The Diurnal Cycle of Precipitation: A Comparison of State-of-the-Art Observations and Models

Representation of the diurnal cycle is a key trial of the ability of models to capture precipitation timing, duration, and intra-daily variations.  The state-of-the-art model simulations from the Coupled Model Intercomparison Project (CMIP6), which are set to inform the upcoming IPCC sixth assessment report, are yet to be compared to the diurnal cycle of precipitation according to observations.  The recently released version 6 of the Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG) product provides over 19 years of global-gridded observations (June 2000 - Present).  Such state-of-the-art observations, with inputs from space-borne dual-frequency radar, microwave radiometers, infrared sensors and ground-based gauges, have never been available at 0.1˚ gridding every half hour over such a long period.  This study aims to compare the amplitude and time of maximum precipitation accumulation between IMERG observations and CMIP6 models over an 8-year period (June 2000 – May 2008).  Preliminary results suggest that the CMIP6 models typically underestimate the amplitude of precipitation accumulation over land compared to observations, though there are overestimates in the Amazon and across central Africa.  Furthermore, the CMIP6 models typically lag behind observations in their time of maximum accumulation over land; observations suggest a late evening to night maximum whilst CMIP6 models show a late morning to early afternoon maximum.  The results will be beneficial to improving modelling of precipitation across the globe.