| 16 Apr 2026
The evolution of cloud microphysical properties during Cold Air Outbreaks – a composite approach to in situ measurements
Abstract. When cold, dry polar air is advected over a warmer ocean, a rapid development of clouds is observed. Several airborne field campaigns have been dedicated to these marine Cold Air Outbreaks (mCAOs). However, their properties, as well as their impact on the energy budget and water cycle, remains poorly understood. This study investigates the evolution of cloud microphysics during mCAOs through use of airborne in situ observations of ice crystals and water droplets from a recent Spring campaign in the Norwegian Sea (ISLAS2022). As individual flights only offer snapshots into certain parts of the mCAO evolution, a composite approach has been developed that integrates the in situ microphysical observations from multiple flights in order to capture the entire mCAO development. Thin, low ice clouds were observed over sea ice, reaching cloud top altitudes around 1200 m high. A rapidly developing "stratiform" region has been observed, where liquid-topped mixed-phase clouds increase in vertical extent, as the boundary layer deepens with increasing distance from the sea ice edge. At around 600 km fetch, rapid glaciation in a subsequent "convective" region leads to deep (up to 4500 m cloud top), almost completely glaciated, precipitating clouds that are reaching the end of their lifetime. While the observed microphysical properties are in agreement with earlier studies, the study highlights the potential of the composite approach in moving away from individual case studies to a more holistic microphysical picture of mCAOs, especially when statistics are improved by including additional campaign datasets in the future.
This paper introduces a new methodological framework for studying marine Cold Air Outbreaks (mCAOs). By integrating in situ airborne data collected from multiple flights during the ISLAS2022 campaign, the authors go beyond isolated "snapshot" case studies, offering a comprehensive perspective on cloud development from sea ice to open ocean. The manuscript is well-prepared and suitable for publication, although I have a few minor suggestions for improvement.
135-140: The authors assume that all particles with a measurement below 0 degrees Celsius are classified as ice by the CIP. It would be beneficial to address the presence of large supercooled droplets, which are often found in mCAOs, as the CIP is unable to distinguish between these large supercooled droplets and ice crystals. This potential misclassification of supercooled droplets could lead to significant errors in SLF values later on.
430-440: Does this field campaign include INPs or CCN observations? It would be beneficial to incorporate INPs and CCN measurements analysis to support your interpretations.
440: This hypothesis would benefit from a more detailed examination of LWF vs Temperature, rather than the isolated contours currently depicted in Figure 5.
Some mechanisms, physical-process interpretations, and literature comparisons may be better suited to the Discussion section. For example, lines 265-270: This indicates that the crystals ...
The discussion section could benefit from a more schematic conceptual model, with the physical mechanisms (arrows and process names) labeled directly on the diagram, rather than repeating them in both the results and discussion sections.