Morphological Regimes and their Spatial Scales in Low-Level Mixed-Phase Stratocumuli in the Southern Ocean

Marine stratocumuli are divided into different self-organized morphological regimes. The organized cellular regimes are referred to as open and closed mesoscale-cellular convective (MCC) clouds and are frequently observed in the Southern Ocean. There, many MCC clouds are mixed-phase clouds containing a mixture of ice and liquid. These MCC clouds exert substantial radiative cooling especially in the Southern Ocean. The cloud albedo of closed MCC cells is on average higher than of open MCC cells even for the identical cloud fraction (McCoy et al. 2017). We investigate whether cloud phase influences the spatial scale of MCC cells and how differences are associated with cloud-radiative effects.

We examine the cloud phase with a vertically integrated cloud phase based on raDAR-liDAR (DARDAR) data product from the Cloud-Aerosol-Water-Radiation Interactions (ICARE) Data and Services Center (Danker et al. 2022). Currently, we are building and testing an algorithm identifying cellular organization and distribution of cell size in shortwave radiance retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua. We have tried different image segmentation techniques. The most promising results are obtained by applying the random walker image segmentation to selected scenes along the DARDAR track combined with a neural network classification of MCC clouds from Wood and Hartmann (2006).

We will present the skill and limitation of this approach in obtaining cell-size statistics within open and closed MCC clouds. Further, we will show scientific results regarding the relationship between cloud phase and cell-size in open and closed MCC clouds in the Southern Ocean as well as changes in cloud albedo with cell-size.