The Global Precipitation Measurement Mission: Product Validation and Model Evaluation Studies

The Global Precipitation Measurement (GPM) mission, an international satellite constellation of microwave remote sensors that observes global precipitation, aims to improve our understanding of the Earth’s water cycle and energy budget. This thesis validates GPM’s constellation-reference sensors over the British Isles, studies the global diurnal cycle of precipitation using GPM, and evaluates climate model performance in simulating the global diurnal cycle. These studies are of paramount importance to science and society, by providing necessary understanding of GPM’s mid-latitude performance prior to its application to the global diurnal cycle of precipitation, which climate models notoriously fail to accurately represent. Identifying climate model shortcomings with accurate observations is critical to improving their realism in simulating the future climate. This thesis first validates the constellation reference NASA-JAXA GPM Core Observatory (CO) Dual-frequency Precipitation Radar (DPR) and GPM Microwave Imager (GMI) precipitation retrievals over the British Isles against the Met Office ground-based radar network. The DPR and combined DPR-GMI retrievals underestimate British-Irish precipitation by 31% and 21%, respectively, with a tendency for winter bias enhancements due to erroneous surface precipitation retrievals in the presence of low freezing levels. The second study investigates the global precipitation diurnal cycle using the global-gridded Integrated Multi-satellitE Retrievals for GPM (IMERG) product, derived from the GPM passive microwave constellation, spaceborne infrared and ground-based gauge sensors. The diurnal cycle is identified to be stronger over land, where precipitation peaks at ~16–24 local solar time (LST), than over ocean, where precipitation peaks at ~0–8 LST (~8–15 LST) over open (coastal) waters. The final study evaluates the global diurnal precipitation representation of three Coupled Model Intercomparison Project (CMIP6) models and the ECMWF Reanalysis (ERA5) using IMERG. Three CMIP6 models and ERA5 are found to simulate precipitation earlier than observed, with difficulty in capturing the nocturnal propagation of precipitation over mountainous regions.