Cloud Particle Habits over the Southern Ocean during the HALO-South Aircraft Campaign

The interactions and effects of aerosols and clouds are significant uncertainties in assessing and modeling climate change. Remote regions on earth with frequent pristine aerosol conditions, where the effect of aerosols on clouds are largest, are becoming increasingly rare due to human influence. Understanding climate and global environmental changes makes these locations of particular scientific interest. The Southern Ocean (SO), is one of the cloudiest regions on earth with a high cloud radiative effect and a high bias in atmospheric models due to an underestimation of aerosols. To address this, the HALO-South aircraft campaign, conducted in September and October 2025, aimed to investigate the interplay between aerosols, clouds, and radiation in this region. Within this framework, cloud particle habit – encompassing particle shape, complexity, phase, size and number concentration – is a key microphysical property linking atmospheric thermodynamics to cloud optical properties and precipitation processes.

The optical sensor PHIPS-HALO was employed to produce images of individual cloud particles allowing to analyse microphysical characteristics in great detail. We present an overview of cloud particle habits observed in the SO during the HALO-South campaign, providing insight into the evolution of cloud types and relating observed particle characteristics to established temperature and saturation regimes.

 

Acknowledgments: This work was supported by the DFG (Deutsche Forschungsgemeinschaft, German Research Foundation), Priority Program SPP 1294, the Max Planck Society, the German Aerospace Center (DLR) and the Leibniz Institute for Tropospheric Research (TROPOS).