Observations

A complete understanding of the fog life cycle — defined as formation, maturity, and dissipation phases — provides a basis for better predictions of fog formation and dissipation. While satellites can observe fog and low stratus (FLS) over a large spatial extent, ground-based instruments provide more detailed vertical and temporal information about fog at specific locations. 
In this study, we classify the life cycle phases of radiation fog events in autumn 2009-2015 at a ground station in Southwest Germany by combining geostationary satellite observations with ceilometer and in-situ measurements. For this, we develop a life cycle phase classification algorithm that automatically detects the start and end times of each phase based on visibility trends and thresholds. Unlike other methodologies, we define fog events not only through a visibility threshold of 1000 m but also by the processes involved during fog formation and dissipation. These processes are identified through changes in visibility trends and values and validated against backscatter patterns. Furthermore, we demonstrate that ground-based visibility effectively detects radiation fog phases, while its combination with ceilometer data has the potential to detect the life cycle phases of cloud base lowering fog events. Thus, combining these data sources is essential for effectively detecting the life cycle phases of different fog types. Additionally, we find that ground-based data performs better in phase detection at individual locations compared to a satellite-based FLS life cycle dataset. Consequently, we propose that future satellite-based FLS detection methods incorporate an assessment of the changes in the spectral signals of FLS throughout its life cycle for a more detailed phase characterization over large regions.