A baseline cloud climatology for Aotearoa New Zealand and the Southwest Pacific region 

This study presents a cloud climatology over Aotearoa New Zealand and the surrounding Southwest Pacific Ocean region (140-210°E, 10-70°S) using satellite observations, ground measurements and reanalysis data. Three cloud satellite datasets alongside a network of ceilometers operated by the New Zealand Metservice are used to observe cloud properties.  Sixteen ceilometer sites, nine sites in the North Island, six sites in the South Island and one on Chatham Island, makes up the ground measurement network with data from 2021 to 2023. Cloud occurrence data at each site are compared with the ERA5, MERRA-2 and JRA55 reanalyses using a ground-based instrument simulator. Initial results show that both cloud occurrence is better represented in the models at east coast sites, with ERA5 performing the best of the three reanalyses. Satellite datasets include MODIS Aqua/Terra cloud properties (2003–2025), Himawari-9 Advanced Himawari Imager cloud products (2023–2025), and observations from Cloudsat/CALIOP (2007–2010). We compare cloud fraction data from these satellite datasets with ERA5 reanalyses processed using the COSP instrument simulator to aid comparability. We then compare cloud top pressure/cloud top height/cloud top temperature distributions from the MODIS and Himawari-9 datasets with vertical profiles of cloud occurrence statistics from the CloudSat/CALIOP 2BCL5 dataset and from ERA5.  Cloud regimes are identified using MODIS cloud-top pressure–optical depth histograms, and their occurrence statistics are compared with CloudSat/CALIOP 2B-CLDCL5 cloud-type classifications.  Synoptic drivers for cloud fraction and other cloud properties are also examined via comparison with the Kidson weather types, a set of 12 objectively classified daily weather patterns centred over New Zealand, derived from cluster analysis of 1000 hPa geopotential height fields to form a synoptic climatology.