Using Himiwari-9 cloud tracking to support the analysis of measurements from the ACADIA and HALO-South field campaigns

The large horizontal grid size of current atmospheric models means that subgrid  heterogeneity in cloud properties must be parameterised. A number of studies have suggested that this heterogeneity may have significant negative consequences for the representation of mixed phase clouds, marine boundary layer clouds and stratocumulus cloud decks in models. This study details work which uses high temporal (10 minute) and spatial resolution (4 km) Advanced Himawari Imager data collected by the Himawari-9 geostationary satellite to identify and track coherent cloud objects. In particular, we track cloud data in the South West Pacific centred on New Zealand during the HALO-South and ACADIA field campaigns. HALO-South is an airborne campaign using the HALO research aircraft deployed from New Zealand in September to October 2025 to study Southern Ocean clouds and aerosol-cloud interactions, while the ACADIA campaign is a longer term deployment of ground-based remote sensing instrumentation to sample the cloud and aerosol environment at two sites in New Zealand.

This work details the derivation of coherent cloud objects by identifying features using cloud top temperatures and the application of a watershedding segmentation scheme to identify coherent regions. These coherent cloud objects are then tracked between individual images using the “tobac” tracking scheme.  The tracked Himiwari-9 cloud information is then used to examine the heterogeneity of cloud properties, particularly cloud phase, inside and across these coherent cloud objects in the South West Pacific. With a normalised version of the largest length of conistent cloud properties within a coherent cloud object being used as our measure of spatial heterogenity. Results of cloud tracking are also used in an effort to analyse heterogeneity as a function of cloud lifetime by associating cloud properties with individual coherent cloud objects across their evolution. Coherent cloud objects identified from Himawari-9 satellite imagery are then compared with remotely sensed cloud data at the ACADIA field sites to examine the spatial and temporal consistency between ground-based and satellite-based remote sensing perspectives. We also examine the potential to identify coherent cloud regions along flight transects completed during the HALO-South campaign.